- Email: [email protected]
Gestational weight gain in consecutive pregnancies
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Gestational weight gain in consecutive pregnancies Jeanette R. Chin, MD; Katrina M. Krause, MA; Truls Østbye, MD, PhD; Najmul Chowdhury, MBBS, MPH; Cheryl A. Lovelady, PhD, RD; Geeta K. Swamy, MD OBJECTIVE: The purpose of this study was to examine the association
RESULTS: Compared with women with appropriate GWG in their first
between gestational weight gain (GWG) in a woman’s first and second pregnancies.
pregnancy, women with excessive GWG in their first pregnancy had an odds ratio of 2.6 (95% confidence interval, 2.4 –2.7) for excessive GWG in their second pregnancy. Women with inadequate GWG in their first pregnancy were similarly likely to repeat this category in their subsequent pregnancy.
STUDY DESIGN: We conducted a retrospective observational cohort
study of 27,771 women with their first and second births in North Carolina’s Pregnancy Nutrition Surveillance System database from 19962004. GWG was categorized as inadequate, appropriate, or excessive, according to 2009 Institute of Medicine guidelines. Covariate adjusted polytomous logistic regression was used to test the association between GWG category in the first and second pregnancy.
CONCLUSION: GWG category in a woman’s first pregnancy is a signifi-
cant predictor of GWG category in her subsequent pregnancy. Key words: consecutive pregnancies, gestational weight gain, obesity
Cite this article as: Chin JR, Krause KM, Østbye T, et al. Gestational weight gain in consecutive pregnancies. Am J Obstet Gynecol 2010;203:279.e1-6.
A
pproximately one-third of women aged ⱖ20 years in the United States are obese.1 Obesity is associated with multiple adverse pregnancy outcomes that include miscarriage,2 stillbirth,3,4 congenital anomalies,5 preeclampsia,3,4,6 gestational diabetes mellitus,4,6 fetal macrosomia,4,6 and cesarean section delivery.3,4,6,7 Obese women can decrease their risk for adverse outcomes by gaining less weight during pregnancy.8-10 Because the risks that are associated with inadequate or excessive gestational weight gain (GWG) vary with a woman’s prepregnancy body mass index (BMI), the Institute of Medicine’s (IOM) recommendations for appropriate GWG are conditional on the woman’s prepregnancy BMI category (underweight, normal weight, overweight, or obese).11
Inadequate GWG, particularly among underweight women, is a significant risk factor for preterm birth and low birthweight.8,12,13 Excessive GWG, however, may be an even greater concern, given that approximately 40% and 60% of normalweight and overweight women, respectively, have GWG exceeding IOM recommendations.14 Excessive GWG, even among normal-weight women, is associated with maternal complications such as hypertensive disorders and cesarean delivery and with neonatal complications that include large-for-gestational-age,9,10,15 meconium aspiration, seizures, assisted ventilation, and hypoglycemia.16 Although the immediate obstetric and neonatal consequences of excessive GWG are of great concern, the potential
From the Department of Obstetrics and Gynecology, University of Utah Health Sciences Center, Salt Lake City, UT (Dr Chin); Duke-NUS Graduate Medical School, Singapore (Dr Østbye); and the Departments of Community and Family Medicine (Ms Krause and Dr Østbye) and Obstetrics and Gynecology (Dr Swamy), Duke University Medical Center, Durham; the Nutrition Services Branch, Division of Public Health, North Carolina Department of Health and Human Services, Raleigh (Dr Chowdhury); and the Department of Nutrition, University of North Carolina at Greensboro, Greensboro (Dr Lovelady), NC. Presented as a poster at the 30th Annual Meeting of the Society for Maternal-Fetal Medicine, Chicago, IL, Feb. 1-6, 2010. Received March 1, 2010; revised April 26, 2010; accepted June 17, 2010. Reprints: Jeanette R. Chin, MD, Department of Obstetrics and Gynecology, University of Utah Health Sciences Center, 30 N 1900 E Room 2B200, Salt Lake City, UT 84132. [email protected]. Authorship and contribution to the article is limited to the 6 authors indicated. There was no outside funding or technical assistance with the production of this article. 0002-9378/$36.00 • © 2010 Mosby, Inc. All rights reserved. • doi: 10.1016/j.ajog.2010.06.038
long-term effects on the health of both the mother and her offspring are also being elucidated. Increasing parity, independent of socioeconomic status, is associated with obesity later in life.17 This effect may be compounded by excessive GWG during individual pregnancies, which is a significant risk factor for postpartum weight retention.8,18,19 Studies have also found that excessive GWG, particularly among obese women, is associated with obesity in children.20,21 Most research into predictors of GWG has been cross-sectional in nature, analyzing a single pregnancy for each woman. In these cross-sectional analyses, nulliparity has been identified as a significant risk factor for excessive GWG.14,22 However, few studies have examined GWG in a longitudinal fashion across pregnancies. This type of analysis, which takes into account a woman’s own reproductive history and interpregnancy changes, may be more pertinent when a physician cares for individual patients. Ideally, women with either inadequate or excessive GWG in a first pregnancy, based on IOM guidelines, would not continue this pattern with subsequent pregnancies. Using an ethnically diverse database of linked pregnancies, we sought to determine whether GWG in a woman’s first pregnancy is predictive of GWG in her second pregnancy.
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SMFM Papers M ATERIALS AND M ETHODS Data North Carolina’s Pregnancy Nutrition Surveillance System is compiled by linking data from the North Carolina Special Supplemental Nutrition Program for Women, Infants, and Children (NC WIC) with birth certificates and fetal death certificates. With the exception of the coded NC WIC participant identification number, data from the North Carolina’s Pregnancy Nutrition Surveillance System used for this study were deidentified and obtained through a data use agreement with the North Carolina Department of Health and Human Services. This agreement and the study protocol were approved by the Duke University Institutional Review Board. Study population Women who were enrolled in the NC WIC program for ⬎1 pregnancy between 1996 and 2004 were identified by the coded NC WIC participant identification that was provided in the dataset. Maternal demographic and clinical characteristics, including parity, were collected when women were admitted to the NC WIC program during pregnancy and at the postpartum recertification visit when the mother renews her participation in NC WIC. In an attempt to capture only the first and second live births for each woman (and thus exclude women who may have had an intervening pregnancy during which they were not a participant in the NC WIC program), only women with sequential pregnancies for which parity was recorded as “0” and “1” were included (n ⫽ 47,903). Subjects who had a multifetal gestation during either their first or second pregnancy (n ⫽ 1247) or a gestational age at delivery recorded as ⬍34 weeks for either their first or second pregnancy (n ⫽ 2520) were excluded. There were also 16,189 women with either a missing height, a missing prepregnancy weight for either pregnancy, and/or a missing GWG for either pregnancy who were excluded. To eliminate potential coding errors, only those women with a recorded height between 48-72 inches, recorded prepregnancy weights between 80-600 279.e2
www.AJOG.org lb, and calculated prepregnancy BMI of ⱖ15 kg/m2 were included in the analysis. This resulted in a final analysis sample of 27,771 women.
Measures In 2009, the IOM released updated recommendations for GWG based on prepregnancy BMI: ⬍18.5 kg/m2: 28-40 lbs; 18.5-24.9 kg/m2: 25-35 lbs; 25-29.9 kg/m2: 15-25 lbs; ⱖ30 kg/m2: 11-20 lbs.11 Prepregnancy BMI was calculated with the use of self-reported prepregnancy weight recorded at the NC WIC prenatal visit for each pregnancy and a height measured by WIC office staff. GWG for each pregnancy was obtained from the birth certificate. Based on prepregnancy BMI, subjects were then categorized as having “inadequate” GWG if they gained less than the IOM recommendations, “appropriate” GWG if they gained within the IOM recommendations, and “excessive” GWG if they gained more than the IOM recommendations. We examined several other candidate predictors and potential confounders of the association between GWG in the first and second pregnancies: age at first delivery (⬍21 or ⱖ21 years), race/ethnicity (non-Hispanic white, non-Hispanic black, Hispanic, and other), education (less than high school or high school or higher), smoking during the second pregnancy (yes/no), breastfeeding duration after the first pregnancy (⬍24 or ⱖ24 weeks), and difference in maternal age between the 2 deliveries (⬍2 or ⱖ2 years). Maternal age, race/ethnicity, education, and smoking were variables that were obtained from the birth certificate. The “other” category for race included those women who were coded as ⬎1 racial category. Although variables for smoking in both pregnancies were available, only the variable for smoking in the second pregnancy was used because it was correlated highly with smoking in the first pregnancy (r ⫽ 0.62). The age variable was dichotomized at 21 years to examine how a first pregnancy that occurs in the teenage/adolescent years affects GWG. Breastfeeding duration was recorded at WIC postnatal visits and was
American Journal of Obstetrics & Gynecology SEPTEMBER 2010
defined as “any breastfeeding,” as opposed to “exclusive breastfeeding.”
Statistical analysis GWG category in the first pregnancy served as the primary predictor variable for the primary outcome of GWG category in the second pregnancy. To evaluate for potential colinearity among covariates, correlation coefficients were calculated and demonstrated that none were highly correlated. All variables were modeled with reference cell coding. Excessive and inadequate GWG were compared with appropriate GWG as the reference for both the primary predictor and outcome variables. A polytomous logistic regression model was used to test the association of excessive or inadequate GWG in the first pregnancy with excessive or inadequate GWG in the second pregnancy, while being controlled for the described covariates. To examine whether there were any differences in GWG patterns by BMI, a stratified analysis was done according to the woman’s BMI before her first pregnancy. Separate polytomous logistic regression models that tested the association of GWG category in the first pregnancy with GWG category in the second pregnancy, controlling for the described covariates, were calculated for women in each of 4 prepregnancy BMI categories: underweight, normal weight, overweight, and obese. The polytomous models are summarized by odds ratios with corresponding 95% CIs. All statistical tests used a 2-sided ␣ of .05. Analysis was performed with SAS software (version 9.2; SAS Institute Inc, Cary, NC).
R ESULTS Characteristics of the analysis sample (n ⫽ 27,771) are presented in Table 1. Approximately one-third of women had their first live birth at an age ⬍21 years, and approximately 20% of the women had their second live birth within 2 years after their first. The study sample consisted of a nearly equal proportion of non-Hispanic white and non-Hispanic black women (47% and 40%, respectively) and a small proportion of Hispanic women (9%). Most women breastfed for ⬍24 weeks after their first
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TABLE 1
Characteristics of study sample (n ⴝ 27,771) Variable
n (%)
Age at 1st pregnancy
.....................................................................................................................................................................................................................................
⬍21 y
8943 (32.2)
ⱖ21 y
18,828 (67.8)
..................................................................................................................................................................................................................................... ..............................................................................................................................................................................................................................................
Age difference between pregnancies
.....................................................................................................................................................................................................................................
⬍2 y
5393 (19.4)
ⱖ2 y
22,378 (80.6)
..................................................................................................................................................................................................................................... .............................................................................................................................................................................................................................................. a
Education at 1st pregnancy
.....................................................................................................................................................................................................................................
⬍High school
13,598 (49.0)
ⱖHigh school
14,145 (51.0)
..................................................................................................................................................................................................................................... ..............................................................................................................................................................................................................................................
Race/ethnicity
.....................................................................................................................................................................................................................................
Non-Hispanic white
13,014 (46.9)
Non-Hispanic black
11,222 (40.4)
..................................................................................................................................................................................................................................... .....................................................................................................................................................................................................................................
Hispanic
2354 (8.5)
Other
1181 (4.3)
..................................................................................................................................................................................................................................... .............................................................................................................................................................................................................................................. a
Breastfeeding after 1st pregnancy
.....................................................................................................................................................................................................................................
⬍24 wk
18,397 (74.5)
ⱖ24 wk
6285 (25.5)
..................................................................................................................................................................................................................................... .............................................................................................................................................................................................................................................. a
Smoking in 2nd pregnancy
.....................................................................................................................................................................................................................................
No
21,493 (77.5)
.....................................................................................................................................................................................................................................
Yes
6228 (22.5)
.............................................................................................................................................................................................................................................. 2
Prepregnancy body mass index, kg/m
..................................................................................................................................................................................................................................... b
1st pregnancy
23.6 (20.6–28.4)
2nd pregnancy
25.9 (21.9–31.6)
..................................................................................................................................................................................................................................... b .............................................................................................................................................................................................................................................. c
Body mass index category before 1st pregnancy
.....................................................................................................................................................................................................................................
Underweight
3430 (12.4)
.....................................................................................................................................................................................................................................
Normal weight
14,796 (53.3)
.....................................................................................................................................................................................................................................
Overweight
3241 (11.7)
Obese
6304 (22.7)
..................................................................................................................................................................................................................................... .............................................................................................................................................................................................................................................. c
Body mass index category before 2nd pregnancy
.....................................................................................................................................................................................................................................
Underweight
2376 (8.6)
.....................................................................................................................................................................................................................................
Normal weight
11,835 (42.6)
.....................................................................................................................................................................................................................................
Overweight
3897 (14.0)
Obese
9663 (34.8)
..................................................................................................................................................................................................................................... .............................................................................................................................................................................................................................................. d
Gestational weight gain
..................................................................................................................................................................................................................................... d
1st pregnancy, lb
33.2 ⫾ 14.5
2nd pregnancy, lb
28.0 ⫾ 13.9
..................................................................................................................................................................................................................................... d .............................................................................................................................................................................................................................................. a
Frequencies do not add to total sample size of 27,771 because of missing data; b Data are given as median (interquartile range); c Body mass index categories: underweight, ⬍18.5 kg/m2; normal weight, 18.5-24.9 kg/m2; overweight, 25-29.9 kg/m2; obese, ⱖ30 kg/m2; d Data are given as mean ⫾ SD.
Chin. Gestational weight gain. Am J Obstet Gynecol 2010
pregnancy and did not smoke during their second pregnancy. The median first prepregnancy BMI was 23.6 kg/m2 (interquartile range, 20.6 –28.4 kg/m2), and the median second prepregnancy BMI was 25.9 kg/m2 (interquartile range, 21.9 –31.6 kg/m2). The most frequent IOM GWG category for both the first and second pregnancies was excessive GWG (49% and 41%, respectively). In the first pregnancy, 67% of obese women had excessive GWG, compared with 43% of normal-weight women. In the second pregnancy, 55% of obese women had excessive GWG, compared with 31% of normal-weight women. A relatively large proportion of women were in the same GWG category for both of their pregnancies (Table 2). For example, 57% of the women who had excessive GWG in their first pregnancy had excessive GWG in their second pregnancy; 49% of the women who had inadequate GWG in their first pregnancy had inadequate GWG in their second pregnancy. In a multivariable linear regression model (data not shown) that was adjusted for BMI before the first pregnancy and for age, race, education, age difference between pregnancies, and breastfeeding duration, excessive GWG in the first pregnancy was a significant risk factor for an increased BMI before the second pregnancy. Results of the final polytomous model are presented in Table 3. After covariate adjustment, women who had excessive GWG in their first pregnancy had an odds ratio of 2.6 (95% confidence interval, 2.4 –2.7) for excessive GWG in their second pregnancy, compared with women with appropriate GWG in their first pregnancy. Similarly, women who had inadequate GWG in their first pregnancy had an odds ratio of 2.1 (95% confidence interval, 1.9 –2.3) for inadequate GWG in their second pregnancy, compared with women with appropriate GWG in their first pregnancy. GWG category in the first pregnancy was the strongest predictor of GWG category in the second pregnancy. Although some of the other covariates had statistically significant odds ratios for their association with GWG category in the second pregnancy, they were generally near 1.0 with
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TABLE 2
Gestational weight gain categories among linked pregnancies, n (%)a First pregnancy gestational weight gain
Second pregnancy gestational weight gain Inadequate
Appropriate
Inadequate
2693 (49.4)
1813 (33.3)
Excessive 944 (17.3)
Total 5450
Appropriate
2468 (28.6)
3492 (40.4)
2678 (31.0)
8638
Excessive
1945 (14.2)
3975 (29.1)
7763 (56.7)
13,683
Column total
7106
9280
.............................................................................................................................................................................................................................................. .............................................................................................................................................................................................................................................. ..............................................................................................................................................................................................................................................
11,385
.............................................................................................................................................................................................................................................. a
Gestational weight gain categories were defined in accordance with 2009 Institute of Medicine guidelines.
Chin. Gestational weight gain. Am J Obstet Gynecol 2010.
narrow CIs (which reflected the large sample size) and thus of relatively limited clinical significance. Table 4 shows the results of the analysis that was stratified by BMI before the first pregnancy. Regardless of whether the woman was underweight, normal weight, overweight, or obese before her first pregnancy, she was at similarly increased odds of repeating the same GWG in her second pregnancy, compared with having appropriate weight gain in her second pregnancy.
C OMMENT Multiple studies have identified risk factors for excessive GWG, including nulliparity, obesity, increased maternal age, and increased time in the United States for Hispanic women.22,23 In this study, we were able to analyze GWG patterns in 2 consecutive pregnancies among a large and ethnically diverse number of women and found that GWG category in a previous pregnancy is an important predictor of GWG category in a subsequent pregnancy. Overall, a lower proportion
TABLE 3
Final polytomous regression model: adjusted association of GWG categories in 1st and 2nd pregnanciesa GWG category in 2nd pregnancyb,c Predictor
Reference
GWG category in 1st pregnancyc
Appropriate GWG
Inadequate
Excessive
.....................................................................................................................................................................................................................................
Inadequate
2.1 (1.9–2.3)
0.7 (0.6–0.7)
0.7 (0.6–0.8)
2.6 (2.4–2.7)
.....................................................................................................................................................................................................................................
Excessive
..............................................................................................................................................................................................................................................
Race/ethnicity
Non-Hispanic white
.....................................................................................................................................................................................................................................
Non-Hispanic black
1.2 (1.1–1.3)
1.1 (1.0–1.2)
Hispanic
1.1 (1.0–1.2)
0.9 (0.8–1.0)
..................................................................................................................................................................................................................................... .....................................................................................................................................................................................................................................
1.3 (1.1–1.6)
0.9 (0.8–1.1)
ⱖ21 years old at 1st delivery
Other race
⬍21 y
1.0 (0.9–1.1)
1.1 (1.1–1.2)
ⱖHigh school education at 1st delivery
⬍High school
0.9 (0.9–1.0)
1.0 (0.9–1.0)
ⱖ2 years between deliveries
⬍2 y
0.9 (0.8–0.9)
1.2 (1.1–1.3)
Nonsmoker in 2nd pregnancy
Smoker
0.9 (0.9–1.0)
1.2 (1.1–1.3)
ⱖ24 weeks breastfeeding after 1st pregnancy
⬍24 wk
0.9 (0.8–1.0)
1.0 (0.9–1.1)
.............................................................................................................................................................................................................................................. .............................................................................................................................................................................................................................................. .............................................................................................................................................................................................................................................. .............................................................................................................................................................................................................................................. ..............................................................................................................................................................................................................................................
..............................................................................................................................................................................................................................................
GWG, gestational weight gain. a
Final model includes 24,614 subjects with nonmissing data for all variables; b Data are given as odds ratio (95% confidence interval); c GWG categories were defined in accordance with 2009 Institute of Medicine guidelines.
Chin. Gestational weight gain. Am J Obstet Gynecol 2010.
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American Journal of Obstetrics & Gynecology SEPTEMBER 2010
of women had excessive GWG in their second pregnancy, compared with their first; however, it is troubling that excessive GWG was the most frequent category of weight gain for both pregnancies. Although less GWG in the second pregnancy might seem positive, this is likely counteracted to some extent by a greater likelihood of being obese (and thus at risk for obesity-related adverse pregnancy outcomes) before the second pregnancy. Indeed, Villamor and Cnattingius,24 in an analysis of 151,025 linked pregnancies in Sweden, found that women whose BMI increased by ⱖ3 units during an average of 2 years between pregnancies were at greater risk of hypertensive disorders, gestational diabetes mellitus, cesarean delivery, fetal death, and large-for-gestational age infants in their second pregnancies than women whose BMI changed minimally. Our findings suggest that a large proportion of women compound their risks by being obese and continuing to have excessive GWG. In our final adjusted polytomous model, women who had excessive or inadequate GWG in their first pregnancy were at significantly greater odds of having GWG in that same category for the second pregnancy. The results of this study indicate that some obese women, for example, appear to repeat excessive GWG across pregnancies while other women repeat inadequate weight gain. This raises the question of whether the determinants of GWG are more complex than simply the balance of caloric intake and physical activity. The underlying reason for repeating the same GWG pattern is more likely multifactorial, involving sociocultural (mediated through factors not captured in this study), metabolic, and genetic issues. Adipose tissue is now understood to be not simply an energy reservoir but also a metabolically active organ that influences many aspects of reproduction.25 Adipokines (or molecular products of adipose tissue such as leptin) may play important roles in the determination of GWG.26 Further research into the molecular basis of obesity and weight gain in pregnancy, including an evaluation of the impact of genetic differences, is needed.
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TABLE 4
Adjusted association of GWG categories in 1st and 2nd pregnancies, stratified by body mass index before the 1st pregnancya,b Body mass index and GWG category in 1st pregnancyd Underweight (body mass index, ⱕ18.4 kg/m2)
GWG category in 2nd pregnancyc,d Reference
Inadequate
Excessive
Appropriate
.....................................................................................................................................................................................................................................
Inadequate
2.8 (2.3–3.4)
0.6 (0.5–0.8)
Excessive
0.7 (0.6–0.9)
2.8 (2.3–3.5)
..................................................................................................................................................................................................................................... ..............................................................................................................................................................................................................................................
Normal weight (body mass index, 18.5-24.9 kg/m2 )
Appropriate
.....................................................................................................................................................................................................................................
Inadequate
2.0 (1.8–2.2)
0.6 (0.6–0.7)
0.7 (0.6–0.7)
2.1 (2.0–2.3)
.....................................................................................................................................................................................................................................
Excessive
..............................................................................................................................................................................................................................................
Overweight (body mass index, 25.0-29.9 kg/m2 )
Appropriate
.....................................................................................................................................................................................................................................
Inadequate
2.1 (1.5–3.0)
0.7 (0.5–1.0)
Excessive
0.7 (0.5–0.9)
2.5 (2.1–3.1)
..................................................................................................................................................................................................................................... .............................................................................................................................................................................................................................................. 2
Obese (body mass index, ⱖ30 kg/m )
Appropriate
.....................................................................................................................................................................................................................................
Inadequate
1.8 (1.4–2.2)
0.8 (0.6–1.0)
Excessive
0.7 (0.6–0.8)
2.2 (1.9–2.6)
..................................................................................................................................................................................................................................... ..............................................................................................................................................................................................................................................
GWG, gestational weight gain. a
Covariates in stratified models are maternal age (at 1st pregnancy), age difference between pregnancies, race/ethnicity, smoking (in 2nd pregnancy), and breastfeeding duration (after the 1st pregnancy); b Stratified models include the following number of subjects with no missing data for all variables: underweight, 3037 women; normal weight, 13,072 women; overweight, 2861 women; obese, 5644 women; c Data are given as odds ratio (95% confidence interval); d GWG categories were defined in accordance with 2009 Institute of Medicine guidelines.
Chin. Gestational weight gain. Am J Obstet Gynecol 2010.
The postpartum period has been the target of interventions that have been designed to promote weight loss and limit postpartum weight retention with variable results.27-30 It may be that antepartum interventions that are aimed at preventing excessive GWG might be more effective because of the frequency with which pregnant women encounter the healthcare system and the lack of the demands of caring for a newborn. Several recently published studies have evaluated GWG interventions. Wolff et al31 found that obese pregnant women who received dietary counseling did have lower GWG than those without counseling. In a randomized controlled trial of dietary and lifestyle counseling in pregnancy, Asbee et al32 found that those women who had counseling had significantly less GWG than those who did not, but there were no differences with regards to adherence to IOM guidelines. Kinnunen et al33 found that dietary and
physical activity counseling during pregnancy was not effective at decreasing the proportion of primiparous women who exceeded weight gain recommendations. We used a unique approach to link consecutive pregnancies within a relatively large database of ethnically diverse women. Drawing from a WIC database, our study population was inherently of lower socioeconomic status, which affects the generalizability of our findings to more socioeconomically advantaged pregnant women. However, this remains a particularly important group in which to study GWG, given the higher rates of obesity (and less access to care) among socioeconomically disadvantaged women.34 Another important limitation of studies that use population databases is the data accuracy. In this study, prepregnancy weight was self-reported. Women tend to underreport their weight by 3-4 pounds, more so if they are overweight or obese.35,36 As a result, it is
possible that some of the assigned GWG categories are inaccurate. The GWG variable was obtained from birth certificates either as a self-reported measure or calculated from self-reported prepregnancy weight and measured gestational weight. A recent study, however, found that GWG on the North Carolina birth certificate was highly correlated with the GWG that was recorded as part of a prospective cohort study.37 Although North Carolina WIC data are recorded by trained staff, some coding errors may occur. However, given the relatively large sample size, such errors are unlikely to have significantly affected the results. Finally, weight and height variables were not available for many women, which raises the possibility that unmeasured variables might affect the relationship between the primary predictor and outcome. Such factors are inherent to retrospective studies and must be considered in the context of the use of a large, established population-based cohorts, such as North Carolina’s Pregnancy Nutrition Surveillance System. GWG is important not only because of its effect on immediate maternal and neonatal outcomes but also because of the potential long-term health consequences for women and their children. Our study demonstrates that GWG is often consistent across pregnancies. As a result, women who are at risk of inadequate or excessive GWG ideally would be identified before conception. However, among socioeconomically disadvantaged women with pregnancies that frequently are unplanned and who may have limited access to care between pregnancies, it is more likely that those women who are at risk for inappropriate GWG would be identified early in the prenatal period. This early prenatal period may represent an important “window of opportunity” for nutrition and lifestyle counseling. Ultimately, to find the most effective ways in which to help pregnant women achieve appropriate weight gain, future studies are needed that move past demographic and clinical associations to examine the metabolic and genetic contributions to GWG. f
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SMFM Papers ACKNOWLEDGMENT We thank Alice Lenihan, RD, MPH, LDN, Branch Head of Nutrition Services Branch, Raleigh, NC, Department of Health and Human Services, for facilitating access to the data that were used in this report.
REFERENCES 1. Ogden CL, Carroll MD, Curtin LR, McDowell MA, Tabak CJ, Flegal KM. Prevalence of overweight and obesity in the United States, 19992004. JAMA 2006;295:1549-55. 2. Metwally M, Ong KJ, Ledger WL, Li TC. Does high body mass index increase the risk of miscarriage after spontaneous and assisted conception? A meta-analysis of the evidence. Fertil Steril 2008;90:714-26. 3. Cedergren MI. Maternal morbid obesity and the risk of adverse pregnancy outcome. Obstet Gynecol 2004;103:219-24. 4. Sebire NJ, Jolly M, Harris JP, et al. Maternal obesity and pregnancy outcome: a study of 287,213 pregnancies in London. Int J Obes Relat Metab Disord 2001;25:1175-82. 5. Stothard KJ, Tennant PW, Bell R, Rankin J. Maternal overweight and obesity and the risk of congenital anomalies: a systematic review and meta-analysis. JAMA 2009;301:636-50. 6. Weiss JL, Malone FD, Emig D, et al. Obesity, obstetric complications and cesarean delivery rate: a population-based screening study. Am J Obstet Gynecol 2004;190:1091-7. 7. Crane SS, Wojtowycz MA, Dye TD, Aubry RH, Artal R. Association between pre-pregnancy obesity and the risk of cesarean delivery. Obstet Gynecol 1997;89:213-6. 8. Nohr EA, Vaeth M, Baker JL, Sorensen T, Olsen J, Rasmussen KM. Combined associations of prepregnancy body mass index and gestational weight gain with the outcome of pregnancy. Am J Clin Nutr 2008;87:1750-9. 9. Crane JM, White J, Murphy P, Burrage L, Hutchens D. The effect of gestational weight gain by body mass index on maternal and neonatal outcomes. J Obstet Gynaecol Can 2009; 31:28-35. 10. Cedergren M. Effects of gestational weight gain and body mass index on obstetric outcome in Sweden. Int J Gynaecol Obstet 2006; 93:269-74. 11. Institute of Medicine. Weight gain during pregnancy: reexamining the guidelines. Washington (DC): National Academies Press; 2009.
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www.AJOG.org 12. Dietz PM, Callaghan WM, Cogswell ME, Morrow B, Ferre C, Schieve LA. Combined effects of prepregnancy body mass index and weight gain during pregnancy on the risk of preterm delivery. Epidemiology 2006;17:170-7. 13. Ehrenberg HM, Dierker L, Milluzzi C, Mercer BM. Low maternal weight, failure to thrive in pregnancy, and adverse pregnancy outcomes. Am J Obstet Gynecol 2003;189:1726-30. 14. Chu SY, Callaghan WM, Bish CL, D’Angelo D. Gestational weight gain by body mass index among US women delivering live births, 20042005: fueling future obesity. Am J Obstet Gynecol 2009;200:271.e1-7. 15. DeVader SR, Neeley HL, Myles TD, Leet TL. Evaluation of gestational weight gain guidelines for women with normal prepregnancy body mass index. Obstet Gynecol 2007;110:745-51. 16. Stotland NE, Cheng YW, Hopkins LM, Caughey AB. Gestational weight gain and adverse neonatal outcome among term infants. Obstet Gynecol 2006;108:635-43. 17. Bastian LA, West NA, Corcoran C, Munger RG. Number of children and the risk of obesity in older women. Prev Med 2005;40:99-104. 18. Amorim AR, Rossner S, Neovius M, Lourenco PM, Linne Y. Does excess pregnancy weight gain constitute a major risk for increasing long-term BMI? Obesity (Silver Spring) 2007; 15:1278-86. 19. Gunderson EP, Abrams B, Selvin S. The relative importance of gestational gain and maternal characteristics associated with the risk of becoming overweight after pregnancy. Int J Obes Relat Metab Disord 2000;24:1660-8. 20. Oken E, Rifas-Shiman SL, Field AE, Frazier AL, Gillman MW. Maternal gestational weight gain and offspring weight in adolescence. Obstet Gynecol 2008;112:999-1006. 21. Olson CM, Strawderman MS, Dennison BA. Maternal weight gain during pregnancy and child weight at age 3 years. Matern Child Health J 2009;13:839-46. 22. Caulfield LE, Witter FR, Stoltzfus RJ. Determinants of gestational weight gain outside the recommended ranges among black and white women. Obstet Gynecol 1996;87:760-6. 23. Chasan-Taber L, Schmidt MD, Pekow P, Sternfeld B, Solomon CG, Markenson G. Predictors of excessive and inadequate gestational weight gain in Hispanic women. Obesity (Silver Spring) 2008;16:1657-66. 24. Villamor E, Cnattingius S. Interpregnancy weight change and risk of adverse pregnancy
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outcomes: a population-based study. Lancet 2006;368:1164-70. 25. Sagawa N, Yura S, Itoh H, et al. Role of leptin in pregnancy: a review. Placenta 2002; 23(suppl A):S80-6. 26. Stein TP, Scholl TO, Schluter MD, Schroeder CM. Plasma leptin influences gestational weight gain and postpartum weight retention. Am J Clin Nutr 1998;68:1236-40. 27. Ostbye T, Krause KM, Lovelady CA, et al. Active mothers postpartum: a randomized controlled weight-loss intervention trial. Am J Prev Med 2009;37:173-80. 28. O’Toole ML, Sawicki MA, Artal R. Structured diet and physical activity prevent postpartum weight retention. J Womens Health (Larchmt) 2003;12:991-8. 29. Kinnunen TI, Pasanen M, Aittasalo M, Fogelholm M, Weiderpass E, Luoto R. Reducing postpartum weight retention: a pilot trial in primary health care. Nutr J 2007;6:21. 30. Leermakers EA, Anglin K, Wing RR. Reducing postpartum weight retention through a correspondence intervention. Int J Obes Relat Metab Disord 1998;22:1103-9. 31. Wolff S, Legarth J, Vangsgaard K, Toubro S, Astrup A. A randomized trial of the effects of dietary counseling on gestational weight gain and glucose metabolism in obese pregnant women. Int J Obes (Lond) 2008;32:495-501. 32. Asbee SM, Jenkins TR, Butler JR, White J, Elliot M, Rutledge A. Preventing excessive weight gain during pregnancy through dietary and lifestyle counseling: a randomized controlled trial. Obstet Gynecol 2009;113:305-12. 33. Kinnunen TI, Pasanen M, Aittasalo M, et al. Preventing excessive weight gain during pregnancy: a controlled trial in primary health care. Eur J Clin Nutr 2007;61:884-91. 34. Chu SY, Kim SY, Bish CL. Prepregnancy obesity prevalence in the United States, 20042005. Matern Child Health J 2009;13:614-20. 35. Brunner Huber LR. Validity of self-reported height and weight in women of reproductive age. Matern Child Health J 2007;11:137-44. 36. Merrill RM, Richardson JS. Validity of selfreported height, weight, and body mass index: findings from the National Health and Nutrition Examination Survey, 2001-2006. Prev Chronic Dis 2009;6:A121. 37. Vinikoor LC, Messer LC, Laraia BA, Kaufman JS. Reliability of variables on the North Carolina birth certificate: a comparison with directly queried values from a cohort study. Paediatr Perinat Epidemiol 2010;24:102-12.
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Gestational weight gain in consecutive pregnancies Jeanette R. Chin, MD; Katrina M. Krause, MA; Truls Østbye, MD, PhD; Najmul Chowdhury, MBBS, MPH; Cheryl A. Lovelady, PhD, RD; Geeta K. Swamy, MD OBJECTIVE: The purpose of this study was to examine the association
RESULTS: Compared with women with appropriate GWG in their first
between gestational weight gain (GWG) in a woman’s first and second pregnancies.
pregnancy, women with excessive GWG in their first pregnancy had an odds ratio of 2.6 (95% confidence interval, 2.4 –2.7) for excessive GWG in their second pregnancy. Women with inadequate GWG in their first pregnancy were similarly likely to repeat this category in their subsequent pregnancy.
STUDY DESIGN: We conducted a retrospective observational cohort
study of 27,771 women with their first and second births in North Carolina’s Pregnancy Nutrition Surveillance System database from 19962004. GWG was categorized as inadequate, appropriate, or excessive, according to 2009 Institute of Medicine guidelines. Covariate adjusted polytomous logistic regression was used to test the association between GWG category in the first and second pregnancy.
CONCLUSION: GWG category in a woman’s first pregnancy is a signifi-
cant predictor of GWG category in her subsequent pregnancy. Key words: consecutive pregnancies, gestational weight gain, obesity
Cite this article as: Chin JR, Krause KM, Østbye T, et al. Gestational weight gain in consecutive pregnancies. Am J Obstet Gynecol 2010;203:279.e1-6.
A
pproximately one-third of women aged ⱖ20 years in the United States are obese.1 Obesity is associated with multiple adverse pregnancy outcomes that include miscarriage,2 stillbirth,3,4 congenital anomalies,5 preeclampsia,3,4,6 gestational diabetes mellitus,4,6 fetal macrosomia,4,6 and cesarean section delivery.3,4,6,7 Obese women can decrease their risk for adverse outcomes by gaining less weight during pregnancy.8-10 Because the risks that are associated with inadequate or excessive gestational weight gain (GWG) vary with a woman’s prepregnancy body mass index (BMI), the Institute of Medicine’s (IOM) recommendations for appropriate GWG are conditional on the woman’s prepregnancy BMI category (underweight, normal weight, overweight, or obese).11
Inadequate GWG, particularly among underweight women, is a significant risk factor for preterm birth and low birthweight.8,12,13 Excessive GWG, however, may be an even greater concern, given that approximately 40% and 60% of normalweight and overweight women, respectively, have GWG exceeding IOM recommendations.14 Excessive GWG, even among normal-weight women, is associated with maternal complications such as hypertensive disorders and cesarean delivery and with neonatal complications that include large-for-gestational-age,9,10,15 meconium aspiration, seizures, assisted ventilation, and hypoglycemia.16 Although the immediate obstetric and neonatal consequences of excessive GWG are of great concern, the potential
From the Department of Obstetrics and Gynecology, University of Utah Health Sciences Center, Salt Lake City, UT (Dr Chin); Duke-NUS Graduate Medical School, Singapore (Dr Østbye); and the Departments of Community and Family Medicine (Ms Krause and Dr Østbye) and Obstetrics and Gynecology (Dr Swamy), Duke University Medical Center, Durham; the Nutrition Services Branch, Division of Public Health, North Carolina Department of Health and Human Services, Raleigh (Dr Chowdhury); and the Department of Nutrition, University of North Carolina at Greensboro, Greensboro (Dr Lovelady), NC. Presented as a poster at the 30th Annual Meeting of the Society for Maternal-Fetal Medicine, Chicago, IL, Feb. 1-6, 2010. Received March 1, 2010; revised April 26, 2010; accepted June 17, 2010. Reprints: Jeanette R. Chin, MD, Department of Obstetrics and Gynecology, University of Utah Health Sciences Center, 30 N 1900 E Room 2B200, Salt Lake City, UT 84132. [email protected]. Authorship and contribution to the article is limited to the 6 authors indicated. There was no outside funding or technical assistance with the production of this article. 0002-9378/$36.00 • © 2010 Mosby, Inc. All rights reserved. • doi: 10.1016/j.ajog.2010.06.038
long-term effects on the health of both the mother and her offspring are also being elucidated. Increasing parity, independent of socioeconomic status, is associated with obesity later in life.17 This effect may be compounded by excessive GWG during individual pregnancies, which is a significant risk factor for postpartum weight retention.8,18,19 Studies have also found that excessive GWG, particularly among obese women, is associated with obesity in children.20,21 Most research into predictors of GWG has been cross-sectional in nature, analyzing a single pregnancy for each woman. In these cross-sectional analyses, nulliparity has been identified as a significant risk factor for excessive GWG.14,22 However, few studies have examined GWG in a longitudinal fashion across pregnancies. This type of analysis, which takes into account a woman’s own reproductive history and interpregnancy changes, may be more pertinent when a physician cares for individual patients. Ideally, women with either inadequate or excessive GWG in a first pregnancy, based on IOM guidelines, would not continue this pattern with subsequent pregnancies. Using an ethnically diverse database of linked pregnancies, we sought to determine whether GWG in a woman’s first pregnancy is predictive of GWG in her second pregnancy.
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SMFM Papers M ATERIALS AND M ETHODS Data North Carolina’s Pregnancy Nutrition Surveillance System is compiled by linking data from the North Carolina Special Supplemental Nutrition Program for Women, Infants, and Children (NC WIC) with birth certificates and fetal death certificates. With the exception of the coded NC WIC participant identification number, data from the North Carolina’s Pregnancy Nutrition Surveillance System used for this study were deidentified and obtained through a data use agreement with the North Carolina Department of Health and Human Services. This agreement and the study protocol were approved by the Duke University Institutional Review Board. Study population Women who were enrolled in the NC WIC program for ⬎1 pregnancy between 1996 and 2004 were identified by the coded NC WIC participant identification that was provided in the dataset. Maternal demographic and clinical characteristics, including parity, were collected when women were admitted to the NC WIC program during pregnancy and at the postpartum recertification visit when the mother renews her participation in NC WIC. In an attempt to capture only the first and second live births for each woman (and thus exclude women who may have had an intervening pregnancy during which they were not a participant in the NC WIC program), only women with sequential pregnancies for which parity was recorded as “0” and “1” were included (n ⫽ 47,903). Subjects who had a multifetal gestation during either their first or second pregnancy (n ⫽ 1247) or a gestational age at delivery recorded as ⬍34 weeks for either their first or second pregnancy (n ⫽ 2520) were excluded. There were also 16,189 women with either a missing height, a missing prepregnancy weight for either pregnancy, and/or a missing GWG for either pregnancy who were excluded. To eliminate potential coding errors, only those women with a recorded height between 48-72 inches, recorded prepregnancy weights between 80-600 279.e2
www.AJOG.org lb, and calculated prepregnancy BMI of ⱖ15 kg/m2 were included in the analysis. This resulted in a final analysis sample of 27,771 women.
Measures In 2009, the IOM released updated recommendations for GWG based on prepregnancy BMI: ⬍18.5 kg/m2: 28-40 lbs; 18.5-24.9 kg/m2: 25-35 lbs; 25-29.9 kg/m2: 15-25 lbs; ⱖ30 kg/m2: 11-20 lbs.11 Prepregnancy BMI was calculated with the use of self-reported prepregnancy weight recorded at the NC WIC prenatal visit for each pregnancy and a height measured by WIC office staff. GWG for each pregnancy was obtained from the birth certificate. Based on prepregnancy BMI, subjects were then categorized as having “inadequate” GWG if they gained less than the IOM recommendations, “appropriate” GWG if they gained within the IOM recommendations, and “excessive” GWG if they gained more than the IOM recommendations. We examined several other candidate predictors and potential confounders of the association between GWG in the first and second pregnancies: age at first delivery (⬍21 or ⱖ21 years), race/ethnicity (non-Hispanic white, non-Hispanic black, Hispanic, and other), education (less than high school or high school or higher), smoking during the second pregnancy (yes/no), breastfeeding duration after the first pregnancy (⬍24 or ⱖ24 weeks), and difference in maternal age between the 2 deliveries (⬍2 or ⱖ2 years). Maternal age, race/ethnicity, education, and smoking were variables that were obtained from the birth certificate. The “other” category for race included those women who were coded as ⬎1 racial category. Although variables for smoking in both pregnancies were available, only the variable for smoking in the second pregnancy was used because it was correlated highly with smoking in the first pregnancy (r ⫽ 0.62). The age variable was dichotomized at 21 years to examine how a first pregnancy that occurs in the teenage/adolescent years affects GWG. Breastfeeding duration was recorded at WIC postnatal visits and was
American Journal of Obstetrics & Gynecology SEPTEMBER 2010
defined as “any breastfeeding,” as opposed to “exclusive breastfeeding.”
Statistical analysis GWG category in the first pregnancy served as the primary predictor variable for the primary outcome of GWG category in the second pregnancy. To evaluate for potential colinearity among covariates, correlation coefficients were calculated and demonstrated that none were highly correlated. All variables were modeled with reference cell coding. Excessive and inadequate GWG were compared with appropriate GWG as the reference for both the primary predictor and outcome variables. A polytomous logistic regression model was used to test the association of excessive or inadequate GWG in the first pregnancy with excessive or inadequate GWG in the second pregnancy, while being controlled for the described covariates. To examine whether there were any differences in GWG patterns by BMI, a stratified analysis was done according to the woman’s BMI before her first pregnancy. Separate polytomous logistic regression models that tested the association of GWG category in the first pregnancy with GWG category in the second pregnancy, controlling for the described covariates, were calculated for women in each of 4 prepregnancy BMI categories: underweight, normal weight, overweight, and obese. The polytomous models are summarized by odds ratios with corresponding 95% CIs. All statistical tests used a 2-sided ␣ of .05. Analysis was performed with SAS software (version 9.2; SAS Institute Inc, Cary, NC).
R ESULTS Characteristics of the analysis sample (n ⫽ 27,771) are presented in Table 1. Approximately one-third of women had their first live birth at an age ⬍21 years, and approximately 20% of the women had their second live birth within 2 years after their first. The study sample consisted of a nearly equal proportion of non-Hispanic white and non-Hispanic black women (47% and 40%, respectively) and a small proportion of Hispanic women (9%). Most women breastfed for ⬍24 weeks after their first
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TABLE 1
Characteristics of study sample (n ⴝ 27,771) Variable
n (%)
Age at 1st pregnancy
.....................................................................................................................................................................................................................................
⬍21 y
8943 (32.2)
ⱖ21 y
18,828 (67.8)
..................................................................................................................................................................................................................................... ..............................................................................................................................................................................................................................................
Age difference between pregnancies
.....................................................................................................................................................................................................................................
⬍2 y
5393 (19.4)
ⱖ2 y
22,378 (80.6)
..................................................................................................................................................................................................................................... .............................................................................................................................................................................................................................................. a
Education at 1st pregnancy
.....................................................................................................................................................................................................................................
⬍High school
13,598 (49.0)
ⱖHigh school
14,145 (51.0)
..................................................................................................................................................................................................................................... ..............................................................................................................................................................................................................................................
Race/ethnicity
.....................................................................................................................................................................................................................................
Non-Hispanic white
13,014 (46.9)
Non-Hispanic black
11,222 (40.4)
..................................................................................................................................................................................................................................... .....................................................................................................................................................................................................................................
Hispanic
2354 (8.5)
Other
1181 (4.3)
..................................................................................................................................................................................................................................... .............................................................................................................................................................................................................................................. a
Breastfeeding after 1st pregnancy
.....................................................................................................................................................................................................................................
⬍24 wk
18,397 (74.5)
ⱖ24 wk
6285 (25.5)
..................................................................................................................................................................................................................................... .............................................................................................................................................................................................................................................. a
Smoking in 2nd pregnancy
.....................................................................................................................................................................................................................................
No
21,493 (77.5)
.....................................................................................................................................................................................................................................
Yes
6228 (22.5)
.............................................................................................................................................................................................................................................. 2
Prepregnancy body mass index, kg/m
..................................................................................................................................................................................................................................... b
1st pregnancy
23.6 (20.6–28.4)
2nd pregnancy
25.9 (21.9–31.6)
..................................................................................................................................................................................................................................... b .............................................................................................................................................................................................................................................. c
Body mass index category before 1st pregnancy
.....................................................................................................................................................................................................................................
Underweight
3430 (12.4)
.....................................................................................................................................................................................................................................
Normal weight
14,796 (53.3)
.....................................................................................................................................................................................................................................
Overweight
3241 (11.7)
Obese
6304 (22.7)
..................................................................................................................................................................................................................................... .............................................................................................................................................................................................................................................. c
Body mass index category before 2nd pregnancy
.....................................................................................................................................................................................................................................
Underweight
2376 (8.6)
.....................................................................................................................................................................................................................................
Normal weight
11,835 (42.6)
.....................................................................................................................................................................................................................................
Overweight
3897 (14.0)
Obese
9663 (34.8)
..................................................................................................................................................................................................................................... .............................................................................................................................................................................................................................................. d
Gestational weight gain
..................................................................................................................................................................................................................................... d
1st pregnancy, lb
33.2 ⫾ 14.5
2nd pregnancy, lb
28.0 ⫾ 13.9
..................................................................................................................................................................................................................................... d .............................................................................................................................................................................................................................................. a
Frequencies do not add to total sample size of 27,771 because of missing data; b Data are given as median (interquartile range); c Body mass index categories: underweight, ⬍18.5 kg/m2; normal weight, 18.5-24.9 kg/m2; overweight, 25-29.9 kg/m2; obese, ⱖ30 kg/m2; d Data are given as mean ⫾ SD.
Chin. Gestational weight gain. Am J Obstet Gynecol 2010
pregnancy and did not smoke during their second pregnancy. The median first prepregnancy BMI was 23.6 kg/m2 (interquartile range, 20.6 –28.4 kg/m2), and the median second prepregnancy BMI was 25.9 kg/m2 (interquartile range, 21.9 –31.6 kg/m2). The most frequent IOM GWG category for both the first and second pregnancies was excessive GWG (49% and 41%, respectively). In the first pregnancy, 67% of obese women had excessive GWG, compared with 43% of normal-weight women. In the second pregnancy, 55% of obese women had excessive GWG, compared with 31% of normal-weight women. A relatively large proportion of women were in the same GWG category for both of their pregnancies (Table 2). For example, 57% of the women who had excessive GWG in their first pregnancy had excessive GWG in their second pregnancy; 49% of the women who had inadequate GWG in their first pregnancy had inadequate GWG in their second pregnancy. In a multivariable linear regression model (data not shown) that was adjusted for BMI before the first pregnancy and for age, race, education, age difference between pregnancies, and breastfeeding duration, excessive GWG in the first pregnancy was a significant risk factor for an increased BMI before the second pregnancy. Results of the final polytomous model are presented in Table 3. After covariate adjustment, women who had excessive GWG in their first pregnancy had an odds ratio of 2.6 (95% confidence interval, 2.4 –2.7) for excessive GWG in their second pregnancy, compared with women with appropriate GWG in their first pregnancy. Similarly, women who had inadequate GWG in their first pregnancy had an odds ratio of 2.1 (95% confidence interval, 1.9 –2.3) for inadequate GWG in their second pregnancy, compared with women with appropriate GWG in their first pregnancy. GWG category in the first pregnancy was the strongest predictor of GWG category in the second pregnancy. Although some of the other covariates had statistically significant odds ratios for their association with GWG category in the second pregnancy, they were generally near 1.0 with
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TABLE 2
Gestational weight gain categories among linked pregnancies, n (%)a First pregnancy gestational weight gain
Second pregnancy gestational weight gain Inadequate
Appropriate
Inadequate
2693 (49.4)
1813 (33.3)
Excessive 944 (17.3)
Total 5450
Appropriate
2468 (28.6)
3492 (40.4)
2678 (31.0)
8638
Excessive
1945 (14.2)
3975 (29.1)
7763 (56.7)
13,683
Column total
7106
9280
.............................................................................................................................................................................................................................................. .............................................................................................................................................................................................................................................. ..............................................................................................................................................................................................................................................
11,385
.............................................................................................................................................................................................................................................. a
Gestational weight gain categories were defined in accordance with 2009 Institute of Medicine guidelines.
Chin. Gestational weight gain. Am J Obstet Gynecol 2010.
narrow CIs (which reflected the large sample size) and thus of relatively limited clinical significance. Table 4 shows the results of the analysis that was stratified by BMI before the first pregnancy. Regardless of whether the woman was underweight, normal weight, overweight, or obese before her first pregnancy, she was at similarly increased odds of repeating the same GWG in her second pregnancy, compared with having appropriate weight gain in her second pregnancy.
C OMMENT Multiple studies have identified risk factors for excessive GWG, including nulliparity, obesity, increased maternal age, and increased time in the United States for Hispanic women.22,23 In this study, we were able to analyze GWG patterns in 2 consecutive pregnancies among a large and ethnically diverse number of women and found that GWG category in a previous pregnancy is an important predictor of GWG category in a subsequent pregnancy. Overall, a lower proportion
TABLE 3
Final polytomous regression model: adjusted association of GWG categories in 1st and 2nd pregnanciesa GWG category in 2nd pregnancyb,c Predictor
Reference
GWG category in 1st pregnancyc
Appropriate GWG
Inadequate
Excessive
.....................................................................................................................................................................................................................................
Inadequate
2.1 (1.9–2.3)
0.7 (0.6–0.7)
0.7 (0.6–0.8)
2.6 (2.4–2.7)
.....................................................................................................................................................................................................................................
Excessive
..............................................................................................................................................................................................................................................
Race/ethnicity
Non-Hispanic white
.....................................................................................................................................................................................................................................
Non-Hispanic black
1.2 (1.1–1.3)
1.1 (1.0–1.2)
Hispanic
1.1 (1.0–1.2)
0.9 (0.8–1.0)
..................................................................................................................................................................................................................................... .....................................................................................................................................................................................................................................
1.3 (1.1–1.6)
0.9 (0.8–1.1)
ⱖ21 years old at 1st delivery
Other race
⬍21 y
1.0 (0.9–1.1)
1.1 (1.1–1.2)
ⱖHigh school education at 1st delivery
⬍High school
0.9 (0.9–1.0)
1.0 (0.9–1.0)
ⱖ2 years between deliveries
⬍2 y
0.9 (0.8–0.9)
1.2 (1.1–1.3)
Nonsmoker in 2nd pregnancy
Smoker
0.9 (0.9–1.0)
1.2 (1.1–1.3)
ⱖ24 weeks breastfeeding after 1st pregnancy
⬍24 wk
0.9 (0.8–1.0)
1.0 (0.9–1.1)
.............................................................................................................................................................................................................................................. .............................................................................................................................................................................................................................................. .............................................................................................................................................................................................................................................. .............................................................................................................................................................................................................................................. ..............................................................................................................................................................................................................................................
..............................................................................................................................................................................................................................................
GWG, gestational weight gain. a
Final model includes 24,614 subjects with nonmissing data for all variables; b Data are given as odds ratio (95% confidence interval); c GWG categories were defined in accordance with 2009 Institute of Medicine guidelines.
Chin. Gestational weight gain. Am J Obstet Gynecol 2010.
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American Journal of Obstetrics & Gynecology SEPTEMBER 2010
of women had excessive GWG in their second pregnancy, compared with their first; however, it is troubling that excessive GWG was the most frequent category of weight gain for both pregnancies. Although less GWG in the second pregnancy might seem positive, this is likely counteracted to some extent by a greater likelihood of being obese (and thus at risk for obesity-related adverse pregnancy outcomes) before the second pregnancy. Indeed, Villamor and Cnattingius,24 in an analysis of 151,025 linked pregnancies in Sweden, found that women whose BMI increased by ⱖ3 units during an average of 2 years between pregnancies were at greater risk of hypertensive disorders, gestational diabetes mellitus, cesarean delivery, fetal death, and large-for-gestational age infants in their second pregnancies than women whose BMI changed minimally. Our findings suggest that a large proportion of women compound their risks by being obese and continuing to have excessive GWG. In our final adjusted polytomous model, women who had excessive or inadequate GWG in their first pregnancy were at significantly greater odds of having GWG in that same category for the second pregnancy. The results of this study indicate that some obese women, for example, appear to repeat excessive GWG across pregnancies while other women repeat inadequate weight gain. This raises the question of whether the determinants of GWG are more complex than simply the balance of caloric intake and physical activity. The underlying reason for repeating the same GWG pattern is more likely multifactorial, involving sociocultural (mediated through factors not captured in this study), metabolic, and genetic issues. Adipose tissue is now understood to be not simply an energy reservoir but also a metabolically active organ that influences many aspects of reproduction.25 Adipokines (or molecular products of adipose tissue such as leptin) may play important roles in the determination of GWG.26 Further research into the molecular basis of obesity and weight gain in pregnancy, including an evaluation of the impact of genetic differences, is needed.
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TABLE 4
Adjusted association of GWG categories in 1st and 2nd pregnancies, stratified by body mass index before the 1st pregnancya,b Body mass index and GWG category in 1st pregnancyd Underweight (body mass index, ⱕ18.4 kg/m2)
GWG category in 2nd pregnancyc,d Reference
Inadequate
Excessive
Appropriate
.....................................................................................................................................................................................................................................
Inadequate
2.8 (2.3–3.4)
0.6 (0.5–0.8)
Excessive
0.7 (0.6–0.9)
2.8 (2.3–3.5)
..................................................................................................................................................................................................................................... ..............................................................................................................................................................................................................................................
Normal weight (body mass index, 18.5-24.9 kg/m2 )
Appropriate
.....................................................................................................................................................................................................................................
Inadequate
2.0 (1.8–2.2)
0.6 (0.6–0.7)
0.7 (0.6–0.7)
2.1 (2.0–2.3)
.....................................................................................................................................................................................................................................
Excessive
..............................................................................................................................................................................................................................................
Overweight (body mass index, 25.0-29.9 kg/m2 )
Appropriate
.....................................................................................................................................................................................................................................
Inadequate
2.1 (1.5–3.0)
0.7 (0.5–1.0)
Excessive
0.7 (0.5–0.9)
2.5 (2.1–3.1)
..................................................................................................................................................................................................................................... .............................................................................................................................................................................................................................................. 2
Obese (body mass index, ⱖ30 kg/m )
Appropriate
.....................................................................................................................................................................................................................................
Inadequate
1.8 (1.4–2.2)
0.8 (0.6–1.0)
Excessive
0.7 (0.6–0.8)
2.2 (1.9–2.6)
..................................................................................................................................................................................................................................... ..............................................................................................................................................................................................................................................
GWG, gestational weight gain. a
Covariates in stratified models are maternal age (at 1st pregnancy), age difference between pregnancies, race/ethnicity, smoking (in 2nd pregnancy), and breastfeeding duration (after the 1st pregnancy); b Stratified models include the following number of subjects with no missing data for all variables: underweight, 3037 women; normal weight, 13,072 women; overweight, 2861 women; obese, 5644 women; c Data are given as odds ratio (95% confidence interval); d GWG categories were defined in accordance with 2009 Institute of Medicine guidelines.
Chin. Gestational weight gain. Am J Obstet Gynecol 2010.
The postpartum period has been the target of interventions that have been designed to promote weight loss and limit postpartum weight retention with variable results.27-30 It may be that antepartum interventions that are aimed at preventing excessive GWG might be more effective because of the frequency with which pregnant women encounter the healthcare system and the lack of the demands of caring for a newborn. Several recently published studies have evaluated GWG interventions. Wolff et al31 found that obese pregnant women who received dietary counseling did have lower GWG than those without counseling. In a randomized controlled trial of dietary and lifestyle counseling in pregnancy, Asbee et al32 found that those women who had counseling had significantly less GWG than those who did not, but there were no differences with regards to adherence to IOM guidelines. Kinnunen et al33 found that dietary and
physical activity counseling during pregnancy was not effective at decreasing the proportion of primiparous women who exceeded weight gain recommendations. We used a unique approach to link consecutive pregnancies within a relatively large database of ethnically diverse women. Drawing from a WIC database, our study population was inherently of lower socioeconomic status, which affects the generalizability of our findings to more socioeconomically advantaged pregnant women. However, this remains a particularly important group in which to study GWG, given the higher rates of obesity (and less access to care) among socioeconomically disadvantaged women.34 Another important limitation of studies that use population databases is the data accuracy. In this study, prepregnancy weight was self-reported. Women tend to underreport their weight by 3-4 pounds, more so if they are overweight or obese.35,36 As a result, it is
possible that some of the assigned GWG categories are inaccurate. The GWG variable was obtained from birth certificates either as a self-reported measure or calculated from self-reported prepregnancy weight and measured gestational weight. A recent study, however, found that GWG on the North Carolina birth certificate was highly correlated with the GWG that was recorded as part of a prospective cohort study.37 Although North Carolina WIC data are recorded by trained staff, some coding errors may occur. However, given the relatively large sample size, such errors are unlikely to have significantly affected the results. Finally, weight and height variables were not available for many women, which raises the possibility that unmeasured variables might affect the relationship between the primary predictor and outcome. Such factors are inherent to retrospective studies and must be considered in the context of the use of a large, established population-based cohorts, such as North Carolina’s Pregnancy Nutrition Surveillance System. GWG is important not only because of its effect on immediate maternal and neonatal outcomes but also because of the potential long-term health consequences for women and their children. Our study demonstrates that GWG is often consistent across pregnancies. As a result, women who are at risk of inadequate or excessive GWG ideally would be identified before conception. However, among socioeconomically disadvantaged women with pregnancies that frequently are unplanned and who may have limited access to care between pregnancies, it is more likely that those women who are at risk for inappropriate GWG would be identified early in the prenatal period. This early prenatal period may represent an important “window of opportunity” for nutrition and lifestyle counseling. Ultimately, to find the most effective ways in which to help pregnant women achieve appropriate weight gain, future studies are needed that move past demographic and clinical associations to examine the metabolic and genetic contributions to GWG. f
SEPTEMBER 2010 American Journal of Obstetrics & Gynecology
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SMFM Papers ACKNOWLEDGMENT We thank Alice Lenihan, RD, MPH, LDN, Branch Head of Nutrition Services Branch, Raleigh, NC, Department of Health and Human Services, for facilitating access to the data that were used in this report.
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