Objective: To estimate the impact of excess pregnancy weight gain and failure to lose weight by 6 months postpartum on excess weight 8-10 years later.

Methods: Seven hundred ninety-five women were observed through pregnancy and 6 months postpartum to examine factors that affect weight loss. Weight was recorded 10 years later through a medical record review to examine the impact of retained weight on long-term obesity. Overall weight change at last follow-up and body mass index (BMI) were examined by pregnancy weight gain appropriateness according to the Institute of Medicine guidelines for weight gain during pregnancy.

Results: Of the original cohort, 540 women had a documented weight beyond 5 years (mean = 8.5 years). The average weight gain from prepregnancy to follow-up was 6.3 kg. There was no difference in weight gain by prepregnancy BMI. Women who gained less than the recommended amount during their pregnancy were 4.1 kg heavier at follow-up, those gaining the recommended amount were 6.5 kg heavier, and those gaining more than recommended were 8.4 kg heavier (P = .01). Women who lost all pregnancy weight by 6 months postpartum were 2.4 kg heavier at follow-up than women with retained weight, who weighed 8.3 kg more at follow-up (P = .01). Women who breast-fed and women who participated in aerobic exercise also had significantly lower weight gains.

Conclusion: Excess weight gain and failure to lose weight after pregnancy are important and identifiable predictors of long-term obesity. Breast-feeding and exercise may be beneficial to control long-term weight.

^aGundersen Lutheran Medical Center, La Crosse, Wisconsin, USA

The Gundersen Lutheran Medical Foundation supported this work.

(Obstet Gynecol 2002:100:245-252. © 2002 by The American College of Obstetricians and Gynecologists.)

National data indicate that, in 1998, 18% of women in the United States were considered obese (body mass index [BMI] of 30 or more).¹ Adults of childbearing age have seen between a 50% and 70% increase in the rate of obesity since 1991.² The known risks of morbidity and mortality associated with being overweight, including breast cancer, heart disease, and diabetes, make factors associated with weight gain in women an important public health concern.^3-6

According to national prevalence estimates from the Second National Health and Nutrition Examination Survey, overweight is most likely to be present in middle-aged and elderly women, and the development of weight problems would most likely occur some time before middle age.⁷ These data show that the incidence of major weight gain is highest among adults aged 25-34 years; women were twice as likely as men to have a major weight gain. More striking, however, is that younger women who were already overweight at baseline had the highest incidence of major weight gain.⁷

Pregnancy is a time in most women's lives where significant weight is gained. In 1990, the Institute of Medicine published new guidelines relating to weight gain during pregnancy.⁸ The development of these recommendations was based on the Institute's findings that the effect of weight gain on fetal size diminishes as the mother's prepregnant body size increases. A major objective of these recommendations is to optimize fetal birth weight; little is known about how prenatal weight gain affects the long-term health of the mother. Recognizing that larger weight gains may be associated with subsequent obesity, the Institute of Medicine has identified the impact of gestational weight gain on maternal pregnancy outcome and maternal obesity as an area where further research is needed.⁸

What impact does excess weight gain during pregnancy have on long-term changes in weight? Are there certain women for whom excess pregnancy weight gain will be the beginning of a long-term weight problem? There have been a number of studies that have looked at prenatal weight gain and postpartum weight retention.^9-15 The limited length of follow-up and cross-sectional nature of some of these studies do not make it possible to determine if postpartum maternal weight represents pregnancy weight retention or a regain of weight after an initial loss. Our initial study¹⁶ and the results we present here of follow-up 10 years after the study pregnancy allow for a better understanding of the characteristics related to weight change after pregnancy and the long-term implications of weight retention.

Materials and Methods

The original study was conducted at the Gundersen Clinic, Ltd. and Lutheran Hospital in La Crosse, Wisconsin, from April 1, 1989 to March 30, 1990 and had full institutional review board approval. Methods and results from this study are described in detail elsewhere and are summarized briefly below.¹⁶ A convenience sample of women with uncomplicated pregnancies were observed from their first prenatal visit through their pregnancy until 6 months postpartum. Ninety-seven percent of the participants were white and middle class. Because of the inaccuracies of self-reported weight, prepregnancy weights were not obtained and we used weight recorded at the first prenatal visit as the starting weight. A majority of women presented for prenatal care during the first trimester when weight gain is fairly minimal; the average gestational age at the first prenatal visit was 10.4 weeks. Additional maternal weights were recorded at 20 weeks' gestation, at delivery, and then at discharge, 2, 4, 6, 8, 12, and 24 weeks (6 months) postpartum. Prenatal weight measurements occurred on standard clinic scales in the obstetrics or family practice departments, whereas postpartum weights were measured in the pediatrics or family practice departments. Women also completed surveys at each follow-up interval indicating their status on certain behaviors such as breast-feeding, use of tobacco or alcohol, sexual activity, return to work, and frequency of exercise. All items were assessed based on status over the previous 2-week interval (4 and 12 weeks for later follow-up). In 1999, we conducted a medical record review to obtain study participants' last known weight measured at a clinic visit. Parity at follow-up was also recorded.

The major dependent variables for this study were weight gain from first prenatal visit to last known follow-up (weight change) and BMI at last known follow-up (follow-up BMI). Body mass index is determined as weight in kilograms, divided by a squared measure of height in meters. Of major interest was how prepregnancy weight (first prenatal weight), as defined by prepregnancy BMI (pre-BMI); appropriateness of weight gain during pregnancy (weight gain categories); and pregnancy weight gain not lost by 6 months postpartum (retained weight categories) were related to weight change and follow-up BMI. Weight gain categories were based on the Institute of Medicine recommendations that are determined by prepregnancy BMI. For women considered underweight (pre-BMI < 19.8) weight gain should be between 12.5 and 18.0 kg, for normal weight women (pre-BMI = 19.8-26.0) weight gain should be between 11.5 and 16.0 kg, for overweight women (pre-BMI = 26.1-29.9) weight gain should be between 7.0 and 11.5 kg, and for obese women (pre-BMI > 29.9) weight gain should be greater than 6.0 kg. Since little information is available about the effects of weight gain on birth weight in obese women, the Institute of Medicine did not specify an upper weight gain limit for obese women. Weight gain categories were then defined as gaining above the recommended amount, gaining the recommended amount, or gaining below the recommended amount. Retained weight categories were defined as having lost all pregnancy weight gained or having any retained weight at 6 months postpartum.

All analysis was conducted using SAS statistical software 6 (SAS Institute Inc., Cary, NC). Univariate analysis consisted of analysis of variance models and ² statistics. Post hoc comparisons were conducted for significant findings using Tukey's honestly significant difference analysis to minimize the inflation of type I error due to making multiple comparisons.¹⁷ Variables that were significant in the univariate analysis were also entered into a multiple linear regression model to develop the best model to predict weight change and follow-up BMI. We were also interested in examining how predictors of weight change and BMI at this follow-up may have differed from a shorter follow-up, by 6 months postpartum. We thus ran companion models predicting 6-month retained weight (short-term weight change) and BMI at 6 months postpartum (postpartum BMI). Because of the high and expected correlation between prepregnancy, postpartum, and follow-up BMIs, prepregnancy BMI was not included in any of the multivariable models predicting BMI.

Results

Of the 795 women included in the previous study, 540 (68%) continued their care at our clinic and had a weight available 5-10 years after their study pregnancy. Because we were mainly interested in the long-term changes in weight, women without weight measures beyond 5 years were excluded from the analysis. The women that did not continue care at our clinic were about 1 year younger, started prenatal care about 2 weeks later, were slightly more likely to be obese, but were more likely to have lost their pregnancy weight by 6 months postpartum compared to those women that continued care at our clinic (Table 1). The average length of follow-up for women continuing care at our facility was 8.5 years.

The average gain in weight from prepregnancy to 6 months postpartum was 1.7 kg (Table 2). At long-term follow-up, the average weight gain was 6.3 kg. Short- and long-term weight gains did not differ for prepregnancy BMI, parity, or age. Short-term weight gains did not differ for duration of breast-feeding or self-reported participation in aerobic exercise. However, at long-term follow-up, average weight gains did differ for both of these. At long-term follow-up, women who did not breast-feed or only breast-fed for 2 weeks or less had the largest weight gain from before pregnancy. Women who breast-fed beyond 12 weeks had the smallest weight gain (post hoc comparison P values < .05). Women who reported they were participating in aerobic exercise in the postpartum period had significantly less weight gain at long-term follow-up than those not reporting this. Weight gains did not differ significantly for self-report of other physical activity, such as regular walking, running, biking, or swimming, at either follow-up. Although women who smoked reported significantly less weight gain at 6 months postpartum, the difference was not significant at long-term follow-up.

The most significant predictors of weight change at long-term follow-up were weight gain during pregnancy and weight retention at 6 months postpartum. Those women who gained more than the recommended amount during pregnancy had significantly higher weight gain at long-term follow-up than women who gained the recommended amount or less than that during pregnancy. Women who were able to lose the weight they gained during pregnancy were only 2.4 kg heavier at long-term follow-up than women who had retained weight by 6 months postpartum; they were on average 8.3 kg heavier. No other variables gathered at pregnancy or during the postpartum period were significantly related to weight change at 6-month or long-term follow-up. The multivariable model including weight gain categories, retained weight, breast-feeding duration, and aerobic exercise was statistically significant and predicted 14% of the variation in long-term weight change (R² = 0.139) (Table 3).

At 6 months postpartum, the average BMI was 25.6, and at long-term follow-up, the average was 27.3 (Table 4). Age, parity, and smoking status at prepregnancy were not related to BMI at either follow-up period. Similar to the analysis for predictors of weight change, breast-feeding duration was not related to BMI at 6 months postpartum, but was related to BMI at long-term follow-up. Women who continued to breast-feed at 12 weeks postpartum or beyond had a significantly lower BMI at long-term follow-up than those women who did not breast-feed, or did so for less than 12 weeks. Also similar to results for weight gain, women who reported participating in aerobic exercise were likely to have a lower follow-up BMI than women who did not report this.

Follow-up BMIs differed significantly by weight gain appropriateness. Women who gained less than the recommended amount had a significantly lower BMI at long-term follow-up than women who gained the recommended amount or more. Average follow-up BMIs for women who gained the recommended amount did not differ significantly from those of women who gained more than the recommended amount (Tukey's post hoc analysis P > .05.) The univariate analysis also showed that women who lost their pregnancy weight gain were more likely to have a lower follow-up BMI than women who had retained weight at 6 months postpartum. No other variables gathered during pregnancy or the postpartum period significantly predicted postpartum or follow-up BMI. The final multivariable model contained weight gain appropriateness, retained weight, breast-feeding duration, and self-reported participation in aerobic exercise. The final model was statistically significant and predicted 8% of the variance in follow-up BMI (R² = 0.082) (Table 3).

Discussion

The results from this study show that excess weight gain during pregnancy and failure to lose weight after pregnancy are important predictors of long-term weight changes and higher BMI many years after a pregnancy. In addition, our study revealed that although breast-feeding may not have an immediate short-term weight loss benefit for the mother, at long-term follow-up, women who breast-fed their child for at least 3 months had a significantly lower weight gain over an average of 8.5 years. This study also showed that although women might not see immediate weight loss benefits from aerobic exercise, there are significant long-term benefits in terms of weight gain and BMI. We are unsure of the exact mechanism for these two findings. Other forms of exercise (walking, running, biking, and swimming) were also self-reported; however, these activities were not found to be significant. We could postulate that 6 months was too soon to see major changes in the fat stores for women who were breast-feeding or exercising and that it took longer to see the benefits of these two activities. This finding could also suggest other lifestyle choices or characteristics of women who choose to breast-feed beyond 3 months or report being engaged in aerobic exercise. Long-term weight change and BMI were not related to mother's occupation at the time of pregnancy.

The research studies regarding the short-term weight loss benefits from breast-feeding and exercise have been mixed. Some studies have found a weak but negative association between lactation and weight retention.^13,18 Ohlin and Rossnen¹³ found that a higher lactation score, as measured by a summary score of duration and intensity, was related to a higher mean weight loss between 2.5 and 6 months postpartum, but mean weight loss did not differ from those of the groups with the lower scores by 12 months postpartum. Another, small study of 49 women found a positive association between lactation and weight retention.¹⁹ Women who breast-fed longer than 8 weeks gained more body mass over the postpartum period than nonpregnant women. Gunderson and Abrams,²⁰ in a comprehensive review of gestational weight gain and body weight changes after pregnancy, suggest that better measures of lactation duration and intensity are needed to help sort out the association of lactation and weight changes.

In the Ohlin and Rossner study,¹³ there was a weak association between increased leisure time physical activity and lower weight retention at 1 year postpartum. Another study found a significantly lower retained weight at 6 weeks postpartum among women who engaged in physical activity.²¹ However, Boardley et al²² found no relationship between physical activity and weight retention.

Unlike the Second National Health and Nutrition Examination Survey results showing that women who were already overweight at baseline had the highest weight gain,⁷ our study showed that weight gains did not differ by baseline BMI, but differed by appropriateness of pregnancy weight gain and women's ability to lose the excess weight.

Only 68% of the original cohort in our study had long-term follow-up data. This may have affected the overall results of this study; however, we believe the effect was minimal. Our institution is a tertiary hospital and clinic that serves a large rural area including 28 small regional clinics. Many of the women in these rural areas came to our institution for prenatal care, but continued receiving their primary care from their own local physician. (This would explain the slightly higher gestational age at first prenatal visit for those not observed beyond 5 years.) Weight measures by their local physician were not available for our study. The findings that there was no difference in weight gained during pregnancy between those who continued care and those who did not, and that those lost to follow-up had less retained weight, would suggest that if these women were included in the long-term follow-up the results would be even stronger in the same direction that we found.

Although prepregnancy weights were not available, we feel that using the first prenatal weight was a good approximation for this weight. Because most of the first prenatal visits were less than ten weeks' gestation, weight gain should have been minimal. Although there was not close quality control on the accuracy of the weights obtained within the clinic setting, the scales in the clinic are routinely calibrated and should have been as accurate in 1989 as they were in 1999 or any time in between.

The Institute of Medicine does not place an upper limit on the appropriate weight gain for women with BMI greater than 29.9. We looked at the potential impact of this on our study. We saw the same relationship for short- and long-term weight change among the obese women at first prenatal visit. At long-term follow-up, obese women gaining more than 25 lb during pregnancy were 7.5 kg heavier than prepregnancy, women who gained the recommended amount were 5.4 kg heavier, and those who gained less than the recommended amount were at the same weight as prepregnancy. Thus, if we put an upper limit on the weight gain category for obese women, the effect on the entire study would be to magnify the effects we report. Future research should study the impact of weight gain on fetal health and birth outcomes among obese women to determine a healthy weight gain.

We feel our study is unique. No study to date has looked at the effect of weight gain and weight loss postpartum on long-term weight changes a decade after pregnancy on a cohort of women. Ohlin and Rossner,¹³ who performed another cohort study like our initial study,¹⁶ reported an average retention of 1.5 kg at 1 year postpartum in 1423 Swedish women. Several other longitudinal studies^11,12,14,15 have examined postpartum weight loss, but none of these have observed the women beyond 1 year.

Keppel and Taffel⁹ examined differences in women's pregnancy and postpartum weights 10-18 months after delivery. Similar to our study, they found that weight retention after delivery increased as weight gain increased. The median retained weight increase in their study changed from 0.9 lb for those who gained less than recommended, 1.6 lb for those who gained the recommended, and 4.9 lb for those who gained more than recommended. They also found that the association between weight gain and retained weight was not substantially altered when controlling for parity, breast-feeding, or employment status. Parker and Abrams¹⁰ examined data from the 1988 National Maternal and Infant Health Survey of women within the normal BMI category. They concluded that among white mothers, socioeconomic status, education, family income, marital status, and prenatal weight gain were significantly associated with retained weight. Both of these studies were cross-sectional in nature and based on self-report. The study we report here is based on weight measured within a clinic setting and, consequently, not subject to the potential biases of self-reported weights. Our study is also based on white, middle-class women. It is unknown if these results would generalize to all populations, but we have no reason to believe they would not.

A growing body of literature supports the appropriateness of the Institute of Medicine gestational weight gain guidelines for achieving optimal birth weights.^10,23,24 The findings presented here support the appropriateness of the Institute of Medicine guidelines for preventing the development of obesity associated with childbearing, assuming that the guidelines are adhered to. The results from this study are important, as excess weight gain and failure to lose pregnancy weight by 6 months postpartum are simple and important markers for risk of subsequent obesity. Clinicians should be aware of weight gain recommendations and encourage pregnant women to adhere to these guidelines. Clinicians should also encourage women to lose pregnancy weight by 6 months postpartum. Women who gain more than the recommended amount or who fail to lose the weight they gained during pregnancy should be referred to successful clinical or community weight loss programs.

References

1. Mokdad AH, Serdula MK, Dietz WH, Bowman BA, Marks JS, Koplan JP. The spread of the obesity epidemic in the United States, 1991-1998. JAMA 1999;282:1519-22.

2. Russell A, Remington P, Rumm P, Haase R. Increasing prevalence of overweight among Wisconsin adults, 1989-1998. WMJ 2000;993:53-6.

3. Folsom AR, Kaye SA, Sellers TA, Hong CP, Cerhan JR, Potter JD, et al. Body fat distribution and 5-year risk of death in older women. JAMA 1993;269:483-7.

4. Willett WC, Manson JE, Stampfer MJ, Colditz GA, Rosner B, Speizer FE, et al. Weight, weight change and coronary heart disease in women. Risk within the 'normal' weight range. JAMA 1995;273:461-5.

5. Manson JE, Willett WC, Stampfer MJ, Colditz GA, Hunter DJ, Hankinson SE, et al. Body weight and mortality among women. N Engl J Med 1995;333:677-85.

6. Launer LJ, Harris T, Rumpel C, Madans J. Body mass index, weight change and risk of mobility disability in middle-aged and older women. The epidemiologic follow-up study of NHANES I. JAMA 1994;271:1093-8.

7. Williamson DF, Kahn HS, Remington PL, Anda RF. The 10-year incidence of overweight and major weight gain in US adults. Arch Intern Med 1990;150:665-72.

8. Institute of Medicine. Nutrition during pregnancy. Part I, weight gain; part II; nutrient supplements. Washington, DC: National Academy Press, 1990.

9. Keppel KG, Taffel SM. Pregnancy-related weight gain and retention: Implications of the 1990 Institute of Medicine guidelines. Am J Public Health 1993;83:1100-3.

10. Parker JD, Abrams B. Differences in postpartum weight retention between black and white mothers. Obstet Gynecol 1993;81:768-74.

11. Scholl TO, Hediger ML, Schall JI, Ances IG, Smith WK. Gestational weight gain, pregnancy outcome, and postpartum weight retention. Obstet Gynecol 1995;86:423-7.

12. Boardley DJ, Sargent RG, Coker AL, Hussey JR, Sharpe PA. The relationship between diet, activity, and other factors, and postpartum weight change by race. Obstet Gynecol 1995;86:834-8.

13. Ohlin A, Rossner S. Maternal body weight development after pregnancy. Int J Obes 1990;14:159-73.

14. Forsum E, Sadurskis A, Wager J. Resting metabolic rate and body composition of healthy Swedish women during pregnancy. Am J Clin Nutr 1988;47:942-7.

15. Parham ES, Astrom MF, King SH. The association of pregnancy weight gain with the mother's postpartum weight. J Am Diet Assoc 1990;90:550-4.

16. Schauberger CW, Rooney BL, Brimer LM. Factors that influence weight loss in the puerperium. Obstet Gynecol 1992;79:424-9.

17. Howell DC. Statistical methods for psychology. Rev ed. Boston: Duxbury Press, 1987.

18. Greene GW, Smiciklas-Wright H, Scholl TO, Karp RJ. Postpartum weight change: How much of the weight gained in pregnancy will be lost after delivery? Obstet Gynecol 1988;71:701-7.

19. Rookus M, Rokebrand P, Burema J, Deurenberg P. The effect of pregnancy on the body mass index 9 months postpartum in 49 women. Int J Obes 1987;11:609-18.

20. Gunderson EP, Abrams B. Epidemiology of gestational weight gain and body weight changes after pregnancy. Epidemiol Rev 1999;21:261-75.

21. Sampselle CM, Seng J, Yeo S, Killion C, Oakley D. Physical activity and postpartum well-being. J Obstet Gynecol Neonatal Nurs 1999;28:41-9.

22. Boardley DJ, Sargent RG, Coker AL, Hussey JR, Sharpe PA. The relationship between diet, activity, and other factors, and postpartum weight change by race. Obstet Gynecol 1995;86:834-8.

23. Cogswell ME, Serdula MK, Hungerford DW, Yip R. Gestational weight gain among average-weight and overweight women-what is excessive? Am J Obstet Gynecol 1995;172:705-12.

24. Schieve LA, Cogswell ME, Scanlon KS. An empiric evaluation of the Institute of Medicine's pregnancy weight gain guideline by race. Obstet Gynecol 1998;91:878-84.

Address reprint requests to: Brenda L. Rooney, PhD, Gundersen Lutheran Medical Center, 1836 South Avenue, La Crosse, WI 54601; E-mail: brooney@gundluth.org

Received December 10, 2001.
Received in revised form March 15, 2002.
Accepted April 4, 2002.