- Email: [email protected]
Hyperactivity Disorder: A Nationwide Cohort Study
Accepted Manuscript Teenage Parenthood and Birth Rates for Individuals With and Without AttentionDeficit/Hyperactivity Disorder: A Nationwide Cohort Study Søren D. Østergaard, MD, PhD, Søren Dalsgaard, MD, PhD, Stephen V. Faraone, PhD, Trine Munk-Olsen, PhD, Thomas M. Laursen, PhD PII:
S0890-8567(17)30205-8
DOI:
10.1016/j.jaac.2017.05.003
Reference:
JAAC 1753
To appear in:
Journal of the American Academy of Child & Adolescent Psychiatry
Received Date: 23 January 2017 Revised Date:
5 April 2017
Accepted Date: 4 May 2017
Please cite this article as: Østergaard SD, Dalsgaard S, Faraone SV, Munk-Olsen T, Laursen TM, Teenage Parenthood and Birth Rates for Individuals With and Without Attention-Deficit/Hyperactivity Disorder: A Nationwide Cohort Study, Journal of the American Academy of Child & Adolescent Psychiatry (2017), doi: 10.1016/j.jaac.2017.05.003. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT Teenage Parenthood and Birth Rates for Individuals With and Without Attention-Deficit/Hyperactivity Disorder: A Nationwide Cohort Study RH = Teenage Parenthood in ADHD Søren D. Østergaard, MD, PhD, Søren Dalsgaard, MD, PhD, Stephen V. Faraone, PhD, Trine Munk-Olsen, PhD, Thomas M. Laursen, PhD
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Supplemental material cited in this article is available online. Accepted May 5, 2017
This article was reviewed under and accepted by Ad Hoc Editor James F. Leckman, MD.
Dr. Østergaard is with Aarhus University Hospital, Aarhus, Denmark; The Psychosis Research Unit, Aarhus University Hospital, Risskov, Denmark; and The Lundbeck Foundation Initiative for Integrative Psychiatric
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Research (iPSYCH), Aarhus. Dr. Dalsgaard is with The National Centre for Register-Based Research, Aarhus University, iPSYCH, and Hospital of Telemark, Kragerø, Norway. Dr. Faraone is with State
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University of New York (SUNY) Upstate Medical University, Syracuse, and The K.G. Jebsen Centre for Neuropsychiatric Disorders, University of Bergen, Bergen, Norway. Dr. Munk-Olsen is with The National Centre for Register-Based Research, and iPSYCH. Dr. Laursen is with The National Centre for RegisterBased Research, iPSYCH, and The Centre for Integrated Register-based Research at Aarhus University (CIRRAU), Aarhus.
The study is supported by a grant from the Lundbeck Foundation. The funding body had no influence on the
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study design; the collection, analysis and interpretation of data; writing of the report; and the decision to submit the article for publication.
Dr. Østergaard is supported by a grant from the Lundbeck Foundation. Dr. Faraone is supported by the K.G. Jebsen Centre for Research on Neuropsychiatric Disorders, University of Bergen, Bergen, Norway, the European Union's Seventh Framework Programme for research, technological development and
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demonstration under grant agreement no 602805, the European Union's Horizon 2020 research and innovation programme under grant agreement No 667302, and NIMH grant 5R01MH101519.
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Dr. Laursen served as the statistical expert for this research. Disclosure: In the past 2 years, Dr. Faraone has received income, potential income, travel expenses, continuing education support, and/or research support from Lundbeck, Rhodes, Arbor, KenPharm, Ironshore, Shire, Akili Interactive Labs, CogCubed, Alcobra, VAYA, Sunovion, Genomind and Neurolifesciences. With his institution, he has US patent US20130217707 A1 for the use of sodium-hydrogen exchange inhibitors in the treatment of ADHD. In previous years, he has received support from Shire, Neurovance, Alcobra, Otsuka, McNeil, Janssen, Novartis, Pfizer, and Eli Lilly and Co. He has received royalties from books published by Guilford Press (Straight Talk about Your Child’s Mental Health), Oxford University Press (Schizophrenia: The Facts), and Elsevier (ADHD: Non-Pharmacologic Interventions). He is principal investigator of www.adhdinadults.com. Drs. Østergaard, Dalsgaard, Munk-Olsen, and Laursen report no biomedical financial interests or potential conflicts of interest.
ACCEPTED MANUSCRIPT Correspondence to Søren Dinesen Østergaard, MD, PhD, Psychosis Research Unit, Aarhus University,
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Hospital, Risskov, Skovagervej 2, 8240 Risskov; email: [email protected]
ACCEPTED MANUSCRIPT ABSTRACT Objective: Prior studies have established that attention-deficit/hyperactivity disorder (ADHD) is associated with risky sexual behavior, but it remains unknown whether individuals with ADHD are also more likely to become parents while being teenagers. This aspect is clinically relevant since
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teenage parenthood is associated with adverse outcomes for both parents and children. Therefore, the main aim of this study was to investigate whether individuals with ADHD are more likely to become teenage parents compared to individuals without ADHD.
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Method: This is a historical prospective cohort study based on nationwide data from Danish registers. The cohort consisted of all individuals (N=2,698,052) born in Denmark from January 1st
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1960 to December 31st 2001. The association between ADHD (n=27,479 cases) and parenthood (first child) in age intervals 12-16, 17-19, 20-24, 25-29, 30-34, 35-39, and 40+ years was investigated by means of Poisson regression and expressed as incidence rate ratios (IRRs) with accompanying 95% CIs. The IRRs can be interpreted as relative risks.
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Results: Compared to individuals without ADHD, those with ADHD were significantly more likely to become parents at age 12-15 (IRR for females: 3.62 [95%CI 2.14-6.13] and for males: 2.30
[95%CI 1.90-2.70]).
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[95%CI 1.27-4.17]) and at age 16-19 (IRR for females: 1.94 [95%CI 1.62-2.33] and for males: 2.27
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Conclusion: Individuals with ADHD are significantly more likely to become teenage parents compared to individuals without ADHD. Therefore, it may be appropriate to target this group with an intervention program including sexual education and contraceptive counseling. Key words: Attention-deficit/hyperactivity disorder; Parenthood; Birth rate
INTRODUCTION Attention-deficit/hyperactivity disorder (ADHD) is a neurodevelopmental disorder that affects approximately 5% of children and adolescents.1 The inattentive and hyperactive-impulsive
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ACCEPTED MANUSCRIPT symptoms of ADHD place a significant burden on those affected in terms of difficulties in interpersonal relationships,2 poor educational attainment,3 decreased lifetime earnings,4 criminal behavior,5,6 accidents,7 comorbid substance use disorders,8 and increased risk of premature mortality.9
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Another feature of ADHD, which is likely to have adverse consequences, is risky sexual behavior. This aspect has received some attention from researchers in recent years. For instance, in a sample of 115 adolescents (aged 12-17, 84% males) involved in the US Juvenile Drug Court,
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Sarver and colleagues showed that ADHD was associated with risky sexual behavior among those with comorbid oppositional defiant disorder (ODD) or conduct disorder (CD). This association was
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primarily mediated by problematic alcohol/marijuana use.10 Similarly, in a cohort of young adults (aged 19-25, 91% males) followed for at least 13 years, Barkley et al. reported that hyperactive individuals (n=149) were significantly younger at first sexual intercourse, had more sex partners, and were significantly more likely to have been involved in a pregnancy, compared to a community
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control group (n=72).11 In a study of college students, Huggins et al. showed that females with ADHD (n=24, mean age= 20 years, SD=1) were more likely to have sex without using a condom compared to females without ADHD (n=28, mean age 19 years, SD=1), males without ADHD
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(n=20, mean age=19 years, SD=1) and males with ADHD (n=20, mean age=20 years, SD=2).12 To
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our knowledge, Huggins et al. is the only study reporting data regarding risky sexual behavior specifically in females with ADHD. Finally, in a sample of 175 young men with ADHD and 111 controls (aged 18-26), Flory and colleagues reported that childhood ADHD predicted earlier initiation of sexual activity, more casual sex, more sexual partners, and more pregnancies.13 Risky sexual behavior may be associated with a series of adverse outcomes, such as sexually transmitted diseases, non-spontaneous abortions, and teenage parenthood. In this study, we focused on the latter, namely whether individuals with ADHD are more likely to become parents while being teenagers. This has not been investigated previously and is of significant interest due to the
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ACCEPTED MANUSCRIPT substantial literature documenting that teenage parenthood is associated with a significantly increased risk of adverse outcomes for both the young parents (low educational attainment, single habitation, welfare dependency, and disability pension)14,15 and their children (preterm birth, low birth weight, low Apgar scores, increased neonatal mortality, low educational achievement, low
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income and low life satisfaction).16-19 Furthermore, we investigated whether individuals with
following research questions were addressed: When compared to individuals without ADHD:
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ADHD have more children compared to individuals without ADHD over time.20 Specifically, the
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I) … are individuals with ADHD more likely to become parents while being teenagers? II) … are individuals with ADHD more likely to become parents in general? III) … are individuals with ADHD who have children more likely to have many children? IV) … do individuals with ADHD on average have more or fewer children? METHOD
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Cohort
This is a population-based historical prospective cohort study. The dataset used in the study was obtained by register linkage via the unique personal registration numbers, which are assigned to
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all Danes at the time of birth and registered in the Danish Civil Registration System.21 The cohort
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was defined as all individuals born in Denmark from January 1st 1960 to December 31st 2001 who were alive and residing in Denmark on January 1st 1980 and/or at their 12th birthday, whichever came last. Based on the observation that some individuals in the cohort had already become parents by the age of 12, we decided to include the 12-year-olds in our definition of teenagers (i.e., age 1219). Definition of Parenthood Consistent with a prior Danish study of the reproductive pattern in individuals with mental disorders,22 parenthood was defined via link to a child born in Denmark in the Danish Civil
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ACCEPTED MANUSCRIPT Registration System.21 Definition of ADHD Individuals having received an International Classification of Diseases–8th Revision (ICD8)23 diagnosis of 308.01 or an International Classification of Diseases–10th Revision (ICD-10)24
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diagnosis of F90.x or F98.8 following either inpatient or outpatient treatment at psychiatric, pediatric or neurological departments in Denmark9 were defined as ADHD cases from the date the diagnosis was assigned. Diagnostic data regarding ADHD for the cohort members was extracted
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from the Danish Psychiatric Central Research Register (DPCRR)25,26 and from the Danish National Patient Register (DNPR).27 In these two registers, the ICD-8 was used as diagnostic reference until
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January 1st 1994, when it was replaced by the ICD-10. Until December 31st 1994, only diagnoses assigned following inpatient treatment were registered in the DPCRR. From January 1st 1995 and onwards, diagnoses assigned following outpatient treatment were included as well. Statistics and Follow-Up for Each Research Question
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The data was analyzed by means of Poisson regression (survival analysis) using the logarithm of the number of person-years at risk as an offset variable. This method approximates a Cox regression28 and takes the length of follow-up for each cohort member into account. Incidence
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rates were compared between those having developed ADHD with those not having developed
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ADHD, by calculating incidence rate ratios (IRRs), which can be interpreted as relative risks. All IRRs were stratified by sex and adjusted for calendar year (1 year strata [time dependent]), and the age of the cohort members (1 year strata [time dependent]). The 95% CIs for the IRRs and the p-values were based on likelihood ratio tests with .05 as the threshold for statistical significance. All analyses were carried out using SAS version 9.4 (SAS Institute Inc, Cary, NC). The exact definition of the cohort and the follow-up period varied depending on the nature of the research question. Below, these variations are specified for each of the four research questions:
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ACCEPTED MANUSCRIPT I) … are individuals with ADHD more likely to become parents while being teenagers? To answer this question the cohort members were followed from January 1st 1980 or from their 12th birthday, whichever came last. The follow-up ended at childbirth, emigration, death, loss to followup, or January 1, 2013, whichever came first. Specifically, we calculated IRRs for having a child
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within the following age intervals among females: 12-16, 17-19, 20-24, 25-29, 30-34, 35+ and for the following intervals among males: 12-16, 17-19, 20-24, 25-29, 30-34, 35-39, 40+.
II) … are individuals with ADHD more likely to become parents in general? For this research
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question the cohort members were followed from January 1, 1980 or from their 12th birthday,
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whichever came last. The follow-up ended at childbirth, emigration, death, loss to follow-up, or January 1, 2013, whichever came first. Since we followed the eldest cohort members up to the age of 53 years, the IRRs calculated in this analysis roughly reflect the likelihood of females and males diagnosed with ADHD becoming parents, compared to those without ADHD. III) … are individuals with ADHD who have children more likely to have many children? Here
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we calculated the IRRs for progression from having child number one to child number two, from child number two to child number three, from child number three to child number four, and from child number four to child number five. In these analyses, we followed up individuals from the birth
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of their first, second, third, and fourth child, respectively. The follow-up ended at the subsequent
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childbirth, emigration, death, loss to follow-up, or January 1, 2013, whichever came first. IV) … do individuals with ADHD on average have more or fewer children? To answer this question, we calculated the average number of children that females and males with and without ADHD respectively had had by the ages of 20, 25, 30, and 40 years. Finally, to assess whether the answers to the analytical research questions I-III (research question IV is of descriptive nature) were driven by confounding rather than by ADHD, we repeated the analyses described above, while adding adjustment for the following covariates: paternal (father of the cohort members) history of mental disorders (with the following levels:
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ACCEPTED MANUSCRIPT unknown father, no contact with psychiatric services, any diagnosis assigned by psychiatric services (ICD-8 diagnoses 290-315, and ICD-10 diagnoses F00-F99) apart from bipolar disorder or schizophrenia (ICD-8 diagnoses 295.x9 [excluding 295.79], 296.19, 296.39, 298.19, and ICD-10 diagnoses F20, F30, F31, bipolar disorder or schizophrenia),25 maternal (mother of the cohort
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members) history of mental disorders (identical levels as for the father), paternal education level (with the following levels: unknown father, unknown education level, compulsory schooling, highschool/technical education/short-cycle higher education, medium-cycle higher education, long-
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cycle higher education),29 maternal education level (identical levels as the father), paternal
occupation status (with the following levels: unknown father, unknown occupation status, under-
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educated, employed, unemployed, outside the workforce),30 maternal occupation (identical levels as the father), ODD or CD of the cohort members (ICD-8 diagnoses 308.03 and 308.04, and ICD-10 diagnoses F91.x and F90.1), substance use disorder (SUD) of the cohort members (ICD-8 diagnoses 291.x9, 294.39, 303.x9, 303.20, 303.28, 303.90, 304.x9, and ICD-10 diagnoses F10–F19), bipolar
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disorder of the cohort members (ICD-8 diagnoses 296.19, 296.39, 298.19, and ICD-10 diagnoses F30-F31), and schizophrenia of the cohort members (ICD-8 diagnoses 295.x9 [excluding 295.79], and ICD-10 diagnosis F20). Parental mental disorder and comorbid ODD/CD, SUD, bipolar
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disorder, or schizophrenia were treated as time-dependent covariates, while parental education level
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and occupation status were assessed at age 15 of the cohort members (or the year closest to age 15 with available data). We did not include the education level and occupation status of the cohort members in the adjusted analyses as deviations from the general population on these parameters are likely to be on the causal path from ADHD to a specific reproductive pattern rather than representing confounders of this association. RESULTS The established cohort comprised 2,698,052 individuals (1,384,334 males and 1,313,718 females) of which 27,479 (20,093 males and 7,386 females) had received an ADHD diagnosis
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ACCEPTED MANUSCRIPT during follow-up. The results pertaining to the three analytical research questions (I-III) and the descriptive research question (IV) are as follows: I) … are individuals with ADHD more likely to become parents while being teenagers? The IRRs for becoming a parent within various age intervals are shown in Figure 1 (stratified by sex).
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Individuals with ADHD were significantly more likely to become parents at ages 12-15 (IRR for females: 3.62 [95%CI 2.14-6.13] and for males: 2.30 [95%CI 1.27-4.17]) and at ages 16-19 (IRR for females: 1.94 [95%CI 1.62-2.33] and for males: 2.27 [95%CI 1.90-2.70]). Conversely,
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individuals with ADHD were significantly less likely to become parents at 25 years and older.
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Figure 1 approximately here
II) … are individuals with ADHD more likely to become parents in general? The IRRs for becoming a parent were 0.56 (95%CI 0.53-0.60) for males with ADHD and 0.70 (95%CI 0.64-0.76) for females, compared to the reference value (1.00) for males and females without ADHD. Thus,
females without ADHD.
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both males and females with ADHD were significantly less likely to become parents than males and
III) … are individuals with ADHD who have children more likely to have many children? The IRRs for individuals with ADHD progressing from having child number one to child number two,
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from child number two to child number three, from child number three to child number four, and
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from child number four to child number five are shown in Table 1. Compared to males without ADHD, males with ADHD were significantly less likely to progress from having child number one to child number two, but significantly more likely to progress from having child number three to number four. The pattern was similar for females with ADHD who were significantly less likely to progress from having child number one to child number two, but significantly more likely to progress from having child number four to number five. Table 1 approximately here IV) … do individuals with ADHD on average have more or fewer children? The average number
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ACCEPTED MANUSCRIPT of children that females and males with and without ADHD, respectively, had had at the ages of 20, 25, 30, 35, and 40 years is shown in Table 2. These results show that males with ADHD had had significantly more children than those without ADHD by the ages of 20 and 25, but significantly fewer by the ages of 30, 35, and 40 years. For females, those with ADHD had on average
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significantly more children than those without ADHD by the ages of 20 and 25 years, while the number of children by the ages of 30, 35, and 40 was roughly the same for the two groups. Table 2 approximately here
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The significant differences reported for the analytical research questions I-III withstood
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adjustment for paternal history of mental disorders, maternal history of mental disorders, paternal education level, maternal education level, paternal occupation status, maternal occupation status, and comorbid ODD/CD, SUD, bipolar disorder, or schizophrenia of the cohort members (results reported in Table S1 and Figure S1, available online), with one exception: females with ADHD
adjusted analysis. DISCUSSION
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were not significantly more likely to progress from having child number four to number five in the
The results of this nationwide cohort study of 2,698,052 individuals show that individuals
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with ADHD (n=27,479) differed from those without ADHD (n=2,670,573) on all of the
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investigated aspects regarding the age of parenthood and birth rates. Compared to individuals without ADHD, those with ADHD I) are more likely to become parents while being teenagers, II) are less likely to become parents in general, III) are more likely to have many children (three or more for males and four or more for females) if they do become parents, and IV) have fewer children on average (only males). The adjusted analyses indicated that this pattern is likely to be a consequence of ADHD and not of confounding, except from the increased likelihood of females having many children if they do become parents, which was not significant after adjustment. To our knowledge, this study is the first to study the association between ADHD and the age at parenthood
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ACCEPTED MANUSCRIPT /number of births in a very large population-based cohort with follow-up covering virtually the entire reproductive life. Therefore, the results presented here are largely unprecedented and provide new knowledge on the consequences of ADHD. From a clinical perspective, the most important finding of this study is that individuals with
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ADHD are significantly more likely to become parents during their teenage years compared to individuals without ADHD (Figure 1). This is consistent with the finding by Barkley et al., who showed that being diagnosed with hyperactivity was associated with relatively early parenthood
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(mean age at follow-up = 20 years).11 This finding is of interest due to the substantial literature
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documenting that teenage parenthood is associated with a significantly increased risk of adverse outcomes for both the young parents (low educational attainment, single habitation, welfare dependency, and disability pension)14, 15 and their children (preterm birth, low birth weight, low Apgar scores, increased neonatal mortality, low educational achievement, low income, and low life satisfaction).16-19 These associations have been considered to be sufficiently strong and the outcome
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sufficiently adverse to merit preventive interventions to reduce teenage pregnancies.31-34 Our finding that individuals with ADHD are more likely to become parents during their teenage years indicates that it may be appropriate to target this group with a multifactorial program including
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sexual education and contraceptive counseling. Indeed, such initiatives may be of particular
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importance among those with ADHD, since parenting in general is known to be difficult for these individuals.35, 36 Being a teenage parent with ADHD is likely to be even more challenging. It would seem that such sexual education and contraceptive counseling should ideally be organized by the mental health professionals who are responsible for the diagnosis and treatment of ADHD, as they are likely to be able to address the issue in a timely manner. Otherwise, there is a substantial risk of intervening too late, only being able to address the risk of repeat teenage pregnancies.33 We are not aware of any evidence-based intervention programs addressing this challenge in relation to ADHD, but when designing such an initiative, experience from the successful young parent program to
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ACCEPTED MANUSCRIPT reduce repeat teen pregnancy, described by Omar et al,33 could be used as a source of inspiration. The other findings of our study regarding the reproductive rates of individuals with ADHD can be summarized as follows: many have no children, yet few have many children. Indeed, the overall likelihood for individuals with ADHD to become parents was significantly lower than that
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of individuals without ADHD. This is consistent with our prior findings from schizophrenia, bipolar disorder, and major depression,22 indicating that mental disorders in general are associated with a decreased likelihood of becoming a parent. However, when taking a closer look at the individuals
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with ADHD who did become parents, we observed that they were more likely to have more
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children than those without ADHD. As a consequence, the mean number of children born to females with ADHD was similar to that of females without ADHD (at the age of 30, 35, and 40). The males with ADHD did not, however, “catch up” in this manner as their mean number of offspring was significantly lower than for males without ADHD (at the age of 30, 35, and 40). While this finding may be partly explained by differential registration of paternities (more
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unregistered paternities among males with ADHD compared to males without ADHD – perhaps particularly pronounced for young fathers), the difference is so substantial that it is unlikely to be fully accounted for by unregistered paternities. Therefore, this result supports prior findings
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suggesting that, from a reproductive perspective, mental disorders have more severe consequences
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for males than for females.22,37 The reasons underlying this sex difference cannot be determined based on the data at hand, but it is likely to reflect that females have the ultimate say in whether a pregnancy should be carried to term or not. In other words, if a female with ADHD wants a child, she can, in most cases, make that decision when becoming pregnant. For a male with ADHD who wants to have a child, he will need a female partner who will have his child. The most significant limitation of this study is our use of a register-based definition of ADHD. The diagnoses in the registers providing data for this study are assigned as part of normal clinical practice and not necessarily based on standardized research interviews. However, the validity of the
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ACCEPTED MANUSCRIPT ADHD diagnoses has been found to be acceptable.38,39 The ICD-8 definition of ADHD is probably less reliable than the ICD-10 definition.38,39 Therefore, we conducted a sensitivity analysis in which we addressed the main research question (are individuals with ADHD more likely to become teenage parents compared to individuals without ADHD) in a restricted cohort consisting of
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individuals born from January 1, 1980 to December 31, 2001 and followed up regarding parenthood from January 1, 1994 to January 1, 2013. Within this cohort we only considered ICD-10 diagnoses of ADHD (diagnosed from January 1, 1994). The results of this strictly ICD-10-based analysis (see
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Table S2, available online) confirmed those of the ICD-8 + ICD-10-based analysis, as it showed
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that both males and females with ADHD were more likely to become teenage parents than their peers without ADHD. In addition to being an indirect confirmation of the validity of the ICD-8 definition of ADHD, this result also indicates that the association between ADHD and early parenthood has been relatively stable over the observation period covered by this study (January 1, 1980 to January 1, 2013).
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The register-based definition of ADHD also has implications for the external validity of our findings. This is due to the fact that psychiatrists and pediatricians in private practice, who diagnose and treat a minority of ADHD cases in Denmark, do not report diagnoses to the registers. Therefore,
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our results may not generalize to patients seen in these private practices. That being said, it is our
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impression that the differences in reproductive patterns between individuals with and without ADHD described in this article are likely to be generalizable to other settings and cultures as they seem to fit well with the core psychopathology of ADHD, which is relatively independent of these aspects.40
Another potential limitation is that parenthood is defined via the Civil Registration System (legal parenthood), which corresponds to biological parenthood in the vast majority of cases, but there may be some misclassifications – i.e., children, who have been adopted by stepparents etc. However, this is only of minor concern, as such adoptions are rare in Denmark.41
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ACCEPTED MANUSCRIPT In conclusion, the results of this nationwide cohort study show that, compared to individuals without ADHD, those with ADHD I) are more likely to become parents while being teenagers, II) are less likely to become parents in general, III) are more likely to have many children if they do become parents, and IV) have less children on average (only males). From a clinical perspective,
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the most important finding of our study is that individuals with ADHD are significantly more likely to become parents during their teenage years compared to individuals without ADHD. Since teenage parenthood is associated with a number of adverse outcomes for both parents and children,
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it may be of relevance to target this group with an intervention program (including sexual education
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and contraceptive counseling) to reduce the number of teenage pregnancies. REFERENCES
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ACCEPTED MANUSCRIPT 18. Chen XK, Wen SW, Fleming N, Demissie K, Rhoads GG, Walker M. Teenage pregnancy and adverse birth outcomes: A large population based retrospective cohort study. Int J Epidemiol. 2007;36:368-373. 19. Igwegbe AO, Udigwe GO. Teenage pregnancy: Still an obstetric risk. J Obstet Gynaecol.
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23. Danish National Board of Health. Classification of diseases: Extended danish-latin version of the world health organization international statistical classification of diseases and related health
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problems, 8th revision. Copenhagen, Denmark: Danish National Board of Health; 1971. 24. World Health Organization. The ICD-10 classification of mental and behavioural disorders. diagnostic criteria for research. Geneva: WHO; 1993.
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25. Mors O, Perto GP, Mortensen PB. The danish psychiatric central research register. Scand J
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Public Health. 2011;39:54-57.
26. Munk-Jorgensen P, Ostergaard SD. Register-based studies of mental disorders. Scand J Public Health. 2011;39:170-174.
27. Lynge E, Sandegaard JL, Rebolj M. The danish national patient register. Scand J Public Health. 2011;39:30-33. 28. Andersen PK, Borgen Ø, Gill RD, Keiding N. Statistical models based on counting processes. New York: Springer-Verlag; 1993. 29. Jensen VM, Rasmussen AW. Danish education registers. Scand J Public Health. 2011;39:91-4.
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ACCEPTED MANUSCRIPT 30. Petersson F, Baadsgaard M, Thygesen LC. Danish registers on personal labour market affiliation. Scand J Public Health. 2011;39:95-98. 31. Pfitzner MA, Hoff C, McElligott K. Predictors of repeat pregnancy in a program for pregnant teens. J Pediatr Adolesc Gynecol. 2003;16:77-81.
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32. Lavin C, Cox JE. Teen pregnancy prevention: Current perspectives. Curr Opin Pediatr. 2012;24:462-469.
33. Omar HA, Fowler A, McClanahan KK. Significant reduction of repeat teen pregnancy in a
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comprehensive young parent program. J Pediatr Adolesc Gynecol. 2008;21:283-287.
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34. Wellings K, Palmer MJ, Geary RS, et al. Changes in conceptions in women younger than 18 years and the circumstances of young mothers in england in 2000-12: An observational study. Lancet. 2016;388:586-595.
35. Murray C, Johnston C. Parenting in mothers with and without attention-deficit/hyperactivity disorder. J Abnorm Psychol. 2006;115:52-61.
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36. Williamson D, Johnston C, Noyes A, Stewart K, Weiss MD. Attention-deficit/hyperactivity disorder symptoms in mothers and fathers: Family level interactions in relation to parenting. J Abnorm Child Psychol. 2017;45:485-500.
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37. McGrath JJ, Hearle J, Jenner L, Plant K, Drummond A, Barkla JM. The fertility and fecundity
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of patients with psychoses. Acta Psychiatr Scand. 1999;99:441-446. 38. Linnet KM, Wisborg K, Secher NJ, et al. Coffee consumption during pregnancy and the risk of hyperkinetic disorder and ADHD: A prospective cohort study. Acta Paediatr. 2009;98:173-179. 39. Dalsgaard S, Hansen N, Mortensen PB, Damm D, Thomsen PH. Reassessment of ADHD in a historical cohort of children treated with stimulants in the period 1969-1989. Eur Child Adolesc Psychiatry. 2001;10:230-239. 40. Bauermeister JJ, Canino G, Polanczyk G, Rohde LA. ADHD across cultures: Is there evidence for a bidimensional organization of symptoms? J Clin Child Adolesc Psychol. 2010;39:362-372.
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ACCEPTED MANUSCRIPT 41. Laubjerg M, Christensen AM, Petersson B. Psychiatric status among stepchildren and domestic and international adoptees in denmark. A comparative nationwide register-based study. Scand J Public Health. 2009;37:604-612.
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Table 1. Incidence Rate Ratios (IRR) of Becoming a Parent for the First, Second, Third, Fourth, and Fifth Time for Individuals With Attention-Deficit/Hyperactivity Disorder (ADHD) Compared to Individuals Without ADHD BIRTHS/IRR
ADHD
0 → 1. Child
No. of births IRR (95% CI)
570 0.70 (0.64-0.76)
682,947 1.00 (reference)
1. → 2. Child
No. of births IRR (95% CI)
250 0.50 (0.44-0.57)
518,385 1.00 (reference)
2. → 3. Child
No. of births IRR (95% CI)
108 0.88 (0.73-1.06)
168,662 1.00 (reference)
3. → 4. Child
No. of births IRR (95% CI)
35 1.03 (0.74-1.43)
33,891 1.00 (reference)
4. → 5. Child
No. of births IRR (95% CI)
18 1.67 (1.05-2.65)
6,569 1.00 (reference)
MALES
BIRTHS/IRR
ADHD
NO ADHD
0 → 1. Child
No. of births IRR (95% CI)
1,106 0.56 (0.53-0.60)
603,003 1.00 (reference)
1. → 2. Child
No. of births IRR (95% CI)
495 0.53 (0.49-0.58)
436,067 1.00 (reference)
No. of births IRR (95% CI)
183 0.98 (0.85-1.14)
142,813 1.00 (reference)
No. of births IRR (95% CI)
67 1.49 (1.17-1.90)
29,907 1.00 (reference)
No. of births IRR (95% CI)
22 1.29 (0.85-1.96)
5,908 1.00 (reference)
4. → 5. Child
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3. → 4. Child
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2. → 3. Child
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FEMALES
NO ADHD
Figure 1. Incidence rate ratios (IRRs) for parenthood (first child) stratified by age group for females (top) and males (bottom) with attention-deficit/hyperactivity disorder (ADHD) compared to individuals without ADHD. Note: Error bars represent 95% CIs. Table 2. Mean Number of Children at Ages 20, 25, 30, 35 and 40 for Females and Males With and Without Attention-Deficit/Hyperactivity Disorder (ADHD)
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INDIVIDUALS/MEAN
ADHD
NO ADHD
20 years
No. of individuals Mean no of children (95%CI)
2,021 0.07 (0.05-0.08)
1,052,595 0.04 (0.04-0.04)*
25 years
No. of individuals Mean no of children (95%CI)
956 0.45 (0.40-0.49)
893,876 0.33 (0.33-0.33)*
30 years
No. of individuals Mean no of children (95%CI)
622 0.98 (0.89-1.07)
758,100 1.00 (1.00-1.01)
35 years
No. of individuals Mean no of children (95%CI)
490 1.65 (1.53-1.77)
619,602 1.63 (1.62-1.63)
40 years
No. of births Mean no of children (95%CI)
395 1.83 (1.69-1.96)
458,659 1.88 (1.88-1.89)
MALES
INDIVIDUALS/MEAN
ADHD
NO ADHD
20 years
No. of individuals Mean no of children (95%CI)
5,812 0.02 (0.02-0.03)
1,101,576 0.01 (0.01-0.01)*
25 years
No. of individuals Mean no of children (95%CI)
2,854 0.19 (0.18-0.21)
936,089 0.14 (0.14-0.15)*
30 years
No. of births Mean no of children (95%CI)
1,600 0.52 (0.48-0.56)
792,092 0.62 (0.62-0.62)*
35 years
No. of births Mean no of children (95%CI)
1,132 0.90 (0.83-0.96)
644,438 1.24 (1.24-1.24)*
40 years
No. of births Mean no of children (95%CI)
786 1.12 (1.02-1.21)
474,863 1.59 (1.59-1.59)*
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FEMALES
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Note: * Statistically significant difference (p<.05) in the mean number of children for females/males with and without ADHD.
Figure S1. Incidence rate ratios (IRRs) for parenthood (first child) stratified by age group for females and males with attention-deficit/hyperactivity disorder (ADHD) compared to individuals without ADHD (adjusted for potential confounders). Note: Error bars represent 95% CIs. Potential confounders were adjusted for calendar year, age of the cohort members, paternal (father of the cohort member) history of mental disorder, maternal (mother of the cohort member) history of mental disorders, paternal education level, maternal education level, paternal occupation, maternal occupation, oppositional defiant disorder or conduct disorder of the cohort members, substance use disorder of the cohort members, bipolar disorder of the cohort members, and schizophrenia of the cohort members.
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Table S1. Incidence Rate Ratios (IRR) of Becoming a Parent for the First, Second, Third, Fourth, and Fifth Time for Individuals With Attention-Deficit/Hyperactivity Disorder (ADHD) Compared to Individuals Without ADHD (Adjusted for Potential Confoundersa) FEMALES BIRTHS/IRR ADHD NO ADHD 0 → 1. Child No. of births 570 682,947 IRR (95% CI) 0.79 (0.73-0.86) 1.00 (reference) 1. → 2. Child No. of births 250 518,385 IRR (95% CI) 0.59 (0.52-0.67) 1.00 (reference) 2. → 3. Child No. of births 108 168,662 IRR (95% CI) 0.85 (0.71-1.03) 1.00 (reference) 3. → 4. Child No. of births 35 33,891 IRR (95% CI) 0.92 (0.66-1.29) 1.00 (reference) 4. → 5. Child No. of births 18 6,569 IRR (95% CI) 1.52 (0.95-2.43) 1.00 (reference) MALES BIRTHS/IRR ADHD NO ADHD 0 → 1. Child No. of births 1,106 603,003 IRR (95% CI) 0.78 (0.73-0.82) 1.00 (reference) 1. → 2. Child No. of births 495 436,067 IRR (95% CI) 0.71 (0.65-0.78) 1.00 (reference) 2. → 3. Child No. of births 183 142,813 IRR (95% CI) 1.06 (0.91-1.23) 1.00 (reference) 3. → 4. Child No. of births 67 29,907 IRR (95% CI) 1.42 (1.10-1.81) 1.00 (reference) 4. → 5. Child No. of births 22 5,908 IRR (95% CI) 1.28 (0.83-1.96) 1.00 (reference) Note: a Adjusted for calendar year, age of the cohort members, paternal (father of the cohort member) history of mental disorder, maternal (mother of the cohort member) history of mental disorders, paternal education level, maternal education level, paternal occupation, maternal occupation, oppositional defiant disorder, or conduct disorder of the cohort members, substance use disorder of the cohort members, bipolar disorder of the cohort members, and schizophrenia of the cohort members.
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Table S2. Incidence Rate Ratios (IRRs) for Parenthood (First Child) Stratified by Age Group for Females and Males With Attention-Deficit/Hyperactivity Disorder (ADHD; Exclusively Based on International Classification of Diseases– 10th Revision [ICD-10] Diagnoses) Compared to Individuals Without ADHD Age (y) Sex and ADHD Status Risk Years Children (n) Rate (1000 yrs) IRR (95% CI) 12-19 Females with ADHD 17599 105 5.966 1.91 (1.58-2.32) 12-19 Females without ADHD 3871017 9,786 2.528 1.00 (reference) 12-19 Males with ADHD 62757 116 1.848 2.05 (1.71-2.47) 12-19 Males without ADHD 4037508 3,004 0.744 1.00 (reference) 20-24 Females with ADHD 5079 230 45.286 1.33 (1.17-1.51) 20-24 Females without ADHD 1269447 40,050 31.549 1.00 (reference) 20-24 Males with ADHD 15465 340 21.985 1.32 (1.19-1.47) 20-24 Males without ADHD 1393617 21,622 15.515 1.00 (reference) 25+ Females with ADHD 1580 64 40.509 0.36 (0.29-0.47) 25+ Females without ADHD 509115 55,499 109.011 1.00 (reference) 25+ Males with ADHD 4959 208 41.943 0.58 (0.50-0.66) 25+ Males without ADHD 644142 46,018 71.441 1.00 (reference) Note: The analysis is based on data from a cohort consisting of all individuals born from January 1, 1980 to December 31, 2001 with follow-up (regarding parenthood from January 1, 1992 to December 31, 2012). The cohort members were followed from January 1, 1992 or from their 12th birthday, whichever came last, until the first of the following events: childbirth, emigration, death, loss to follow-up or January 1, 2013. The data was analyzed by means of Poisson regression (survival analysis) using the logarithm of the number of person-years at risk as an offset variable. Incidence rates for parenthood (first child) were compared between those having developed ADHD with those not having developed ADHD, by calculating IRRs, which can be interpreted as relative risks. The analyses were stratified by sex and adjusted for calendar year (1 year strata [time dependent]), and the age of the cohort members (1 year strata [time
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dependent]). The 95% CIs for the IRRs and the p-values were based on likelihood ratio tests with .05 as the threshold for statistical significance. All analyses were carried out using SAS version 9.4 (SAS Institute Inc., Cary, NC).
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7 6 5 4
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3
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2
0 17 to 19
20 to 24
25 to 29
30 to 34
35 +
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30 to 34
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35 to 39
40 +
S0890-8567(17)30205-8
DOI:
10.1016/j.jaac.2017.05.003
Reference:
JAAC 1753
To appear in:
Journal of the American Academy of Child & Adolescent Psychiatry
Received Date: 23 January 2017 Revised Date:
5 April 2017
Accepted Date: 4 May 2017
Please cite this article as: Østergaard SD, Dalsgaard S, Faraone SV, Munk-Olsen T, Laursen TM, Teenage Parenthood and Birth Rates for Individuals With and Without Attention-Deficit/Hyperactivity Disorder: A Nationwide Cohort Study, Journal of the American Academy of Child & Adolescent Psychiatry (2017), doi: 10.1016/j.jaac.2017.05.003. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT Teenage Parenthood and Birth Rates for Individuals With and Without Attention-Deficit/Hyperactivity Disorder: A Nationwide Cohort Study RH = Teenage Parenthood in ADHD Søren D. Østergaard, MD, PhD, Søren Dalsgaard, MD, PhD, Stephen V. Faraone, PhD, Trine Munk-Olsen, PhD, Thomas M. Laursen, PhD
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Supplemental material cited in this article is available online. Accepted May 5, 2017
This article was reviewed under and accepted by Ad Hoc Editor James F. Leckman, MD.
Dr. Østergaard is with Aarhus University Hospital, Aarhus, Denmark; The Psychosis Research Unit, Aarhus University Hospital, Risskov, Denmark; and The Lundbeck Foundation Initiative for Integrative Psychiatric
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Research (iPSYCH), Aarhus. Dr. Dalsgaard is with The National Centre for Register-Based Research, Aarhus University, iPSYCH, and Hospital of Telemark, Kragerø, Norway. Dr. Faraone is with State
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University of New York (SUNY) Upstate Medical University, Syracuse, and The K.G. Jebsen Centre for Neuropsychiatric Disorders, University of Bergen, Bergen, Norway. Dr. Munk-Olsen is with The National Centre for Register-Based Research, and iPSYCH. Dr. Laursen is with The National Centre for RegisterBased Research, iPSYCH, and The Centre for Integrated Register-based Research at Aarhus University (CIRRAU), Aarhus.
The study is supported by a grant from the Lundbeck Foundation. The funding body had no influence on the
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study design; the collection, analysis and interpretation of data; writing of the report; and the decision to submit the article for publication.
Dr. Østergaard is supported by a grant from the Lundbeck Foundation. Dr. Faraone is supported by the K.G. Jebsen Centre for Research on Neuropsychiatric Disorders, University of Bergen, Bergen, Norway, the European Union's Seventh Framework Programme for research, technological development and
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demonstration under grant agreement no 602805, the European Union's Horizon 2020 research and innovation programme under grant agreement No 667302, and NIMH grant 5R01MH101519.
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Dr. Laursen served as the statistical expert for this research. Disclosure: In the past 2 years, Dr. Faraone has received income, potential income, travel expenses, continuing education support, and/or research support from Lundbeck, Rhodes, Arbor, KenPharm, Ironshore, Shire, Akili Interactive Labs, CogCubed, Alcobra, VAYA, Sunovion, Genomind and Neurolifesciences. With his institution, he has US patent US20130217707 A1 for the use of sodium-hydrogen exchange inhibitors in the treatment of ADHD. In previous years, he has received support from Shire, Neurovance, Alcobra, Otsuka, McNeil, Janssen, Novartis, Pfizer, and Eli Lilly and Co. He has received royalties from books published by Guilford Press (Straight Talk about Your Child’s Mental Health), Oxford University Press (Schizophrenia: The Facts), and Elsevier (ADHD: Non-Pharmacologic Interventions). He is principal investigator of www.adhdinadults.com. Drs. Østergaard, Dalsgaard, Munk-Olsen, and Laursen report no biomedical financial interests or potential conflicts of interest.
ACCEPTED MANUSCRIPT Correspondence to Søren Dinesen Østergaard, MD, PhD, Psychosis Research Unit, Aarhus University,
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Hospital, Risskov, Skovagervej 2, 8240 Risskov; email: [email protected]
ACCEPTED MANUSCRIPT ABSTRACT Objective: Prior studies have established that attention-deficit/hyperactivity disorder (ADHD) is associated with risky sexual behavior, but it remains unknown whether individuals with ADHD are also more likely to become parents while being teenagers. This aspect is clinically relevant since
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teenage parenthood is associated with adverse outcomes for both parents and children. Therefore, the main aim of this study was to investigate whether individuals with ADHD are more likely to become teenage parents compared to individuals without ADHD.
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Method: This is a historical prospective cohort study based on nationwide data from Danish registers. The cohort consisted of all individuals (N=2,698,052) born in Denmark from January 1st
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1960 to December 31st 2001. The association between ADHD (n=27,479 cases) and parenthood (first child) in age intervals 12-16, 17-19, 20-24, 25-29, 30-34, 35-39, and 40+ years was investigated by means of Poisson regression and expressed as incidence rate ratios (IRRs) with accompanying 95% CIs. The IRRs can be interpreted as relative risks.
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Results: Compared to individuals without ADHD, those with ADHD were significantly more likely to become parents at age 12-15 (IRR for females: 3.62 [95%CI 2.14-6.13] and for males: 2.30
[95%CI 1.90-2.70]).
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[95%CI 1.27-4.17]) and at age 16-19 (IRR for females: 1.94 [95%CI 1.62-2.33] and for males: 2.27
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Conclusion: Individuals with ADHD are significantly more likely to become teenage parents compared to individuals without ADHD. Therefore, it may be appropriate to target this group with an intervention program including sexual education and contraceptive counseling. Key words: Attention-deficit/hyperactivity disorder; Parenthood; Birth rate
INTRODUCTION Attention-deficit/hyperactivity disorder (ADHD) is a neurodevelopmental disorder that affects approximately 5% of children and adolescents.1 The inattentive and hyperactive-impulsive
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ACCEPTED MANUSCRIPT symptoms of ADHD place a significant burden on those affected in terms of difficulties in interpersonal relationships,2 poor educational attainment,3 decreased lifetime earnings,4 criminal behavior,5,6 accidents,7 comorbid substance use disorders,8 and increased risk of premature mortality.9
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Another feature of ADHD, which is likely to have adverse consequences, is risky sexual behavior. This aspect has received some attention from researchers in recent years. For instance, in a sample of 115 adolescents (aged 12-17, 84% males) involved in the US Juvenile Drug Court,
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Sarver and colleagues showed that ADHD was associated with risky sexual behavior among those with comorbid oppositional defiant disorder (ODD) or conduct disorder (CD). This association was
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primarily mediated by problematic alcohol/marijuana use.10 Similarly, in a cohort of young adults (aged 19-25, 91% males) followed for at least 13 years, Barkley et al. reported that hyperactive individuals (n=149) were significantly younger at first sexual intercourse, had more sex partners, and were significantly more likely to have been involved in a pregnancy, compared to a community
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control group (n=72).11 In a study of college students, Huggins et al. showed that females with ADHD (n=24, mean age= 20 years, SD=1) were more likely to have sex without using a condom compared to females without ADHD (n=28, mean age 19 years, SD=1), males without ADHD
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(n=20, mean age=19 years, SD=1) and males with ADHD (n=20, mean age=20 years, SD=2).12 To
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our knowledge, Huggins et al. is the only study reporting data regarding risky sexual behavior specifically in females with ADHD. Finally, in a sample of 175 young men with ADHD and 111 controls (aged 18-26), Flory and colleagues reported that childhood ADHD predicted earlier initiation of sexual activity, more casual sex, more sexual partners, and more pregnancies.13 Risky sexual behavior may be associated with a series of adverse outcomes, such as sexually transmitted diseases, non-spontaneous abortions, and teenage parenthood. In this study, we focused on the latter, namely whether individuals with ADHD are more likely to become parents while being teenagers. This has not been investigated previously and is of significant interest due to the
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ACCEPTED MANUSCRIPT substantial literature documenting that teenage parenthood is associated with a significantly increased risk of adverse outcomes for both the young parents (low educational attainment, single habitation, welfare dependency, and disability pension)14,15 and their children (preterm birth, low birth weight, low Apgar scores, increased neonatal mortality, low educational achievement, low
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income and low life satisfaction).16-19 Furthermore, we investigated whether individuals with
following research questions were addressed: When compared to individuals without ADHD:
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ADHD have more children compared to individuals without ADHD over time.20 Specifically, the
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I) … are individuals with ADHD more likely to become parents while being teenagers? II) … are individuals with ADHD more likely to become parents in general? III) … are individuals with ADHD who have children more likely to have many children? IV) … do individuals with ADHD on average have more or fewer children? METHOD
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Cohort
This is a population-based historical prospective cohort study. The dataset used in the study was obtained by register linkage via the unique personal registration numbers, which are assigned to
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all Danes at the time of birth and registered in the Danish Civil Registration System.21 The cohort
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was defined as all individuals born in Denmark from January 1st 1960 to December 31st 2001 who were alive and residing in Denmark on January 1st 1980 and/or at their 12th birthday, whichever came last. Based on the observation that some individuals in the cohort had already become parents by the age of 12, we decided to include the 12-year-olds in our definition of teenagers (i.e., age 1219). Definition of Parenthood Consistent with a prior Danish study of the reproductive pattern in individuals with mental disorders,22 parenthood was defined via link to a child born in Denmark in the Danish Civil
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ACCEPTED MANUSCRIPT Registration System.21 Definition of ADHD Individuals having received an International Classification of Diseases–8th Revision (ICD8)23 diagnosis of 308.01 or an International Classification of Diseases–10th Revision (ICD-10)24
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diagnosis of F90.x or F98.8 following either inpatient or outpatient treatment at psychiatric, pediatric or neurological departments in Denmark9 were defined as ADHD cases from the date the diagnosis was assigned. Diagnostic data regarding ADHD for the cohort members was extracted
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from the Danish Psychiatric Central Research Register (DPCRR)25,26 and from the Danish National Patient Register (DNPR).27 In these two registers, the ICD-8 was used as diagnostic reference until
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January 1st 1994, when it was replaced by the ICD-10. Until December 31st 1994, only diagnoses assigned following inpatient treatment were registered in the DPCRR. From January 1st 1995 and onwards, diagnoses assigned following outpatient treatment were included as well. Statistics and Follow-Up for Each Research Question
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The data was analyzed by means of Poisson regression (survival analysis) using the logarithm of the number of person-years at risk as an offset variable. This method approximates a Cox regression28 and takes the length of follow-up for each cohort member into account. Incidence
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rates were compared between those having developed ADHD with those not having developed
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ADHD, by calculating incidence rate ratios (IRRs), which can be interpreted as relative risks. All IRRs were stratified by sex and adjusted for calendar year (1 year strata [time dependent]), and the age of the cohort members (1 year strata [time dependent]). The 95% CIs for the IRRs and the p-values were based on likelihood ratio tests with .05 as the threshold for statistical significance. All analyses were carried out using SAS version 9.4 (SAS Institute Inc, Cary, NC). The exact definition of the cohort and the follow-up period varied depending on the nature of the research question. Below, these variations are specified for each of the four research questions:
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ACCEPTED MANUSCRIPT I) … are individuals with ADHD more likely to become parents while being teenagers? To answer this question the cohort members were followed from January 1st 1980 or from their 12th birthday, whichever came last. The follow-up ended at childbirth, emigration, death, loss to followup, or January 1, 2013, whichever came first. Specifically, we calculated IRRs for having a child
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within the following age intervals among females: 12-16, 17-19, 20-24, 25-29, 30-34, 35+ and for the following intervals among males: 12-16, 17-19, 20-24, 25-29, 30-34, 35-39, 40+.
II) … are individuals with ADHD more likely to become parents in general? For this research
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question the cohort members were followed from January 1, 1980 or from their 12th birthday,
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whichever came last. The follow-up ended at childbirth, emigration, death, loss to follow-up, or January 1, 2013, whichever came first. Since we followed the eldest cohort members up to the age of 53 years, the IRRs calculated in this analysis roughly reflect the likelihood of females and males diagnosed with ADHD becoming parents, compared to those without ADHD. III) … are individuals with ADHD who have children more likely to have many children? Here
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we calculated the IRRs for progression from having child number one to child number two, from child number two to child number three, from child number three to child number four, and from child number four to child number five. In these analyses, we followed up individuals from the birth
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of their first, second, third, and fourth child, respectively. The follow-up ended at the subsequent
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childbirth, emigration, death, loss to follow-up, or January 1, 2013, whichever came first. IV) … do individuals with ADHD on average have more or fewer children? To answer this question, we calculated the average number of children that females and males with and without ADHD respectively had had by the ages of 20, 25, 30, and 40 years. Finally, to assess whether the answers to the analytical research questions I-III (research question IV is of descriptive nature) were driven by confounding rather than by ADHD, we repeated the analyses described above, while adding adjustment for the following covariates: paternal (father of the cohort members) history of mental disorders (with the following levels:
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ACCEPTED MANUSCRIPT unknown father, no contact with psychiatric services, any diagnosis assigned by psychiatric services (ICD-8 diagnoses 290-315, and ICD-10 diagnoses F00-F99) apart from bipolar disorder or schizophrenia (ICD-8 diagnoses 295.x9 [excluding 295.79], 296.19, 296.39, 298.19, and ICD-10 diagnoses F20, F30, F31, bipolar disorder or schizophrenia),25 maternal (mother of the cohort
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members) history of mental disorders (identical levels as for the father), paternal education level (with the following levels: unknown father, unknown education level, compulsory schooling, highschool/technical education/short-cycle higher education, medium-cycle higher education, long-
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cycle higher education),29 maternal education level (identical levels as the father), paternal
occupation status (with the following levels: unknown father, unknown occupation status, under-
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educated, employed, unemployed, outside the workforce),30 maternal occupation (identical levels as the father), ODD or CD of the cohort members (ICD-8 diagnoses 308.03 and 308.04, and ICD-10 diagnoses F91.x and F90.1), substance use disorder (SUD) of the cohort members (ICD-8 diagnoses 291.x9, 294.39, 303.x9, 303.20, 303.28, 303.90, 304.x9, and ICD-10 diagnoses F10–F19), bipolar
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disorder of the cohort members (ICD-8 diagnoses 296.19, 296.39, 298.19, and ICD-10 diagnoses F30-F31), and schizophrenia of the cohort members (ICD-8 diagnoses 295.x9 [excluding 295.79], and ICD-10 diagnosis F20). Parental mental disorder and comorbid ODD/CD, SUD, bipolar
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disorder, or schizophrenia were treated as time-dependent covariates, while parental education level
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and occupation status were assessed at age 15 of the cohort members (or the year closest to age 15 with available data). We did not include the education level and occupation status of the cohort members in the adjusted analyses as deviations from the general population on these parameters are likely to be on the causal path from ADHD to a specific reproductive pattern rather than representing confounders of this association. RESULTS The established cohort comprised 2,698,052 individuals (1,384,334 males and 1,313,718 females) of which 27,479 (20,093 males and 7,386 females) had received an ADHD diagnosis
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ACCEPTED MANUSCRIPT during follow-up. The results pertaining to the three analytical research questions (I-III) and the descriptive research question (IV) are as follows: I) … are individuals with ADHD more likely to become parents while being teenagers? The IRRs for becoming a parent within various age intervals are shown in Figure 1 (stratified by sex).
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Individuals with ADHD were significantly more likely to become parents at ages 12-15 (IRR for females: 3.62 [95%CI 2.14-6.13] and for males: 2.30 [95%CI 1.27-4.17]) and at ages 16-19 (IRR for females: 1.94 [95%CI 1.62-2.33] and for males: 2.27 [95%CI 1.90-2.70]). Conversely,
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individuals with ADHD were significantly less likely to become parents at 25 years and older.
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Figure 1 approximately here
II) … are individuals with ADHD more likely to become parents in general? The IRRs for becoming a parent were 0.56 (95%CI 0.53-0.60) for males with ADHD and 0.70 (95%CI 0.64-0.76) for females, compared to the reference value (1.00) for males and females without ADHD. Thus,
females without ADHD.
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both males and females with ADHD were significantly less likely to become parents than males and
III) … are individuals with ADHD who have children more likely to have many children? The IRRs for individuals with ADHD progressing from having child number one to child number two,
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from child number two to child number three, from child number three to child number four, and
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from child number four to child number five are shown in Table 1. Compared to males without ADHD, males with ADHD were significantly less likely to progress from having child number one to child number two, but significantly more likely to progress from having child number three to number four. The pattern was similar for females with ADHD who were significantly less likely to progress from having child number one to child number two, but significantly more likely to progress from having child number four to number five. Table 1 approximately here IV) … do individuals with ADHD on average have more or fewer children? The average number
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ACCEPTED MANUSCRIPT of children that females and males with and without ADHD, respectively, had had at the ages of 20, 25, 30, 35, and 40 years is shown in Table 2. These results show that males with ADHD had had significantly more children than those without ADHD by the ages of 20 and 25, but significantly fewer by the ages of 30, 35, and 40 years. For females, those with ADHD had on average
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significantly more children than those without ADHD by the ages of 20 and 25 years, while the number of children by the ages of 30, 35, and 40 was roughly the same for the two groups. Table 2 approximately here
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The significant differences reported for the analytical research questions I-III withstood
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adjustment for paternal history of mental disorders, maternal history of mental disorders, paternal education level, maternal education level, paternal occupation status, maternal occupation status, and comorbid ODD/CD, SUD, bipolar disorder, or schizophrenia of the cohort members (results reported in Table S1 and Figure S1, available online), with one exception: females with ADHD
adjusted analysis. DISCUSSION
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were not significantly more likely to progress from having child number four to number five in the
The results of this nationwide cohort study of 2,698,052 individuals show that individuals
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with ADHD (n=27,479) differed from those without ADHD (n=2,670,573) on all of the
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investigated aspects regarding the age of parenthood and birth rates. Compared to individuals without ADHD, those with ADHD I) are more likely to become parents while being teenagers, II) are less likely to become parents in general, III) are more likely to have many children (three or more for males and four or more for females) if they do become parents, and IV) have fewer children on average (only males). The adjusted analyses indicated that this pattern is likely to be a consequence of ADHD and not of confounding, except from the increased likelihood of females having many children if they do become parents, which was not significant after adjustment. To our knowledge, this study is the first to study the association between ADHD and the age at parenthood
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ACCEPTED MANUSCRIPT /number of births in a very large population-based cohort with follow-up covering virtually the entire reproductive life. Therefore, the results presented here are largely unprecedented and provide new knowledge on the consequences of ADHD. From a clinical perspective, the most important finding of this study is that individuals with
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ADHD are significantly more likely to become parents during their teenage years compared to individuals without ADHD (Figure 1). This is consistent with the finding by Barkley et al., who showed that being diagnosed with hyperactivity was associated with relatively early parenthood
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(mean age at follow-up = 20 years).11 This finding is of interest due to the substantial literature
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documenting that teenage parenthood is associated with a significantly increased risk of adverse outcomes for both the young parents (low educational attainment, single habitation, welfare dependency, and disability pension)14, 15 and their children (preterm birth, low birth weight, low Apgar scores, increased neonatal mortality, low educational achievement, low income, and low life satisfaction).16-19 These associations have been considered to be sufficiently strong and the outcome
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sufficiently adverse to merit preventive interventions to reduce teenage pregnancies.31-34 Our finding that individuals with ADHD are more likely to become parents during their teenage years indicates that it may be appropriate to target this group with a multifactorial program including
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sexual education and contraceptive counseling. Indeed, such initiatives may be of particular
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importance among those with ADHD, since parenting in general is known to be difficult for these individuals.35, 36 Being a teenage parent with ADHD is likely to be even more challenging. It would seem that such sexual education and contraceptive counseling should ideally be organized by the mental health professionals who are responsible for the diagnosis and treatment of ADHD, as they are likely to be able to address the issue in a timely manner. Otherwise, there is a substantial risk of intervening too late, only being able to address the risk of repeat teenage pregnancies.33 We are not aware of any evidence-based intervention programs addressing this challenge in relation to ADHD, but when designing such an initiative, experience from the successful young parent program to
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ACCEPTED MANUSCRIPT reduce repeat teen pregnancy, described by Omar et al,33 could be used as a source of inspiration. The other findings of our study regarding the reproductive rates of individuals with ADHD can be summarized as follows: many have no children, yet few have many children. Indeed, the overall likelihood for individuals with ADHD to become parents was significantly lower than that
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of individuals without ADHD. This is consistent with our prior findings from schizophrenia, bipolar disorder, and major depression,22 indicating that mental disorders in general are associated with a decreased likelihood of becoming a parent. However, when taking a closer look at the individuals
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with ADHD who did become parents, we observed that they were more likely to have more
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children than those without ADHD. As a consequence, the mean number of children born to females with ADHD was similar to that of females without ADHD (at the age of 30, 35, and 40). The males with ADHD did not, however, “catch up” in this manner as their mean number of offspring was significantly lower than for males without ADHD (at the age of 30, 35, and 40). While this finding may be partly explained by differential registration of paternities (more
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unregistered paternities among males with ADHD compared to males without ADHD – perhaps particularly pronounced for young fathers), the difference is so substantial that it is unlikely to be fully accounted for by unregistered paternities. Therefore, this result supports prior findings
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suggesting that, from a reproductive perspective, mental disorders have more severe consequences
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for males than for females.22,37 The reasons underlying this sex difference cannot be determined based on the data at hand, but it is likely to reflect that females have the ultimate say in whether a pregnancy should be carried to term or not. In other words, if a female with ADHD wants a child, she can, in most cases, make that decision when becoming pregnant. For a male with ADHD who wants to have a child, he will need a female partner who will have his child. The most significant limitation of this study is our use of a register-based definition of ADHD. The diagnoses in the registers providing data for this study are assigned as part of normal clinical practice and not necessarily based on standardized research interviews. However, the validity of the
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ACCEPTED MANUSCRIPT ADHD diagnoses has been found to be acceptable.38,39 The ICD-8 definition of ADHD is probably less reliable than the ICD-10 definition.38,39 Therefore, we conducted a sensitivity analysis in which we addressed the main research question (are individuals with ADHD more likely to become teenage parents compared to individuals without ADHD) in a restricted cohort consisting of
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individuals born from January 1, 1980 to December 31, 2001 and followed up regarding parenthood from January 1, 1994 to January 1, 2013. Within this cohort we only considered ICD-10 diagnoses of ADHD (diagnosed from January 1, 1994). The results of this strictly ICD-10-based analysis (see
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Table S2, available online) confirmed those of the ICD-8 + ICD-10-based analysis, as it showed
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that both males and females with ADHD were more likely to become teenage parents than their peers without ADHD. In addition to being an indirect confirmation of the validity of the ICD-8 definition of ADHD, this result also indicates that the association between ADHD and early parenthood has been relatively stable over the observation period covered by this study (January 1, 1980 to January 1, 2013).
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The register-based definition of ADHD also has implications for the external validity of our findings. This is due to the fact that psychiatrists and pediatricians in private practice, who diagnose and treat a minority of ADHD cases in Denmark, do not report diagnoses to the registers. Therefore,
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our results may not generalize to patients seen in these private practices. That being said, it is our
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impression that the differences in reproductive patterns between individuals with and without ADHD described in this article are likely to be generalizable to other settings and cultures as they seem to fit well with the core psychopathology of ADHD, which is relatively independent of these aspects.40
Another potential limitation is that parenthood is defined via the Civil Registration System (legal parenthood), which corresponds to biological parenthood in the vast majority of cases, but there may be some misclassifications – i.e., children, who have been adopted by stepparents etc. However, this is only of minor concern, as such adoptions are rare in Denmark.41
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ACCEPTED MANUSCRIPT In conclusion, the results of this nationwide cohort study show that, compared to individuals without ADHD, those with ADHD I) are more likely to become parents while being teenagers, II) are less likely to become parents in general, III) are more likely to have many children if they do become parents, and IV) have less children on average (only males). From a clinical perspective,
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the most important finding of our study is that individuals with ADHD are significantly more likely to become parents during their teenage years compared to individuals without ADHD. Since teenage parenthood is associated with a number of adverse outcomes for both parents and children,
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it may be of relevance to target this group with an intervention program (including sexual education
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and contraceptive counseling) to reduce the number of teenage pregnancies. REFERENCES
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Atten Disord. 2015;19:844-855.
3. Loe IM, Feldman HM. Academic and educational outcomes of children with ADHD. J Pediatr Psychol. 2007;32:643-654.
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4. Kotsopoulos N, Connolly MP, Sobanski E, Postma MJ. The fiscal consequences of ADHD in
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germany: A quantitative analysis based on differences in educational attainment and lifetime earnings. J Ment Health Policy Econ. 2013;16:27-33. 5. Dalsgaard S, Mortensen PB, Frydenberg M, Thomsen PH. Long-term criminal outcome of children with attention deficit hyperactivity disorder. Crim Behav Ment Health. 2013;23:86-98. 6. Marton I, Wiener J, Rogers M, Moore C. Friendship characteristics of children with ADHD. J Atten Disord. 2015;19:872-881. 7. Chang Z, Lichtenstein P, D'Onofrio BM, Sjolander A, Larsson H. Serious transport accidents in adults with attention-deficit/hyperactivity disorder and the effect of medication: A population-based
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9. Dalsgaard S, Ostergaard SD, Leckman JF, Mortensen PB, Pedersen MG. Mortality in children, adolescents, and adults with attention deficit hyperactivity disorder: A nationwide cohort study. Lancet. 2015;385:2190-2196.
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10. Sarver DE, McCart MR, Sheidow AJ, Letourneau EJ. ADHD and risky sexual behavior in
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14. Olausson PO, Haglund B, Weitoft GR, Cnattingius S. Teenage childbearing and long-term
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socioeconomic consequences: A case study in sweden. Fam Plann Perspect. 2001;33:70-74. 15. Fletcher JM, Wolfe BL. The effects of teenage fatherhood on young adult outcomes. Econ Inq. 2012;50:182-201.
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ACCEPTED MANUSCRIPT 18. Chen XK, Wen SW, Fleming N, Demissie K, Rhoads GG, Walker M. Teenage pregnancy and adverse birth outcomes: A large population based retrospective cohort study. Int J Epidemiol. 2007;36:368-373. 19. Igwegbe AO, Udigwe GO. Teenage pregnancy: Still an obstetric risk. J Obstet Gynaecol.
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20. Thagaard MS, Faraone SV, Sonuga-Barke EJ, Ostergaard SD. Empirical tests of natural selection-based evolutionary accounts of ADHD: A systematic review. Acta Neuropsychiatr.
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21. Pedersen CB. The danish civil registration system. Scand J Public Health. 2011;39:22-25. 22. Laursen TM, Munk-Olsen T. Reproductive patterns in psychotic patients. Schizophr Res. 2010;121:234-240.
23. Danish National Board of Health. Classification of diseases: Extended danish-latin version of the world health organization international statistical classification of diseases and related health
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problems, 8th revision. Copenhagen, Denmark: Danish National Board of Health; 1971. 24. World Health Organization. The ICD-10 classification of mental and behavioural disorders. diagnostic criteria for research. Geneva: WHO; 1993.
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25. Mors O, Perto GP, Mortensen PB. The danish psychiatric central research register. Scand J
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26. Munk-Jorgensen P, Ostergaard SD. Register-based studies of mental disorders. Scand J Public Health. 2011;39:170-174.
27. Lynge E, Sandegaard JL, Rebolj M. The danish national patient register. Scand J Public Health. 2011;39:30-33. 28. Andersen PK, Borgen Ø, Gill RD, Keiding N. Statistical models based on counting processes. New York: Springer-Verlag; 1993. 29. Jensen VM, Rasmussen AW. Danish education registers. Scand J Public Health. 2011;39:91-4.
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32. Lavin C, Cox JE. Teen pregnancy prevention: Current perspectives. Curr Opin Pediatr. 2012;24:462-469.
33. Omar HA, Fowler A, McClanahan KK. Significant reduction of repeat teen pregnancy in a
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comprehensive young parent program. J Pediatr Adolesc Gynecol. 2008;21:283-287.
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34. Wellings K, Palmer MJ, Geary RS, et al. Changes in conceptions in women younger than 18 years and the circumstances of young mothers in england in 2000-12: An observational study. Lancet. 2016;388:586-595.
35. Murray C, Johnston C. Parenting in mothers with and without attention-deficit/hyperactivity disorder. J Abnorm Psychol. 2006;115:52-61.
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36. Williamson D, Johnston C, Noyes A, Stewart K, Weiss MD. Attention-deficit/hyperactivity disorder symptoms in mothers and fathers: Family level interactions in relation to parenting. J Abnorm Child Psychol. 2017;45:485-500.
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37. McGrath JJ, Hearle J, Jenner L, Plant K, Drummond A, Barkla JM. The fertility and fecundity
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of patients with psychoses. Acta Psychiatr Scand. 1999;99:441-446. 38. Linnet KM, Wisborg K, Secher NJ, et al. Coffee consumption during pregnancy and the risk of hyperkinetic disorder and ADHD: A prospective cohort study. Acta Paediatr. 2009;98:173-179. 39. Dalsgaard S, Hansen N, Mortensen PB, Damm D, Thomsen PH. Reassessment of ADHD in a historical cohort of children treated with stimulants in the period 1969-1989. Eur Child Adolesc Psychiatry. 2001;10:230-239. 40. Bauermeister JJ, Canino G, Polanczyk G, Rohde LA. ADHD across cultures: Is there evidence for a bidimensional organization of symptoms? J Clin Child Adolesc Psychol. 2010;39:362-372.
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ACCEPTED MANUSCRIPT 41. Laubjerg M, Christensen AM, Petersson B. Psychiatric status among stepchildren and domestic and international adoptees in denmark. A comparative nationwide register-based study. Scand J Public Health. 2009;37:604-612.
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Table 1. Incidence Rate Ratios (IRR) of Becoming a Parent for the First, Second, Third, Fourth, and Fifth Time for Individuals With Attention-Deficit/Hyperactivity Disorder (ADHD) Compared to Individuals Without ADHD BIRTHS/IRR
ADHD
0 → 1. Child
No. of births IRR (95% CI)
570 0.70 (0.64-0.76)
682,947 1.00 (reference)
1. → 2. Child
No. of births IRR (95% CI)
250 0.50 (0.44-0.57)
518,385 1.00 (reference)
2. → 3. Child
No. of births IRR (95% CI)
108 0.88 (0.73-1.06)
168,662 1.00 (reference)
3. → 4. Child
No. of births IRR (95% CI)
35 1.03 (0.74-1.43)
33,891 1.00 (reference)
4. → 5. Child
No. of births IRR (95% CI)
18 1.67 (1.05-2.65)
6,569 1.00 (reference)
MALES
BIRTHS/IRR
ADHD
NO ADHD
0 → 1. Child
No. of births IRR (95% CI)
1,106 0.56 (0.53-0.60)
603,003 1.00 (reference)
1. → 2. Child
No. of births IRR (95% CI)
495 0.53 (0.49-0.58)
436,067 1.00 (reference)
No. of births IRR (95% CI)
183 0.98 (0.85-1.14)
142,813 1.00 (reference)
No. of births IRR (95% CI)
67 1.49 (1.17-1.90)
29,907 1.00 (reference)
No. of births IRR (95% CI)
22 1.29 (0.85-1.96)
5,908 1.00 (reference)
4. → 5. Child
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3. → 4. Child
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2. → 3. Child
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FEMALES
NO ADHD
Figure 1. Incidence rate ratios (IRRs) for parenthood (first child) stratified by age group for females (top) and males (bottom) with attention-deficit/hyperactivity disorder (ADHD) compared to individuals without ADHD. Note: Error bars represent 95% CIs. Table 2. Mean Number of Children at Ages 20, 25, 30, 35 and 40 for Females and Males With and Without Attention-Deficit/Hyperactivity Disorder (ADHD)
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INDIVIDUALS/MEAN
ADHD
NO ADHD
20 years
No. of individuals Mean no of children (95%CI)
2,021 0.07 (0.05-0.08)
1,052,595 0.04 (0.04-0.04)*
25 years
No. of individuals Mean no of children (95%CI)
956 0.45 (0.40-0.49)
893,876 0.33 (0.33-0.33)*
30 years
No. of individuals Mean no of children (95%CI)
622 0.98 (0.89-1.07)
758,100 1.00 (1.00-1.01)
35 years
No. of individuals Mean no of children (95%CI)
490 1.65 (1.53-1.77)
619,602 1.63 (1.62-1.63)
40 years
No. of births Mean no of children (95%CI)
395 1.83 (1.69-1.96)
458,659 1.88 (1.88-1.89)
MALES
INDIVIDUALS/MEAN
ADHD
NO ADHD
20 years
No. of individuals Mean no of children (95%CI)
5,812 0.02 (0.02-0.03)
1,101,576 0.01 (0.01-0.01)*
25 years
No. of individuals Mean no of children (95%CI)
2,854 0.19 (0.18-0.21)
936,089 0.14 (0.14-0.15)*
30 years
No. of births Mean no of children (95%CI)
1,600 0.52 (0.48-0.56)
792,092 0.62 (0.62-0.62)*
35 years
No. of births Mean no of children (95%CI)
1,132 0.90 (0.83-0.96)
644,438 1.24 (1.24-1.24)*
40 years
No. of births Mean no of children (95%CI)
786 1.12 (1.02-1.21)
474,863 1.59 (1.59-1.59)*
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Note: * Statistically significant difference (p<.05) in the mean number of children for females/males with and without ADHD.
Figure S1. Incidence rate ratios (IRRs) for parenthood (first child) stratified by age group for females and males with attention-deficit/hyperactivity disorder (ADHD) compared to individuals without ADHD (adjusted for potential confounders). Note: Error bars represent 95% CIs. Potential confounders were adjusted for calendar year, age of the cohort members, paternal (father of the cohort member) history of mental disorder, maternal (mother of the cohort member) history of mental disorders, paternal education level, maternal education level, paternal occupation, maternal occupation, oppositional defiant disorder or conduct disorder of the cohort members, substance use disorder of the cohort members, bipolar disorder of the cohort members, and schizophrenia of the cohort members.
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Table S1. Incidence Rate Ratios (IRR) of Becoming a Parent for the First, Second, Third, Fourth, and Fifth Time for Individuals With Attention-Deficit/Hyperactivity Disorder (ADHD) Compared to Individuals Without ADHD (Adjusted for Potential Confoundersa) FEMALES BIRTHS/IRR ADHD NO ADHD 0 → 1. Child No. of births 570 682,947 IRR (95% CI) 0.79 (0.73-0.86) 1.00 (reference) 1. → 2. Child No. of births 250 518,385 IRR (95% CI) 0.59 (0.52-0.67) 1.00 (reference) 2. → 3. Child No. of births 108 168,662 IRR (95% CI) 0.85 (0.71-1.03) 1.00 (reference) 3. → 4. Child No. of births 35 33,891 IRR (95% CI) 0.92 (0.66-1.29) 1.00 (reference) 4. → 5. Child No. of births 18 6,569 IRR (95% CI) 1.52 (0.95-2.43) 1.00 (reference) MALES BIRTHS/IRR ADHD NO ADHD 0 → 1. Child No. of births 1,106 603,003 IRR (95% CI) 0.78 (0.73-0.82) 1.00 (reference) 1. → 2. Child No. of births 495 436,067 IRR (95% CI) 0.71 (0.65-0.78) 1.00 (reference) 2. → 3. Child No. of births 183 142,813 IRR (95% CI) 1.06 (0.91-1.23) 1.00 (reference) 3. → 4. Child No. of births 67 29,907 IRR (95% CI) 1.42 (1.10-1.81) 1.00 (reference) 4. → 5. Child No. of births 22 5,908 IRR (95% CI) 1.28 (0.83-1.96) 1.00 (reference) Note: a Adjusted for calendar year, age of the cohort members, paternal (father of the cohort member) history of mental disorder, maternal (mother of the cohort member) history of mental disorders, paternal education level, maternal education level, paternal occupation, maternal occupation, oppositional defiant disorder, or conduct disorder of the cohort members, substance use disorder of the cohort members, bipolar disorder of the cohort members, and schizophrenia of the cohort members.
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Table S2. Incidence Rate Ratios (IRRs) for Parenthood (First Child) Stratified by Age Group for Females and Males With Attention-Deficit/Hyperactivity Disorder (ADHD; Exclusively Based on International Classification of Diseases– 10th Revision [ICD-10] Diagnoses) Compared to Individuals Without ADHD Age (y) Sex and ADHD Status Risk Years Children (n) Rate (1000 yrs) IRR (95% CI) 12-19 Females with ADHD 17599 105 5.966 1.91 (1.58-2.32) 12-19 Females without ADHD 3871017 9,786 2.528 1.00 (reference) 12-19 Males with ADHD 62757 116 1.848 2.05 (1.71-2.47) 12-19 Males without ADHD 4037508 3,004 0.744 1.00 (reference) 20-24 Females with ADHD 5079 230 45.286 1.33 (1.17-1.51) 20-24 Females without ADHD 1269447 40,050 31.549 1.00 (reference) 20-24 Males with ADHD 15465 340 21.985 1.32 (1.19-1.47) 20-24 Males without ADHD 1393617 21,622 15.515 1.00 (reference) 25+ Females with ADHD 1580 64 40.509 0.36 (0.29-0.47) 25+ Females without ADHD 509115 55,499 109.011 1.00 (reference) 25+ Males with ADHD 4959 208 41.943 0.58 (0.50-0.66) 25+ Males without ADHD 644142 46,018 71.441 1.00 (reference) Note: The analysis is based on data from a cohort consisting of all individuals born from January 1, 1980 to December 31, 2001 with follow-up (regarding parenthood from January 1, 1992 to December 31, 2012). The cohort members were followed from January 1, 1992 or from their 12th birthday, whichever came last, until the first of the following events: childbirth, emigration, death, loss to follow-up or January 1, 2013. The data was analyzed by means of Poisson regression (survival analysis) using the logarithm of the number of person-years at risk as an offset variable. Incidence rates for parenthood (first child) were compared between those having developed ADHD with those not having developed ADHD, by calculating IRRs, which can be interpreted as relative risks. The analyses were stratified by sex and adjusted for calendar year (1 year strata [time dependent]), and the age of the cohort members (1 year strata [time
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dependent]). The 95% CIs for the IRRs and the p-values were based on likelihood ratio tests with .05 as the threshold for statistical significance. All analyses were carried out using SAS version 9.4 (SAS Institute Inc., Cary, NC).
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7 6 5 4
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Ref
3
IRR
2
0 17 to 19
20 to 24
25 to 29
30 to 34
35 +
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20 to 24
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25 to 29
30 to 34
Ref IRR
35 to 39
40 +