Erica P. Gunderson1
(1)
Division of Research, Kaiser Permanente Northern California, 2000 Broadway, Oakland, CA 94612, USA
Erica P. Gunderson
Email: erica.gunderson@kp.org
Abstract
Over the past decade, women have become heavier at the time of conception, gain more weight during pregnancy, and are a greater risk of postpartum weight retention. Excessive weight gain during pregnancy is a key predictor of postpartum weight retention. Characterizing trends in postpartum weight retention can help to identify high-risk women who are susceptible to substantial weight retention postpartum and accelerated weight gain trajectories in midlife. Understanding postpartum weight trajectories can inform our efforts for primary prevention of obesity and help to reduce long-term obesity and its associated consequences.
Keywords
Gestational diabetes mellitusAtherosclerosisCardiovascular diseaseProspective cohort studiesDiabetesGlucose toleranceEpidemiologyPregnancyWomen
Key Points
· Women are starting pregnancy heavier than ever before.
· Women have higher average weight gains during pregnancy than in past generations.
· The strongest predictors of postpartum weight retention are high maternal body size before pregnancy, excessive gestational weight gain, young age at menarche, and excessive gestational weight gain.
Introduction
Weight gain and becoming overweight during the reproductive years are strong independent predictors of cardiovascular disease morbidity and mortality, particularly among women [1–4]. The hormonal adaptations to pregnancy promote gestational weight gain and fat accumulation to support fetal growth and development, as well as provide energy stores for lactation [5]. Yet, in modern societies, the abundant food supplies and sedentary lifestyles are likely to result in gestational weight gain exceeding optimal levels. Pregnancy’s physiological adaptations may predispose susceptible women to marked postpartum weight retention as triggers for the development of overweight or obesity [6]. Excessive gestational weight gain not only increases the risk of some pregnancy complications (i.e., gestational diabetes mellitus, hypertensive disorders, C-section delivery) but can have lasting adverse effects on women’s health including greater risk of developing the metabolic syndrome, type 2 diabetes, and/or cardiovascular disease in mid- or late life [4, 7, 8]. Moreover, shortened duration of lactation and formula supplementation may compromise postpartum cardiometabolic profiles and increase disease risk [9–12].
Women are starting pregnancy heavier than ever and are gaining more weight during pregnancy than in past generations. Both maternal body mass index (BMI) and gestational weight gain have increased for the general US population during the past three decades. Recent estimates show that 60 % of all US women are overweight or obese (BMI ≥25) and that at least one-third are obese (BMI ≥30) [13]. The secular trends for increasing overweight and obesity prevalence are highest among women aged 35–44 years [13]. From 1960 to 2008, the prevalence of overweight (BMI 25–29.9) and obesity (BMI ≥30) in women of reproductive age increased from 28 to 60 % (Fig. 5.1) [14]. Within the past 20 years, the proportion of women exceeding gestational weight gain recommendations has increased significantly. Excessive gestational weight gain [i.e., above the levels recommended by the Institute of Medicine (IOM) for their BMI category] [15] was reported by 43 % of pregnant women in 2008 compared to 33 % in 1988 (Fig. 5.2) [14]. The increasing proportion of US women who are overweight or obese before pregnancy combined with higher gestational weight gain during pregnancy and more sedentary lifestyle behaviors and short duration of breastfeeding are key contributors to increasing postpartum weight retention and obesity risk among young women.
Figure 5.1
US trends in overweight and obesity in women 1960–2008 (age 20–44 or 20–39 years)
Figure 5.2
Secular trends in gestational weight gain from 1995 to 2009; US Pregnancy Nutrition Surveillance, CDC
Maternal overweight or obesity before pregnancy is the most common high-risk obstetric condition [16] and is associated with greater maternal and infant morbidity, including gestational diabetes and hypertension disorders in the woman as well as neural tube defects, macrosomia, and perinatal mortality in the newborn [17, 18]. Women who are already overweight or obese before pregnancy tend to retain more weight postpartum than those not overweight [19, 20], despite having lower gestational weight gain and larger newborns [21].
Weight gain trajectories before pregnancy may exert a significant influence on the weight gain related to pregnancy, as age at reproductive maturation and genetic characteristics may influence the tendency to retain weight after pregnancy. The American College of Obstetrics and Gynecology (ACOG) recommends modification of maternal weight before conception as well as advice and monitoring of gestational weight gain during pregnancy as measures that may prevent pregnancy complications and adverse long-term outcomes for women and their children [18]. Characterization of the trends in postpartum weight retention and identification of high-risk women who are susceptible to substantial weight retention postpartum and accelerated weight gain trajectories in midlife are important to our understanding of targets for primary prevention of obesity and future chronic disease in young women.
Pregnancy Cohort Studies and Postpartum Weight Retention
A meta-analysis of early and late postpartum weight retention estimated that postpartum weight retention (as measured by BMI) averages 2.5 kg/m2 (about 6 kg) at 6 weeks, 1.25 kg/m2 (about 3 kg) at 6 months, and 0.5 kg/m2 (about 1.25 kg) at 1 year [22]. A major limitation of practically all pregnancy cohort design studies is that they rely on maternal recall of body weight before conception and/or early first trimester weight measurements. Self-report of prepregnancy weight is biased toward underreporting to a greater extent in overweight or obese women and thereby inflate the estimates of postpartum weight retention for high-BMI groups. Pregnancy cohort studies based on self-reported pregravid weight may introduce substantial bias because high-BMI groups underreport body weight by about 5 kg versus 1 kg for other groups [23, 24]. Therefore, reporting bias affects estimates of gestational weight gain and postpartum weight retention to a greater extent for high- than low-BMI groups. An underestimate of 5 kg may overestimate gestational weight gain by almost 50 % for obese women, and an error of 1 kg may overestimate postpartum weight change by more than 100–200 %.
Furthermore, postpartum weight retention may be overestimated in the high-BMI groups due to the higher trajectory of weight gain established before conception that may continue at the similar accelerated pace after pregnancy. Thus, weight retention at 1–2 years postpartum may not be due to retention of gestational gain but weight gain after delivery. Previous studies with serial postpartum weight measurements have distinguished between weight retention and subsequent weight gain by prepregnancy body size [20].
Childbearing Cohorts and Pregnancy-Related Weight Gain
Longitudinal cohort studies focusing on the natural history of childbearing among women of reproductive age suggest that a first birth has adverse effects on overall adiposity, while increasing number of births (parity) has cumulative effects on central adiposity. In CARDIA women, waist circumference increased with each subsequent birth controlling for prepregnancy measurements [25], while body weight increased primarily after the first birth [25, 26]. The findings suggest that the greatest impact on overall fat stores is after the first birth but subsequent births increase central obesity. The Coronary Artery Risk Development in Young Adults (CARDIA) study estimated pregnancy-related weight gain from before to after pregnancy controlling for secular trends in weight gain and to assess differences within prepregnancy BMI (overweight or obese) and parity groups (primiparas) [25]. The unique strengths of this study include the longitudinal design, standardized research measurements of body weight from before to after pregnancy (3- to 5-year intervals), and high retention rates. The large sample size enabled investigators to determine that pregnancy-related weight gain depended on the first birth (primiparity) and by maternal prepregnancy overweight. In CARDIA, postpartum weight retention averaged 1 kg for women who were not overweight before pregnancy (BMI <25) and about 3–6 kg for women who were already overweight or obese before pregnancy (BMI ≥25) controlling for sociodemographics, prepregnancy BMI, and lifestyle factors [25, 27]. Being overweight before pregnancy signifies the predisposition for weight gain, and pregnancy may exacerbate this tendency for many women. The CARDIA study provides most accurate estimates of long-term weight gain due to pregnancy and its aftermath, by accounting for secular trends in weight gain during the same period among women who did not bear children.
Certain lifestyle behaviors are also likely to influence women’s risk of becoming overweight or obesity in midlife [6, 28]. For example, among nonsmokers in CARDIA, giving birth was associated with a twofold greater risk of becoming overweight within several years versus not giving birth [6]. Yet, among smokers, women who had given birth were half as likely to become overweight as those who had never given birth; OR = 0.41(95 % CI: 0.17,0.96) for women delivering one birth only and 0.36 (95 % CI: 0.08,1.65) for women delivering two or more births [6]. Other modifiable risk factors include postpartum sleep, dietary practices, and physical activity, although biological risk factors such age at menarche and primiparity also appear to play key roles.
Pregnancy Cohorts and Estimates of Average Postpartum Weight Retention
A 2011 meta-analysis examined average postpartum weight retention with several time periods [29]. On average, at 6 months or less postpartum, women who experienced gestational weight gain above IOM recommendations retained an average of 4 kg more than those gaining within recommendations. By 6–12 months postpartum, the weight retention averaged 2.5 kg in the group with excessive gestational weight gain. By 3 years postpartum, the retention was estimated to be 3 kg greater. However, these estimates are based on very few studies, in which serial measurements of postpartum weights were not available, and had variable sample characteristics which may explain the higher “retention” for the longer period of follow-up. The variability in estimates of average postpartum weight retention may be related to maternal characteristics such as race, sociodemographics and economic status, age, smoking, and levels of gestational weight gain.
Pregnancy Cohorts and Risk of Substantial Postpartum Weight Retention
Large pregnancy cohort studies (n > 400) generally report that 13–20 % of pregnant women (Table 5.1) experience substantial weight retention by 1 year postpartum (defined as body weight of 5 kg above preconception weight). Substantial postpartum weight retention has been reported among 7–52 % of women at 1 year postpartum when studies including special populations, such as low-income groups and pregnant adolescents, are included. However, the percentages with substantial postpartum weight retention correlate closely with the prevalence of prepregnancy overweight and obesity for the specific cohort. For example, northern European and US cohorts with lower rates of maternal prepregnancy overweight or obesity (7–25 %) reported lower proportion of women with substantial weight retention (10–20 %). The US cohorts that focused largely on women from low socioeconomic groups reported much higher rates of maternal prepregnancy overweight or obesity (24–52 %) and reported the highest proportions of women experiencing substantial postpartum weight retention (20–50 %) [6, 28, 30–33].
Table 5.1
Prepregnancy high BMI (%), excessive GWG (%), and substantial postpartum weight retention (PPWR) (%) at 1–2 years postpartum from cohort studies (n > 400) from 1988 to 2011
|
Author, year |
Sample size (n) |
Age range (years) |
Time of postpartum measurement |
Overweight or obese before pregnancy (%) |
Substantial PPWR ≥5 kg (%) |
|
Country (years data collected) |
|||||
|
Ohlin, 1990 [48] |
1,423 |
17–49 |
12 months |
7c |
14 |
|
Sweden (1971–1984) |
|||||
|
Keppel, 1993a [44] |
2,944 |
>15 |
10–18 months |
10b |
>20 |
|
USA (1988) |
|||||
|
Greene, 1988a [46] |
7,116 |
23 ± 11 |
Variable (between 2 pregnancies) |
24d |
~20 |
|
USA (1959–1965) |
|||||
|
Gunderson, 2001 [20] |
1,300 |
18–41 (mean 27) |
Variable (between 2 pregnancies) |
13b |
>20 |
|
USA (1980–1990) |
|||||
|
Olson, 2003 [33] |
540 |
18 to >40 |
12 months |
41b |
~20 |
|
USA (not stated) |
|||||
|
Gunderson, 2008 [34] |
940 |
33 ± 5 |
12 months |
25b |
13 |
|
USA (1999–2003) |
|||||
|
Siega-Riz, 2010 [31] |
550 |
31 ± 5 |
3, 12 months |
33b |
~40 |
|
USA (2001–2005) |
|||||
|
Rothberg, 2011a [32] |
427 |
14–25 |
12 months |
52 |
~50 |
|
USA (2001–2004) |
|||||
|
Rode, 2012 [30] |
1,840 |
<25 to >36 |
12 months |
20 |
13 |
|
Denmark (1996–1999) |
Substantial PPWR defined as ≥5 kg above prepregnancy weight
aSample includes teenagers
bDefined as BMI ≥26 kg/m2
cDefined as BMI ≥24 kg/m2
dDefined as >120 % of ideal body weight for height
Correlates of substantial postpartum weight retention based on epidemiologic studies include high gestational gain, pregravid overweight, primiparity, black race, low socioeconomic status, smoking cessation, and fewer than 5 h of sleep per day [19, 33, 34]. The strongest predictors of postpartum weight retention include maternal overweight or obesity before pregnancy, excessive gestational weight gain exceeding the IOM recommendations, and primiparity [27, 35, 36]. Maternal characteristics associated with a two- to threefold higher risk of becoming overweight after pregnancy independent of gestational weight gain include young age at menarche (less than 12 years), short interval (less than 8 years) from menarche to first birth, maternal age 24–30 years [28], and short sleep duration (<5 h per 24 h period) at 6 months postpartum [34]. These risk factors may indirectly represent either genetic or biologic influences on adult body weight prior to pregnancy, socioeconomic differences in maternal age when childbearing begins, and/or postpartum behavior changes. Although the strength of associations with postpartum weight retention for these traits is similar to total gestational weight gain, for some risk factors, their lower prevalence in a population may result in relatively lower attributable risk for postpartum weight retention than gestational weight gain or maternal body size.
Risk of Becoming Overweight or Obese After Pregnancy
A two- to threefold greater risk of becoming overweight after pregnancy has been associated with reproductive factors such as excessive gestational weight gain, young age at menarche (<12 years), and pregnancy within 8 years of menarche [28]. Very few studies have examined the risk of becoming overweight due to pregnancy, although some have linked gestational weight gain to weight status more than a decade later [37, 38]. These data suggest that weight gain trajectories may be influenced by genetic factors influencing reproductive maturation and that pregnancy at a young age exacerbates the risk of becoming overweight to the same extent as excessive gestational weight gain.
Evidence from childbearing cohorts and pregnancy cohorts suggests that a first birth and maternal prepregnancy body size are key predictors of long-term weight retention and that gestational weight gain is likely to mediate these associations. The next sections critically examine these risk factors and their impact on weight changes after pregnancy.
Prepregnancy Body Size
Although gestational weight gain is linked to postpartum weight retention, primiparity and larger body size before pregnancy exert important influences that modify these relationships. Evidence that prepregnancy BMI influences weight retention has varied by attributes of the populations studied and the inadequate sample size to assess effect modification by prepregnancy BMI categories in the gestational weight gain and postpartum weight association. Women who are overweight or obese before pregnancy are generally more likely to have excessive as well as inadequate gestational weight gains [21, 39]. Excessive gestational weight gain increases the risk of postpartum weight retention, but the effect may depend on prepregnancy body size, maternal age, and primiparity. Yet, very few studies have addressed the joint effects of these key risk factors. Weight retention or gain following delivery may also be highly variable and strongly influenced by both the weight gain trajectory that preceded pregnancy (i.e., high prepregnancy BMI) and excessive gestational weight gain.
Gestational Weight Gain
In the USA, at least 43 % of all pregnant women [14] and two-thirds of overweight women exceed the recommended amount of weight gain during pregnancy, while one-third of obese women gain more than 25 lb [39–42]. Specifically, overweight and obese women are two to six times more likely to exceed the weight gain recommendations during pregnancy [39, 42, 43] than other BMI groups. They are also predisposed to higher postpartum weight gain and retention after pregnancy [44].
Gestational weight gain is strongly, positively correlated with maternal weight change from preconception to beyond 6 months postpartum and exerts long-term effects on maternal body weight [45–49]. In multiple linear regression models, total gestational gain has accounted for 20–35 % of the variability in the weight change [19, 45, 48, 49]. In the NMIHS cohort, Parker and Abrams found that high gestational gain was associated with a twofold increase in risk of substantial weight gain (above 9 kg) from preconception to 10–18 months postpartum among women who were underweight and normal weight prior to pregnancy [50] but high body size was also directly associated with postpartum weight. Gunderson et al. reported that gestational gain above the recommended levels was associated with a threefold higher risk of becoming overweight after pregnancy (BMI ≥26) among women who were under- or average weight before pregnancy in large, multiethnic cohort [28].
Reproductive Maturation and Timing of Pregnancy
Reproductive maturation, including young age at menarche (<12 years) and pregnancy onset within 8 years of menarche, may increase a woman’s risk of weight retention or becoming overweight after pregnancy [28]. Weight gain trajectories after pregnancy may be influenced by genetic factors or other biological influences from early childhood. These risk factors appear to influence postpartum weight retention as strongly as excessive gestational weight gain and should be incorporated into future studies as a way of refining subgroups for whom weight control during pregnancy has the greatest impact in reducing weight retention.
Pregnancy Weight Gain Triggering Maternal Obesity
The impact of gestational weight gain on risk of substantial postpartum weight retention (>5 kg) and risk of becoming overweight after pregnancy has been reported in only a few studies [28, 48, 51]. Overall, average weight gain related to childbearing among women who became overweight after pregnancy was about 10 kg [28]. Yet, the risk of becoming overweight or obesity due to childbearing is an important outcome to assess the impact on health risk for young women of childbearing age. Specifically, excessive gestational weight gain not only adversely affects perinatal health outcomes but may be the first trigger of obesity in young women [25, 37]. As a potentially modifiable risk factor, gestational weight gain may provide the critical opportunity for slowing the weight gain trajectory in young women that results in midlife obesity.
Fat Accumulation and Body Composition Changes Due to Pregnancy
Total gestational gain is highly variable resulting in large variation between individuals in postpartum weight retention and body fat distribution. During pregnancy about 30 % of gestational weight gain is comprised of fat, with deposition preferentially in the femoral and abdominal regions producing a more gynecoid body fat distribution.
Longitudinal studies of body fat deposition from prepregnancy to postpartum have found differences in body fat deposition by maternal body size. Obese women showed a tendency to develop more central obesity at 6 months postpartum [52]. In 557 healthy women, subcutaneous body fat (skinfold thicknesses) measured from before, during, and 6 weeks after pregnancy reported that central body fat gains in the subscapular area were relatively high during pregnancy and that primiparas gained more fat at both thigh and subscapular locations than other women [53]. Moreover, fat stores in the triceps and thigh regions were utilized to a greater extent within the first 6 weeks postpartum.
A study of 15 women using magnetic resonance imaging (tomographs) to measure subcutaneous and non-subcutaneous adipose tissue from before pregnancy and at four intervals postpartum reported that 68 % of gestational fat gain was deposited in the trunk and that excess fat gain remaining at 1 year postpartum tended to be localized centrally [54]. Data from large, population-based studies are consistent with these findings. Parity has been correlated with higher abdominal girth many years after childbearing with larger waist-hip ratios (WHR) [55–57], and longitudinal studies of childbearing age women found cumulative increases in WHR [26] and waist circumference changes from before to after pregnancies in CARDIA women [25].
Pregnancy and Visceral Fat Changes
Some evidence suggests that pregnancy increases visceral adiposity. In a longitudinal study of 122 premenopausal CARDIA women (50 black, 72 white), adipose tissue (visceral and subcutaneous) compartments were measured via computed tomography from before pregnancy (1995–1996) and again 5 years later (1999–2000). We identified 14 women who gave birth once during the 5-year interval and had adipose tissue measured before and after the birth as well as in 108 women who did not give birth during this same time interval [58]. In multiple linear regression models adjusted for age, race, and changes in total and subcutaneous adiposity, the visceral adipose tissue levels increased by 40 and 14 % above initial levels for the parous and nonparous groups, respectively; group mean difference (95 % Confidence Interval) in visceral fat levels was 18.0 cm2 (4.8, 31.2) controlling for gain in total body fat and covariates, p < 0.01. There was also a borderline greater group difference in mean (95 % CI) waist girth of 2.3 cm (0, 4.5), p = 0.05, that represented an absolute mean increase of 6.3 cm (4.1, 8.5) versus 4.0 cm (3.2, 4.8) for parous versus nonparous group. Thus, pregnancy is associated with preferential accumulation of adipose tissue in the visceral compartment for similar gains in total body fat. Thus, childbearing increases central adiposity to a greater extent than overall adiposity. These findings are important because chronic disease risk is better predicted by central obesity, particularly visceral adiposity, even among nonobese individuals.
Conclusions
Weight gain before, during, and after pregnancy may not only affect maternal and fetal health for current and subsequent pregnancies but may be a primary contributor to future development of obesity in women during midlife and beyond [6, 37, 59]. Identification of high-risk women who may benefit from preconception and prenatal interventions to avoid the accelerated gestational weight gain is the key to prevention of pregnancy-related weight gain and long-term obesity-related chronic disease in women of reproductive age. More information regarding the influence of socioeconomic factors and culture practices, smoking cessation, lactation, and other behaviors on weight changes both during and after pregnancy is also needed.
High prepregnancy body size may be the most important risk factor for pregnancy-related weight retention. Women who are moderately overweight before a first pregnancy may benefit from weight loss several months before pregnancy as well as require additional support during early pregnancy to carefully control gestational weight gain within IOM recommendations. Overweight and obese women who succeed in achieving gestational weight gain within the recommended ranges need additional support for lactation and to promote postpartum weight loss to below preconception weight. Women who begin pregnancy in the normal range, but have excessive gestational weight gain or other risk factors (i.e., gestational diabetes, young age, primiparity, or depression), may benefit from weight control programs during the first year postpartum to reduce weight retention.
Accelerated prepregnancy weight gain trajectories, pregnancy complications, medical conditions, and/or other behaviors among women may predispose them to substantial weight gain and obesity during midlife. Risk assessment is needed to identify the subgroup of women who are predisposed to greater risk of substantial postpartum weight retention or to becoming overweight or obese after pregnancy. Weight gain and development of overweight during the reproductive years are an increasing problem and confer excess risk of cardiovascular disease morbidity and mortality, particularly among women [1–4]. During the life span, cumulative weight gain may eventually lead to development of the metabolic syndrome, type 2 diabetes, and/or cardiovascular disease [4, 7, 8]. As modifiable risk factors, prevention of excessive gestational weight gain and substantial postpartum weight retention during the reproductive years provides a critical opportunity for early obesity and chronic disease prevention efforts among women.
Grant and Acknowledgment
Funding is provided by the National Institute of Diabetes and Digestive and Kidney Diseases (K01 DK059944 and R01 DK090047).
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