- Email: [email protected]
Coital frequency and infertility: which male factors predict less frequent coitus among infertile couples?
ORIGINAL ARTICLES: INFERTILITY
Coital frequency and infertility: which male factors predict less frequent coitus among infertile couples? Nathan Perlis, M.D.,a,b,c Kirk C. Lo, M.D.,a,b,d Ethan D. Grober, M.D.,a,b Leia Spencer, R.N.,b and Keith Jarvi, M.D.a,b,d,e a Department of Surgery, Division of Urology, University of Toronto; b Mount Sinai Hospital; c Institute of Health Policy, Management and Evaluation and d Institute of Medical Science, University of Toronto; and e Samuel Lunenfeld Research Institute, Mount Sinai Hospital, Toronto, Ontario, Canada
Objective: To determine the coital frequency among infertile couples and which factors are associated with less frequent coitus. Design: Cross-sectional study. Setting: Tertiary-level male infertility clinic. Patient(s): A total of 1,298 infertile men. Intervention(s): Administration of computer-based survey, semen analysis, and serum hormone evaluation. Main Outcome Measure(s): Monthly coital frequency. Result(s): A total of 1,298 patients presented to clinic for infertility consultation and completed the computer-based survey. The median male age was 35 years (interquartile range [IQR] 32–39 years) and the median duration of infertility was 2 years (IQR 1–4 years) before consultation. Median monthly coital frequency was seven (IQR 5–10; range 0–40); 24% of couples were having intercourse %4 times per month. Overall, 0.6%, 2.7%, 4.8%, 5.8%, and 10.8% of the men reported having intercourse 0, 1, 2, 3, and 4 times per month, respectively. When simultaneously taking into account the influence of age, libido, erectile function, and semen volume on coital frequency, older patients had 1.05 times higher odds (per year of age) of less frequent coitus (odds ratio 1.05, 95% confidence interval 1.03–1.08). In addition, patients with better erectile function had 1.12 times higher odds (per point on Sexual Health Inventory for Men scale) of more frequent coitus (odds ratio 1.12, 95% confidence interval 1.09–1.18). Conclusion(s): Similar to the general population, most infertile couples report having coitus more than four times per month. Older male age and erectile dysfunction are independent risk factors for less frequent coitus among infertile men, which could have an impact on fertility. Coital frequency should be considered Use your smartphone in infertility assessments. (Fertil SterilÒ 2013;100:511–5. Ó2013 by American Society for to scan this QR code Reproductive Medicine.) and connect to the Key Words: Infertility, infertility assessment, intercourse Discuss: You can discuss this article with its authors and with other ASRM members at http:// fertstertforum.com/perlisn-intercourse-infertility-male-factor/
I
nfertility is caused by male and female factors with both organic and psychological etiologies (1). Prolonged infertility can be a psychosocial stress for the infertile couple leading to poor marital adjustment and decreased quality of life (2). Although some infertile couples report unsatisfactory sex lives (3), to our
knowledge, coital frequency has never been studied in men with infertility. To explore the question of how frequently infertile men were engaging in sex, we reviewed self-reported monthly coital frequency among a population of men presenting for evaluation of male factor infertility at a tertiary
Received November 2, 2012; revised April 8, 2013; accepted April 10, 2013; published online May 10, 2013. N.P. has nothing to disclose. K.C.L. has nothing to disclose. E.D.G. has nothing to disclose. L.S. has nothing to disclose. K.J. has nothing to disclose. Reprint requests: Keith Jarvi, M.D., Murray Koffler Urologic Wellness Centre, Joseph and Wolf Lebovic Building, Mount Sinai Hospital, 6th Floor, 60 Murray Street, Toronto, Ontario, M5T 3L9 Canada (E-mail: [email protected]). Fertility and Sterility® Vol. 100, No. 2, August 2013 0015-0282/$36.00 Copyright ©2013 American Society for Reproductive Medicine, Published by Elsevier Inc. http://dx.doi.org/10.1016/j.fertnstert.2013.04.020 VOL. 100 NO. 2 / AUGUST 2013
discussion forum for this article now.*
* Download a free QR code scanner by searching for “QR scanner” in your smartphone’s app store or app marketplace.
level male infertility clinic. We hypothesized that men presenting to an infertility clinic will be engaging in less frequent coitus than the general population. We were also interested in identifying factors that might predict which men are having less frequent coitus. We hypothesized that increased age, increased duration of infertility, low T and abnormal serum parameters would be associated with low coital frequency.
MATERIALS AND METHODS Data Source We collected and combined data on men from three unique sources at the 511
ORIGINAL ARTICLE: INFERTILITY Mount Sinai Hospital male infertility clinic in Toronto, Ontario, Canada from 2004–2010. Men were referred for investigation of male factor infertility by Reproductive Endocrinology Infertility specialists or family physicians and all of the men had an abnormal semen analysis and/or sperm assessment. Demographic data, referring physicians, treatment history, and risk factors for infertility were selfreported by men presenting for initial infertility assessment on a computer-based survey. These data were captured and linked with serum hormone profiles and semen analysis parameters if blood and semen collection was performed as part of patients’ medical evaluation. Institutional research ethics approval and patient-informed consent were obtained.
Exclusion Criteria Patients were excluded from analysis if survey data or linked serum and hormonal profile information was unavailable.
Outcome Monthly coital frequency was self-reported by men on a computer-based survey by answering: ‘‘with your current partner, how often do you have sex per month?’’ Coital frequency was defined by examining the monthly coital frequency distribution in the patient population. Coital frequency in the lowest quartile was deemed ‘‘less frequent coitus’’ and in the top three quartiles as ‘‘more frequent coitus.’’
Independent Variables Patient age, years infertile, libido, erectile function, serum T, semen volume, sperm count, and presence of azoospermia were tested as independent variables (Table 1). Duration of infertility was self-reported on a patient questionnaire. It was theorized that the duration of infertility might have a possible effect on coital frequency because couples who are infertile for a long time may lose hope and stop having frequent intercourse. Libido was ‘‘decreased’’ or ‘‘nondecreased’’ based on the answer to question 1 of the Androgen Deficiency in the Aging Male validated questionnaire (4),
which asks ‘‘Do you have a decrease in libido (sex drive).’’ Sexual Health Inventory for Men score was used to measure erectile function. The scale ranges from 0 to >25, and scores below 22 indicate clinically detectable erectile dysfunction (5), with can technically limit coital frequency. Serum T was measured by one of several laboratories at any time during the day. Although T levels are known to fluctuate (6) and collection is suggested during peak early morning levels, this was not practically possible with patients’ availability. However, this wide T fluctuation should only minimally affect our findings because we are concerned with relative differences in T between groups and not absolute values. Serum T supports fertility by contributing to libido and vitality (7). Semen volume, sperm count, and azoospermia were captured from semen analysis. Both semen volume and sperm count were continuous variables. Patients were counseled to remain abstinent for 2 days before semen collection. Semen volume was used as a predictor in our exploratory analysis because, on occasion, low semen volume is a presenting complaint in our clinic by men and we theorize that it may be an indication of T deficiency (the major organs producing semen are T dependent) or potentially decrease their sexual drive by limiting self-confidence. Sperm production is supported by T and sperm count was therefore included as an independent variable. Azoospermia, lack of sperm in ejaculate, was tested in addition to simple sperm count because it represents a common presentation to the infertility clinic and is associated with several unique diagnoses that may also be linked with sexual dysfunction by other mechanisms (i.e., Klinefelter syndrome) (8).
Data Analysis The normality of continuous independent variables was assessed using histogram inspection and Shapiro-Wilk test. Wilcoxon rank sum test was used to test differences in median predictor levels between patients in low versus high coital frequency groups for non-normally distributed variables. For categorical data two-by-two tables were constructed and c2 test was performed.
TABLE 1 Variable dictionary for outcome and independent variables. Independent variable Coital frequency Serum T Age Infertile years Volume Libido SHIM score total Sperm count Azoospermia
Defined
Number of patients with result
Missing values
1 ¼ monthly coital frequency >4 0 ¼ monthly coital frequency %4 Total serum T (nmol/L) Age in years Years infertile Semen volume (mL) 1 ¼ decreased libido 0 ¼ nondecreased libido Total Sexual Health Inventory for Men (SHIM) score Total sperm count ( 106) 1 ¼ azoospermia (zero sperm in ejaculate) 0 ¼ nonazoospermia (presence of some sperm in ejaculate)
1,237
61
411 1,295 1,219 1,264 1,070
887 3 79 34 228
1,298 1,193 1,193
0 105 105
Perlis. Coital frequency and infertility. Fertil Steril 2013.
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FIGURE 1
Self-reported monthly coital frequency for men presenting to male infertility clinic for consultation. Perlis. Coital frequency and infertility. Fertil Steril 2013.
A multivariable logistic regression model was developed using the screening method for variable selection. Variables that were significantly associated with intercourse frequency at a P value cutoff of .25 on bivariate testing were included in the multivariable model. Independent variables were removed from the full multivariable model if the P value was above .25 starting with the model with the highest P value in a stepwise fashion. The omnibus likelihood ratio test was performed to ensure overall model differences. Odds ratio estimates and 95% confidence intervals for each independent variable was explored to assess whether or not there was an independent association at a P value below .05. The four key assumptions of logistic model were assessed: [1] The Hosmer-Lemeshow test of fit was used to assess model fit, [2] overspecification of the model was avoided by not including independent variables measuring similar constructs and by avoiding using variables with few outcomes, [3] influential observations were examined on regression estimates using dfbeta statistic, and [4] outcomes were deemed independent because these couples were not connected beyond seeking therapy in the same clinic.
Model Validation Split sample model validation was performed for this exploratory model by randomly splitting the sample in two (67%/ 33%) (9). A model was derived in the first subsample using the same variable selection technique used with the full model. The model was then tested in the second subsample. C-statistics were compared between both models. If the C-statistic changed by more than 10% the model was not deemed a good fit. VOL. 100 NO. 2 / AUGUST 2013
All P values were two-sided. All statistical tests were performed using SAS v9.2.
RESULTS A total of 1,298 infertile men presented to clinic for consultation and completed at least part of the computer-based survey at the time of initial consultation. The median patient age was 35 years (interquartile range 32–39 years). The median duration of infertility was 2 years before consultation (interquartile range 1–4 years). There was a wide variety of monthly coital frequency reported by infertile men (Fig. 1). The median monthly coital frequency was 7 (interquartile range 5–10), ranging from 0– 40. The lowest 25th percentile reported coital frequency between 0 and 4 times per month. Overall, 7 (0.6%), 33 (2.7%), 60 (4.8%), 72 (5.8%), and 134 (10.8%) men reported having intercourse 0, 1, 2, 3, and 4 times per month, respectively. The results of bivariate and multivariable assessment between independent variables and coital frequency are presented in Table 2. Sperm count was the only independent variable that did not correlate with coital frequency with enough statistical confidence to be included in the multivariable model (P¼ .40). All other variables correlated to coital frequency in the hypothesized direction. Younger age, shorter duration of infertility, better erectile function, higher sperm count, semen volume and serum T, and nondecreased libido were each correlated to more frequent coitus. The omnibus likelihood ratio test was satisfied and key assumptions for the logistic model were met. After variable selection, only four independent variables remained in the multivariable logistic regression model. There were no influential observations. When simultaneously taking into account the influence of age, libido, erectile function, and 513
514
Note: multivariable -2LL omnibus test ¼ 38.8 with 4 degrees of freedom; P< .0001, c-score 0.74. CI ¼ confidence interval; OR ¼ odds ratio; SHIM ¼ Sexual Health Inventory for Men.
38 62 26 74 175 107 77 217 23 77 23 77 173 566 604 295 Decreased libido Nondecreased libido Azoospermia Nonazoospermia
Percent n Percent n
More frequent coitus (R53/mo)
33–41 1.8–5 7–24 8.8–16.0 0–980 1.5–3.5 37 2 22 11 413 2.5 305 300 306 72 294 297 32–38 1–3 22–25 9.7–16.0 8–886 1.8–3.5 35 2 24 13 342 2.5 930 899 931 316 899 907 Age (y) Duration infertility (y) Total SHIM score (/25) Total serum T (nmol/L) Sperm count ( 106) Semen volume (mL)
Perlis. Coital frequency and infertility. Fertil Steril 2013.
n/a .22
.07 0.97–1.89 ref 1.35 < .0001
P value 95% CI OR
Multivariable logistic regression model predicting less frequent coitus
.16 0.84–1.03
DISCUSSION
P value
< .0001 0.85–0.92
semen volume on coital frequency, older patients had had 1.05 times higher odds (per year of age) of less frequent coitus (odds ratio 1.05, 95% confidence interval 1.03–1.08). Patients with better erectile function had 1.12 times higher odds (per point on Sexual Health Inventory for Men scale) of more frequent coitus (odds ratio 1.12, 95% confidence interval 1.09–1.18). Split sample model validation was carried out and demonstrated c-score change of 2.6% and 5% on two different split samples, confirming the validity of the model.
2
Less frequent coitus (<43/mo) Bivariate comparison (c test)
< .0001 1.03–1.08
1.05 n/a 0.89 n/a n/a 0.93 < .0001 .001 < .0001 .13 .4 .01
P value 95% CI OR P value Median Interquartile range n Median Interquartile range n Independent variable
Bivariate comparison (Wilcoxon rank sum) Multivariable logistic regression model predicting less frequent coitus More frequent coitus (R53/mo) Less frequent coitus (<43/mo)
Bivariate assessment and multivariable logistic regression analysis of association between various independent variables and coital frequency.
TABLE 2
ORIGINAL ARTICLE: INFERTILITY
There are a myriad of causes of infertility, and many couples attempt to conceive for many months or years before seeking medical attention (1). Infertile couples report having unsatisfactory sex lives due to scheduling intercourse, sex becoming a mean to an end, invasion of privacy by clinical inquiry, and intercourse reminding patients of their infertility (3). We hypothesize that perhaps this leads to less frequent coitus. To explore this further, we examined coital frequency in infertile couples and explored which variables predicted less frequent coitus. Most infertile couples seeking evaluation are engaging in coitus at least five times per month. The median coital frequency in this cohort of infertile patients was seven. This is similar to that of the general population. In both the National Survey of Sexual Health and Behavior in 2010 (10) and an earlier US survey (11), men and women aged 30–39 years were engaging in sexual intercourse on average seven times per month. Thus, it appears that even couples who have been trying to conceive for 2 years are still engaging in sexual intercourse at a similar rate to their age-matched peers. However, not all infertile couples are having frequent coitus. Approximately 25% of infertile couples are having coitus less than five times per month. When assessing the influence of various clinical parameters independently, increasing age, erectile dysfunction, decreased libido, lower semen volume, and increased duration of infertility were all associated with less frequent coitus. Serum T, overall sperm count, and azoospermia did not have statistically significant associations with coital frequency. However, when taking into account all variables simultaneously, only younger age and good erectile function independently predicted higher frequency coitus. We expected that for couples with infertility the frequency of coitus would be reduced and in particular the frequency would be reduced in those with extended infertility duration. We hypothesized that the stress of the infertility would increase over time and would reduce the sexual interest, functioning, and frequency. However, the frequency of sex in men with infertility was unchanged compared with the general population and the frequency of sex was unrelated to the duration of infertility. Testosterone was also a poor predictor of coital frequency in the multivariable model. Although it is a known predictor of sexual function in older men (7), most men in our study were eugonadal, therefore perhaps changes in T within a normal range were less likely to affect sexual VOL. 100 NO. 2 / AUGUST 2013
Fertility and Sterility® function. Interestingly, post hoc examination confirmed that patients in our cohort with decreased libido did have lower serum T (in nanomoles per liter) than patients with nondecreased libido (mean SD 12.2 5.2 vs. 14.0 5.9; P¼ .01). However, levels for both groups are within normal range, therefore this may not represent a clinically important difference. There are several limitations in this study. The information is from a cross-sectional databases that reflects patients’ experiences at the beginning of their infertility assessment at one clinic. These data were self-reported, sometimes without a partner present to verify the accuracy. In addition, the means of assessing libido relied on self-perception and limited to ‘‘low’’ or ‘‘normal’’ without an option for ‘‘high.’’ We do not report on coital timing to ovulation. Other variables captured in the database (e.g., type of referring physician, woman’s age, clinical characteristics of the female partner) were not tested as independent variables because we were concentrating on the male factors that were most likely to correlate to coital frequency. Data on depression, stress, and anxiety, which could correlate to sexual function (2, 3) and therefore the frequency of sex, were not collected in the database. In the future we will investigate other potential causes for the low frequency of coitus seen in 24% of the infertile couples by including questions on psychological factors like stress, depression, and anxiety. We will also investigate whether or not these couples were still trying to conceive naturally or had already ‘‘given up’’ on natural conception by the time they reached a male infertility clinic. In conclusion, to our knowledge this is the first study of its kind to explore coital frequency and predictors of coital frequency among a cohort of men seeking treatment for infertility. We demonstrated that couples who have been infertile for an extended time are still engaging in relatively frequent coitus. However, there exists a subpopulation that engages in less frequent coitus and these men are generally older and have more erectile dysfunction. Close to 8% of men are hav-
VOL. 100 NO. 2 / AUGUST 2013
ing sex two or less times per month and 24% are engaging in sex four or less times per month. Clinicians investigating men with infertility should be aware that a significant fraction of men with infertility have infrequent coitus and may benefit from targeted interventions. Acknowledgments: The authors thank Charles Victor for statistical assistance and Susan Lau for database management.
REFERENCES 1.
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Boivin J, Bunting L, Collins JA, Nygren KG. International estimates of infertility prevalence and treatment-seeking: potential need and demand for infertility medical care. Hum Reprod 2007;22:1506–12. Monga M, Alexandrescu B, Katz S, Stein M, Ganiats T. Impact of infertility on quality of life, marital adjustment, and sexual function. Urology 2004;63: 126–30. Greil AL, Porter KL, Leitko TA. Sex and intimacy among infertile couples. J Psychol Hum Sex 1989;2:117–38. Morley JE, Charlton E, Patrick P, Kaiser FE, Cadeau P, McCready D, et al. Validation of a screening questionnaire for androgen deficiency in aging males. Metabolism 2000;49:1239–42. Cappelleri J, Rosen R. The Sexual Health Inventory for Men (SHIM): a 5-year review of research and clinical experience. IJIR 2005;17:307–9. Rose RM, Kreuz LE, Holaday JW, Sulak KJ, Johnson CE. Diurnal variation of plasma testosterone and cortisol. J Endocrinol 1972;54:177–8. Isidori AM, Giannetta E, Gianfrilli D, Greco EA, Bonifacio V, Aversa A, et al. Effects of testosterone on sexual function in men: results of a meta-analysis. Clin Endocrinol 2005;63:381–94. Paduch DA, Bolyakov A, Cohen P, Travis A. Reproduction in men with Klinefelter syndrome: the past, the present, and the future. Sem Reprod Med 2009;27:137–48. Austin PC, Tu JV. Automated variable selection methods for logistic regression produced unstable models for predicting acute myocardial infarction mortality. J Clin Epidemiol 2004;57:1138–46. Reece M, Herbenick D, Schick V, Sanders SA, Dodge B, Fortenberry JD. Sexual behaviors, relationships, and perceived health among adult men in the United States: results from a national probability sample. J Sex Med 2010; 7(Suppl 5):291–304. Mosher WD, Chandra A, Jones J. Sexual behavior and selected health measures: men and women 15–44 years of age. Advance data from vital and health statistics, number 362, 2005. Atlanta: CDC; 2002.
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Coital frequency and infertility: which male factors predict less frequent coitus among infertile couples? Nathan Perlis, M.D.,a,b,c Kirk C. Lo, M.D.,a,b,d Ethan D. Grober, M.D.,a,b Leia Spencer, R.N.,b and Keith Jarvi, M.D.a,b,d,e a Department of Surgery, Division of Urology, University of Toronto; b Mount Sinai Hospital; c Institute of Health Policy, Management and Evaluation and d Institute of Medical Science, University of Toronto; and e Samuel Lunenfeld Research Institute, Mount Sinai Hospital, Toronto, Ontario, Canada
Objective: To determine the coital frequency among infertile couples and which factors are associated with less frequent coitus. Design: Cross-sectional study. Setting: Tertiary-level male infertility clinic. Patient(s): A total of 1,298 infertile men. Intervention(s): Administration of computer-based survey, semen analysis, and serum hormone evaluation. Main Outcome Measure(s): Monthly coital frequency. Result(s): A total of 1,298 patients presented to clinic for infertility consultation and completed the computer-based survey. The median male age was 35 years (interquartile range [IQR] 32–39 years) and the median duration of infertility was 2 years (IQR 1–4 years) before consultation. Median monthly coital frequency was seven (IQR 5–10; range 0–40); 24% of couples were having intercourse %4 times per month. Overall, 0.6%, 2.7%, 4.8%, 5.8%, and 10.8% of the men reported having intercourse 0, 1, 2, 3, and 4 times per month, respectively. When simultaneously taking into account the influence of age, libido, erectile function, and semen volume on coital frequency, older patients had 1.05 times higher odds (per year of age) of less frequent coitus (odds ratio 1.05, 95% confidence interval 1.03–1.08). In addition, patients with better erectile function had 1.12 times higher odds (per point on Sexual Health Inventory for Men scale) of more frequent coitus (odds ratio 1.12, 95% confidence interval 1.09–1.18). Conclusion(s): Similar to the general population, most infertile couples report having coitus more than four times per month. Older male age and erectile dysfunction are independent risk factors for less frequent coitus among infertile men, which could have an impact on fertility. Coital frequency should be considered Use your smartphone in infertility assessments. (Fertil SterilÒ 2013;100:511–5. Ó2013 by American Society for to scan this QR code Reproductive Medicine.) and connect to the Key Words: Infertility, infertility assessment, intercourse Discuss: You can discuss this article with its authors and with other ASRM members at http:// fertstertforum.com/perlisn-intercourse-infertility-male-factor/
I
nfertility is caused by male and female factors with both organic and psychological etiologies (1). Prolonged infertility can be a psychosocial stress for the infertile couple leading to poor marital adjustment and decreased quality of life (2). Although some infertile couples report unsatisfactory sex lives (3), to our
knowledge, coital frequency has never been studied in men with infertility. To explore the question of how frequently infertile men were engaging in sex, we reviewed self-reported monthly coital frequency among a population of men presenting for evaluation of male factor infertility at a tertiary
Received November 2, 2012; revised April 8, 2013; accepted April 10, 2013; published online May 10, 2013. N.P. has nothing to disclose. K.C.L. has nothing to disclose. E.D.G. has nothing to disclose. L.S. has nothing to disclose. K.J. has nothing to disclose. Reprint requests: Keith Jarvi, M.D., Murray Koffler Urologic Wellness Centre, Joseph and Wolf Lebovic Building, Mount Sinai Hospital, 6th Floor, 60 Murray Street, Toronto, Ontario, M5T 3L9 Canada (E-mail: [email protected]). Fertility and Sterility® Vol. 100, No. 2, August 2013 0015-0282/$36.00 Copyright ©2013 American Society for Reproductive Medicine, Published by Elsevier Inc. http://dx.doi.org/10.1016/j.fertnstert.2013.04.020 VOL. 100 NO. 2 / AUGUST 2013
discussion forum for this article now.*
* Download a free QR code scanner by searching for “QR scanner” in your smartphone’s app store or app marketplace.
level male infertility clinic. We hypothesized that men presenting to an infertility clinic will be engaging in less frequent coitus than the general population. We were also interested in identifying factors that might predict which men are having less frequent coitus. We hypothesized that increased age, increased duration of infertility, low T and abnormal serum parameters would be associated with low coital frequency.
MATERIALS AND METHODS Data Source We collected and combined data on men from three unique sources at the 511
ORIGINAL ARTICLE: INFERTILITY Mount Sinai Hospital male infertility clinic in Toronto, Ontario, Canada from 2004–2010. Men were referred for investigation of male factor infertility by Reproductive Endocrinology Infertility specialists or family physicians and all of the men had an abnormal semen analysis and/or sperm assessment. Demographic data, referring physicians, treatment history, and risk factors for infertility were selfreported by men presenting for initial infertility assessment on a computer-based survey. These data were captured and linked with serum hormone profiles and semen analysis parameters if blood and semen collection was performed as part of patients’ medical evaluation. Institutional research ethics approval and patient-informed consent were obtained.
Exclusion Criteria Patients were excluded from analysis if survey data or linked serum and hormonal profile information was unavailable.
Outcome Monthly coital frequency was self-reported by men on a computer-based survey by answering: ‘‘with your current partner, how often do you have sex per month?’’ Coital frequency was defined by examining the monthly coital frequency distribution in the patient population. Coital frequency in the lowest quartile was deemed ‘‘less frequent coitus’’ and in the top three quartiles as ‘‘more frequent coitus.’’
Independent Variables Patient age, years infertile, libido, erectile function, serum T, semen volume, sperm count, and presence of azoospermia were tested as independent variables (Table 1). Duration of infertility was self-reported on a patient questionnaire. It was theorized that the duration of infertility might have a possible effect on coital frequency because couples who are infertile for a long time may lose hope and stop having frequent intercourse. Libido was ‘‘decreased’’ or ‘‘nondecreased’’ based on the answer to question 1 of the Androgen Deficiency in the Aging Male validated questionnaire (4),
which asks ‘‘Do you have a decrease in libido (sex drive).’’ Sexual Health Inventory for Men score was used to measure erectile function. The scale ranges from 0 to >25, and scores below 22 indicate clinically detectable erectile dysfunction (5), with can technically limit coital frequency. Serum T was measured by one of several laboratories at any time during the day. Although T levels are known to fluctuate (6) and collection is suggested during peak early morning levels, this was not practically possible with patients’ availability. However, this wide T fluctuation should only minimally affect our findings because we are concerned with relative differences in T between groups and not absolute values. Serum T supports fertility by contributing to libido and vitality (7). Semen volume, sperm count, and azoospermia were captured from semen analysis. Both semen volume and sperm count were continuous variables. Patients were counseled to remain abstinent for 2 days before semen collection. Semen volume was used as a predictor in our exploratory analysis because, on occasion, low semen volume is a presenting complaint in our clinic by men and we theorize that it may be an indication of T deficiency (the major organs producing semen are T dependent) or potentially decrease their sexual drive by limiting self-confidence. Sperm production is supported by T and sperm count was therefore included as an independent variable. Azoospermia, lack of sperm in ejaculate, was tested in addition to simple sperm count because it represents a common presentation to the infertility clinic and is associated with several unique diagnoses that may also be linked with sexual dysfunction by other mechanisms (i.e., Klinefelter syndrome) (8).
Data Analysis The normality of continuous independent variables was assessed using histogram inspection and Shapiro-Wilk test. Wilcoxon rank sum test was used to test differences in median predictor levels between patients in low versus high coital frequency groups for non-normally distributed variables. For categorical data two-by-two tables were constructed and c2 test was performed.
TABLE 1 Variable dictionary for outcome and independent variables. Independent variable Coital frequency Serum T Age Infertile years Volume Libido SHIM score total Sperm count Azoospermia
Defined
Number of patients with result
Missing values
1 ¼ monthly coital frequency >4 0 ¼ monthly coital frequency %4 Total serum T (nmol/L) Age in years Years infertile Semen volume (mL) 1 ¼ decreased libido 0 ¼ nondecreased libido Total Sexual Health Inventory for Men (SHIM) score Total sperm count ( 106) 1 ¼ azoospermia (zero sperm in ejaculate) 0 ¼ nonazoospermia (presence of some sperm in ejaculate)
1,237
61
411 1,295 1,219 1,264 1,070
887 3 79 34 228
1,298 1,193 1,193
0 105 105
Perlis. Coital frequency and infertility. Fertil Steril 2013.
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FIGURE 1
Self-reported monthly coital frequency for men presenting to male infertility clinic for consultation. Perlis. Coital frequency and infertility. Fertil Steril 2013.
A multivariable logistic regression model was developed using the screening method for variable selection. Variables that were significantly associated with intercourse frequency at a P value cutoff of .25 on bivariate testing were included in the multivariable model. Independent variables were removed from the full multivariable model if the P value was above .25 starting with the model with the highest P value in a stepwise fashion. The omnibus likelihood ratio test was performed to ensure overall model differences. Odds ratio estimates and 95% confidence intervals for each independent variable was explored to assess whether or not there was an independent association at a P value below .05. The four key assumptions of logistic model were assessed: [1] The Hosmer-Lemeshow test of fit was used to assess model fit, [2] overspecification of the model was avoided by not including independent variables measuring similar constructs and by avoiding using variables with few outcomes, [3] influential observations were examined on regression estimates using dfbeta statistic, and [4] outcomes were deemed independent because these couples were not connected beyond seeking therapy in the same clinic.
Model Validation Split sample model validation was performed for this exploratory model by randomly splitting the sample in two (67%/ 33%) (9). A model was derived in the first subsample using the same variable selection technique used with the full model. The model was then tested in the second subsample. C-statistics were compared between both models. If the C-statistic changed by more than 10% the model was not deemed a good fit. VOL. 100 NO. 2 / AUGUST 2013
All P values were two-sided. All statistical tests were performed using SAS v9.2.
RESULTS A total of 1,298 infertile men presented to clinic for consultation and completed at least part of the computer-based survey at the time of initial consultation. The median patient age was 35 years (interquartile range 32–39 years). The median duration of infertility was 2 years before consultation (interquartile range 1–4 years). There was a wide variety of monthly coital frequency reported by infertile men (Fig. 1). The median monthly coital frequency was 7 (interquartile range 5–10), ranging from 0– 40. The lowest 25th percentile reported coital frequency between 0 and 4 times per month. Overall, 7 (0.6%), 33 (2.7%), 60 (4.8%), 72 (5.8%), and 134 (10.8%) men reported having intercourse 0, 1, 2, 3, and 4 times per month, respectively. The results of bivariate and multivariable assessment between independent variables and coital frequency are presented in Table 2. Sperm count was the only independent variable that did not correlate with coital frequency with enough statistical confidence to be included in the multivariable model (P¼ .40). All other variables correlated to coital frequency in the hypothesized direction. Younger age, shorter duration of infertility, better erectile function, higher sperm count, semen volume and serum T, and nondecreased libido were each correlated to more frequent coitus. The omnibus likelihood ratio test was satisfied and key assumptions for the logistic model were met. After variable selection, only four independent variables remained in the multivariable logistic regression model. There were no influential observations. When simultaneously taking into account the influence of age, libido, erectile function, and 513
514
Note: multivariable -2LL omnibus test ¼ 38.8 with 4 degrees of freedom; P< .0001, c-score 0.74. CI ¼ confidence interval; OR ¼ odds ratio; SHIM ¼ Sexual Health Inventory for Men.
38 62 26 74 175 107 77 217 23 77 23 77 173 566 604 295 Decreased libido Nondecreased libido Azoospermia Nonazoospermia
Percent n Percent n
More frequent coitus (R53/mo)
33–41 1.8–5 7–24 8.8–16.0 0–980 1.5–3.5 37 2 22 11 413 2.5 305 300 306 72 294 297 32–38 1–3 22–25 9.7–16.0 8–886 1.8–3.5 35 2 24 13 342 2.5 930 899 931 316 899 907 Age (y) Duration infertility (y) Total SHIM score (/25) Total serum T (nmol/L) Sperm count ( 106) Semen volume (mL)
Perlis. Coital frequency and infertility. Fertil Steril 2013.
n/a .22
.07 0.97–1.89 ref 1.35 < .0001
P value 95% CI OR
Multivariable logistic regression model predicting less frequent coitus
.16 0.84–1.03
DISCUSSION
P value
< .0001 0.85–0.92
semen volume on coital frequency, older patients had had 1.05 times higher odds (per year of age) of less frequent coitus (odds ratio 1.05, 95% confidence interval 1.03–1.08). Patients with better erectile function had 1.12 times higher odds (per point on Sexual Health Inventory for Men scale) of more frequent coitus (odds ratio 1.12, 95% confidence interval 1.09–1.18). Split sample model validation was carried out and demonstrated c-score change of 2.6% and 5% on two different split samples, confirming the validity of the model.
2
Less frequent coitus (<43/mo) Bivariate comparison (c test)
< .0001 1.03–1.08
1.05 n/a 0.89 n/a n/a 0.93 < .0001 .001 < .0001 .13 .4 .01
P value 95% CI OR P value Median Interquartile range n Median Interquartile range n Independent variable
Bivariate comparison (Wilcoxon rank sum) Multivariable logistic regression model predicting less frequent coitus More frequent coitus (R53/mo) Less frequent coitus (<43/mo)
Bivariate assessment and multivariable logistic regression analysis of association between various independent variables and coital frequency.
TABLE 2
ORIGINAL ARTICLE: INFERTILITY
There are a myriad of causes of infertility, and many couples attempt to conceive for many months or years before seeking medical attention (1). Infertile couples report having unsatisfactory sex lives due to scheduling intercourse, sex becoming a mean to an end, invasion of privacy by clinical inquiry, and intercourse reminding patients of their infertility (3). We hypothesize that perhaps this leads to less frequent coitus. To explore this further, we examined coital frequency in infertile couples and explored which variables predicted less frequent coitus. Most infertile couples seeking evaluation are engaging in coitus at least five times per month. The median coital frequency in this cohort of infertile patients was seven. This is similar to that of the general population. In both the National Survey of Sexual Health and Behavior in 2010 (10) and an earlier US survey (11), men and women aged 30–39 years were engaging in sexual intercourse on average seven times per month. Thus, it appears that even couples who have been trying to conceive for 2 years are still engaging in sexual intercourse at a similar rate to their age-matched peers. However, not all infertile couples are having frequent coitus. Approximately 25% of infertile couples are having coitus less than five times per month. When assessing the influence of various clinical parameters independently, increasing age, erectile dysfunction, decreased libido, lower semen volume, and increased duration of infertility were all associated with less frequent coitus. Serum T, overall sperm count, and azoospermia did not have statistically significant associations with coital frequency. However, when taking into account all variables simultaneously, only younger age and good erectile function independently predicted higher frequency coitus. We expected that for couples with infertility the frequency of coitus would be reduced and in particular the frequency would be reduced in those with extended infertility duration. We hypothesized that the stress of the infertility would increase over time and would reduce the sexual interest, functioning, and frequency. However, the frequency of sex in men with infertility was unchanged compared with the general population and the frequency of sex was unrelated to the duration of infertility. Testosterone was also a poor predictor of coital frequency in the multivariable model. Although it is a known predictor of sexual function in older men (7), most men in our study were eugonadal, therefore perhaps changes in T within a normal range were less likely to affect sexual VOL. 100 NO. 2 / AUGUST 2013
Fertility and Sterility® function. Interestingly, post hoc examination confirmed that patients in our cohort with decreased libido did have lower serum T (in nanomoles per liter) than patients with nondecreased libido (mean SD 12.2 5.2 vs. 14.0 5.9; P¼ .01). However, levels for both groups are within normal range, therefore this may not represent a clinically important difference. There are several limitations in this study. The information is from a cross-sectional databases that reflects patients’ experiences at the beginning of their infertility assessment at one clinic. These data were self-reported, sometimes without a partner present to verify the accuracy. In addition, the means of assessing libido relied on self-perception and limited to ‘‘low’’ or ‘‘normal’’ without an option for ‘‘high.’’ We do not report on coital timing to ovulation. Other variables captured in the database (e.g., type of referring physician, woman’s age, clinical characteristics of the female partner) were not tested as independent variables because we were concentrating on the male factors that were most likely to correlate to coital frequency. Data on depression, stress, and anxiety, which could correlate to sexual function (2, 3) and therefore the frequency of sex, were not collected in the database. In the future we will investigate other potential causes for the low frequency of coitus seen in 24% of the infertile couples by including questions on psychological factors like stress, depression, and anxiety. We will also investigate whether or not these couples were still trying to conceive naturally or had already ‘‘given up’’ on natural conception by the time they reached a male infertility clinic. In conclusion, to our knowledge this is the first study of its kind to explore coital frequency and predictors of coital frequency among a cohort of men seeking treatment for infertility. We demonstrated that couples who have been infertile for an extended time are still engaging in relatively frequent coitus. However, there exists a subpopulation that engages in less frequent coitus and these men are generally older and have more erectile dysfunction. Close to 8% of men are hav-
VOL. 100 NO. 2 / AUGUST 2013
ing sex two or less times per month and 24% are engaging in sex four or less times per month. Clinicians investigating men with infertility should be aware that a significant fraction of men with infertility have infrequent coitus and may benefit from targeted interventions. Acknowledgments: The authors thank Charles Victor for statistical assistance and Susan Lau for database management.
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