Deborah B. Ehrenthal1, 2, Cynthia S. Minkovitz3 and Donna M. Strobino3
(1)
Departments of Internal Medicine and OB/GYN, Christiana Care Health System, Newark, NJ, USA
(2)
Departments of Internal Medicine and OB/GYN, Thomas Jefferson University, Philadelphia, PA, USA
(3)
Department of Population, Family and Reproductive Health, Bloomberg School of Public Health, Johns Hopkins University, 615 N Wolfe St., Baltimore, MD 21205, USA
Donna M. Strobino
Email: dstrobin@jhsph.edu
Abstract
Obesity has reached epidemic proportions among women of childbearing age. Prepregnancy obesity and inappropriate gestational weight gain (GWG) have detrimental consequences for maternal health, birth outcomes, and infant growth in the first year of life. Dietary interventions during pregnancy have a modest, although significant, impact on GWG, but their long-term impact is unknown. Studies of interventions to reduce obesity prior to pregnancy are limited, but these interventions have the potential to address modifiable behavioral, social, and environmental factors that may predispose women and their infants to excessive weight gain and to establish healthy trajectories in weight for both.
Keywords
ObesityOverweightGestational weight gainMaternal healthNewborn healthInfant growthInterventions
Key Points
· Obesity and inappropriate weight gain during pregnancy have a detrimental effect on women’s health and birth outcomes, and may affect infant growth in the first year of life.
· Interventions that address obesity among women prior to pregnancy are limited, but have the potential to improve women’s health, birth outcomes, and predispose children to optimal health, healthy weight and physical activity.
· Dietary interventions during pregnancy have a modest, although significant, impact on gestational weight gain, but their long term impact is unknown.
· Pregnancy provides an important opportunity to instill and reinforce positive lifelong habits for women and their infants.
Introduction
Obesity has reached epidemic proportions among women of childbearing age in recent years [1]. Increases in the percentage of children who are overweight or obese have added to the concern about the epidemic in adults [2]. In particular, current trends suggest that children are becoming heavier at younger ages. Although the most recent data suggest a tapering off of trends among adults [3, 4], the transition from overweight to obese is particularly a problem from adolescence into early adulthood [5], the prime childbearing years among most US women, especially among racial and ethnic minorities [6]. These latter groups also suffer more overweight or obesity than their more advantaged counterparts [7, 8]. These trends have important implications for the health and well-being of women during pregnancy and the health of their newborns and infants.
In more recent years, the public health and medical communities have recognized important links between prepregnancy obesity, gestational weight gain (GWG), and adverse outcomes for both the mother and child. Prepregnancy obesity increases the likelihood of developing pregnancy complications [9]. Beyond pregnancy, postpartum retention of weight gained during pregnancy appears to play an important role in the development of adult obesity for women during their childbearing years [10–12]. In addition, the vertical transmission of obesity risk from mother to child is now recognized as important in childhood obesity; an understanding of the factors influencing this risk is evolving [13]. As potentially modifiable risks, achievement of optimal prepregnancy weight and GWG is now viewed as a strategy to improve outcomes for both women and their children, especially among obese women and their offspring, both of whom are at greatest risk for important short- and long-term adverse outcomes.
The objective of this chapter is to evaluate the evidence for the relation between prepregnancy weight, with emphasis on overweight and obesity, and maternal and newborn outcomes and growth of children in the first year of life. It also describes the evidence related to gestational weight gain and these same outcomes. Evaluation of interventions before pregnancy to reduce obesity and during pregnancy to promote optimal weight gain also is discussed. The limitations of the scientific evidence are considered along with future research needs. Finally, the implications of the research are discussed within a life course framework, which addresses the complexity of the determinants of obesity and our ability to stay the increasing trend in rates.
The Overweight/Obese Mother
Overweight and obesity at the start of pregnancy have important implications for outcomes for the mother and the newborn, including the risk of developing pregnancy complications as well as adverse neonatal outcomes [9, 14]. In addition to a consistent association of prepregnancy BMI with outcomes related to birth weight and fetal growth, a higher incidence of birth defects and stillbirth has been reported for obese women [15–17]. Some data suggest an increase in the risk of shoulder dystocia, likely related to the higher birth weight, but this relation has not been consistently identified [18]. Finally, children of overweight or obese mothers appear to be more likely to become obese children. Most of these findings come from observational studies. Assessment of outcomes related to effective interventions, as discussed below, is needed to support causality.
Outcomes for the Child
There is strong and consistent evidence that prepregnancy body mass index (BMI) is directly and independently related to birth weight [13, 19]. The 2013 systematic review and meta-analysis by Yu et al. evaluated the findings of 34 observational studies, including those with cohort, case–control, and cross-sectional designs, and examined the relation of prepregnancy BMI with size for gestational age, low birth weight (LBW), and macrosomia [20]. In nearly all studies, obese women were relatively protected from delivery of a small for gestational age (SGA) or LBW baby, but the odds of large for gestational age (LGA), high birth weight, or macrosomia were increased. For example, the authors reported a 67 % greater odds of macrosomia for women who were overweight prior to pregnancy and greater than a 3-fold increase if the mother was obese [20]. Analysis of outcomes of the well-characterized prospective cohort from the Hyperglycemia and Adverse Pregnancy Outcomes (HAPO) study suggests that the association of obesity and birth weight is independent of a diagnosis of gestational diabetes mellitus (GDM), common among obese mothers [21].
Similar findings were reported by Black et al., who conducted a retrospective study of women enrolled in a large prepaid group-practice managed health care plan [22]. They concluded that, in this population, prepregnancy overweight and obesity contributed significantly to the fraction of babies born LGA, independent of GDM [22]. The findings from both studies suggested that the effects of obesity and GDM on outcomes were additive.
Evidence from observational studies supporting a link between maternal obesity and child obesity continues to accumulate [13, 14, 20]. Of the factors identified during infancy, maternal prepregnancy obesity appears to make the greatest contribution to the risk of obesity during childhood [13, 23–25]. Observational studies, however, are unable to distinguish whether or not there is an independent role of maternal adiposity on the child’s future obesity risk. Whether the link between maternal obesity and child obesity is the result of a shared susceptibility, the effect of the fetal intrauterine environment, postnatal factors, or a combination of factors is not yet clear. All or a portion of the obesity link may be due to behavioral and environmental factors passed from mother to child or within the context of family and community, especially with regard to cultural preferences in food choices and perceptions of a healthy baby.
Outcomes for the Mother
In their 2012 review, Marshall and Spong described the current literature regarding obesity-related maternal pregnancy complications [9]. Evidence points to an increase in gestational diabetes, gestational hypertensive disorders, and thromboembolic disease among obese women compared to women with normal weight at the start of pregnancy [9, 26, 27]. For example, in the large population-based study of Danish women by Ovesen et al., there was a stepwise increase in gestational diabetes risk with increasing degree of obesity; women with a BMI of 35 kg/m2 or more, had an 11-fold greater odds of gestational diabetes when compared to women of normal weight [18]. At delivery, obese mothers are more likely to experience labor dystocia and deliver by cesarean section [28].
Interventions Among Women of Childbearing Age
An optimal approach to improving obesity-related outcomes in mothers and their newborns is to achieve a more healthy weight prior to pregnancy. This goal should be incorporated into the care of women during their reproductive years, through both primary well women care, which incorporates the notion of reproductive awareness, and a discussion of pregnancy planning. As noted above, obese women present a particularly challenging set of concerns because their weight affects not only their health but that of their future offspring. While interventions to alter lifestyle behaviors focused on diet and physical activity among women of childbearing age may be theoretically ideal [14], research in this area is very limited, often due to questions about which women to study and because most studies include small samples [29], with modest results at best [30]. Most studies of women of childbearing ages have focused on those in the older range of the childbearing population [31, 32] and with children [33, 34] although a few studies involve the inter-pregnancy period. Two major prepregnancy interventions specific to obese women are bariatric surgery and the use of insulin-sensitizing drugs.
Bariatric surgery is not the first line of interventions for weight loss but may be recommended if other attempts at weight loss have failed. It has risen in frequency, however, in recent years among women in the childbearing ages, mirroring in part the rise in obesity in the United States [35]. Its use among adolescent females has plateaued in recent years [36], perhaps in part due to controversies about the appropriateness of surgery for this age group. Bariatric surgery procedures most commonly induce food intake restriction, food malabsorption, or both [37], and in turn promote weight loss, an average of about 30 % in the first year following surgery, although the majority of patients remain overweight [38].
Maggard and colleagues undertook a systematic review of studies of the impact of bariatric surgery on subsequent fertility and pregnancy outcomes [39], followed by more recent reviews by Guelinckx, Devlieger and Vansant, and Kjaer and Nilas [38, 40]. They note that these studies are necessarily observational in nature. The design, sample characteristics, control groups, and type of surgery [41] evaluated are quite heterogeneous across studies [38–40]. Controls among pregnant women may include births to the same women before and after surgery, women who are matched by weight with and without surgery, and in one recent study an additional control group of pregnant women who were the same weight as women with surgery at the time the surgery was performed [42]. Most studies show reduced maternal complications, as measured by GDM and hypertension, and in rates of macrosomic births. Birth weight may be reduced, and there is some suggestion of an increase in SGA births, but this finding is by no means consistent across studies [38–40]. Choice of an appropriate control group remains a challenge in this research.
While the studies of births in women who undergo bariatric surgery generally show that it is safe with some conflicting findings, there may be problems for women with malabsorption and who are at risk for micronutrient deficiencies [40]. Whether or not these deficiencies contribute to birth defects, particularly neural tube defects, is unclear due in part to the difficulty in obtaining adequate samples because of their rare occurrence [40]. Timing of pregnancy is important following surgery especially with regard to potential nutritional deficiencies, and it is recommended that women wait at least 1–2 years following surgery before conception [43]. Nutritional evaluation both before and during pregnancy is recommended to address these risks [38, 39, 43].
A second prepregnancy intervention is the use of insulin-sensitizing drugs for weight loss. Nieuwenhuis-Ruifrok et al. reviewed data from 14 trials of obese or overweight women who were given insulin-sensitizing drugs for weight loss [44]. All but two of the studies included samples of women with polycystic ovary syndrome (PCOS); only data for women completing the trials were included in the analysis. Metformin over 1,500 mg/day was associated with a significant decrease in BMI among overweight and obese women with PCOS; there were no significant findings for lower dosages, but numbers in these studies were small. No additional impact was noted when included with lifestyle interventions. The review had several limitations; only women who completed the trials were included in the analysis, the objectives for the trials were designed with different primary outcomes and clinical questions, the samples across studies were quite heterogeneous, and most studies had small sample size. Moreover, extension of the findings to obese or overweight women prepregnancy without PCOS is unclear.
Studies which address dietary intervention, physical activity, or counseling related to obesity and weight loss are few in young nonpregnant women of childbearing age [29]. The few available studies were conducted among limited populations or women who already have young children and who are unlikely to have subsequent births [33, 34, 45]. The lack of data about potential interventions in young women of childbearing age is a serious gap in the literature. It represents a missed opportunity from a life course perspective and provides clinicians with limited options to prevent obesity or reduce weight gain or high prepregnancy weight among women to whom they provide well woman or preconception care.
Gestational Weight Gain and the Overweight/Obese Woman
Recommendations for GWG have evolved over the past several years as the obesity epidemic has changed the distribution of risk factors for adverse perinatal outcomes and highlighted the importance of balancing the short- and long-term risks for mothers and their children. The link between GWG and birth weight was observed decades ago, and efforts to prevent LBW guided health care and public policy recommendations for GWG [46]. The 1970 Institute of Medicine (IOM) report recommended a 20–27 lb weight gain for all women. Ensuring adequate nutrition for women became a major focus of maternal health interventions.
However, trends in GWG for US populations now show an increasing percentage of women gain in excess of current GWG recommendations [47]. There are important variations in GWG among racial and ethnic groups in the US population [48]. In their review, Headen et al. found excess GWG was most common among. White mothers (>50 %), while inadequate GWG was more common among Asian, Hispanic, and Black mothers [48]. Data from Pregnancy Risk Assessment and Monitoring System (PRAMS) suggest that obese women tend to gain less weight overall than nonobese women, but they are more likely to gain in excess of the current IOM recommendations for their weight [49]. Within the context of the current epidemic of obesity, these differences underscore the importance of understanding the relation of GWG to adverse outcomes.
Components of GWG
Weight gain during pregnancy is a function of a number of factors including maternal weight gain, fetal weight gain, placental weight, and fat mass [47]. The increase in fat mass shows the greatest variability between women and is most reflective of both gestational weight gain and prepregnancy obesity [49]. GWG typically varies by trimester, with a rapid increase in maternal stores during the second trimester preceding the rapid growth of the fetus during the third trimester [49]. Because weight gain in the third trimester is linked closely with the length of pregnancy, it must be taken into account in research on the relation of GWG with preterm birth and low birth weight (LBW).
Determinants of GWG
Weight gain during pregnancy is greatest during the first pregnancy and among pregnancies with multiple gestations (e.g. twins, triplets) [49]. Several maternal factors influence GWG, including prepregnancy BMI, parity, height, smoking, as well as level of education and comorbid conditions [50]. Race and other social and cultural factors also appear to play an important role [50]. Pregnancy-related factors also potentially influence GWG. For example, improvement in diet prompted by a new diagnosis of gestational diabetes may result in weight loss [51]. Conversely, women with a gestational hypertensive disorder may gain more weight as a result of fluid retention and edema related to the syndrome. The influence of bed rest on GWG is unexplored [52].
Current US GWG Guidelines
The medical and public health communities have struggled to define recommendations for GWG. Initially, recommendations focused on the importance of adequate weight gain to prevent LBW. The 1990 IOM revision of recommendations for GWG in the United States reflected the understanding that a mother’s adiposity prior to pregnancy influenced fetal growth, and recommendations for GWG were tailored based on prepregnancy BMI, an easily measured value reflecting a proxy for the degree of maternal obesity at the start of gestation. The importance of both short- and long-term outcomes for the mother and child was recognized, but little evidence was available to support recommendations. In addition, there was little evidence that weight gain counseling had an impact on GWG.
The new guidelines for GWG released in 2009 by the IOM were based on a systematic review of the literature (Table 10.1) [47–49]. The recommendations were considered in the context of the recent rise in obesity among women of childbearing age and their children. Evidence of greater GWG among the diverse populations of US mothers was of concern, as was the increasing incidence of obesity-related maternal complications including cesarean delivery, higher rates of fetal macrosomia, and concerns about the impact of GWG on future obesity risk for both the mother and child. To arrive at their recommendations, the committee tried to balance the risks and benefits to the neonate as well as to the mother [47, 49].
Table 10.1
Current IOM recommendations for GWG [49]
|
Prepregnancy BMI |
Total weight gain |
Rates of weight gain, second and third trimester |
||
|
Range in kg |
Range in lb |
Mean (range) in kg/week |
Mean (range) in lb/week |
|
|
Underweight (<18.5 kg/m2) |
12.5–18 |
28–40 |
0.51 (0.44–0.58) |
1 (1–1.3) |
|
Normal weight (18.5–24.9 kg/m2) |
11.5–16 |
25–35 |
0.42 (0.35–0.50) |
1 (0.8–1) |
|
Overweight (25.0–29.9 kg/m2) |
7–11.5 |
15–25 |
0.28 (0.23–0.33) |
0.6 (0.5–0.7) |
|
Obese (≥30 kg/m2) |
5–9 |
11–20 |
0.22 (0.17–0.27) |
0.5 (0.4–0.6) |
BMI body mass index
The 2009 recommendations changed most significantly for women who are overweight or obese prior to pregnancy. These most recent guidelines recommend gains between 15 and 25 lbs for women who are overweight (BMI 25–29.9 kg/m2) and 11 and 20 lbs for women with a BMI in the obese range (BMI 30 kg/m2 or more). Recommendations for teen mothers are not different from those for adult women. It was recommended that short women gain at the lower end of the range. The committee did not have evidence that recommendations should differ based on mother’s race or ethnicity, although they do differ for women with multiple gestation pregnancies [47, 49].
With the release of their recommendations, the IOM suggested strategies to help women adhere to GWG recommendations. Pregnancy is now viewed as a teachable moment, a time in women’s lives when they may be more motivated to make lifestyle and other changes. Helping women achieve an optimal GWG presents an opportunity to impact short- and long-term outcomes for both the mother and her child. If excess GWG plays an independent role in the development of obesity, focused efforts to avoid excess GWG would be warranted. As discussed below, there is little or no experimental evidence to demonstrate that interventions, which effectively limit GWG, improve long-term outcomes for the mother.
Evidence Linking GWG to Outcomes for Overweight and Obese Mothers and Their Babies
Nearly all evidence supporting the link between GWG and outcomes for mothers and their offspring come from observational studies of women across the BMI spectrum. Although these studies consistently demonstrate several important significant associations between GWG and several short- and long-term outcomes [53], they are constrained by failure in most studies to account for the correlation of weight gain with length of pregnancy and increasing fetal weight as a component of weight gain. Maternal obesity is defined as a BMI of 30 kg/m2 or more prior to pregnancy; this group is traditionally further divided into three groups: class I (BMI 30–34.9 kg/m2), class II (35–39.9 kg/m2), and class III (40+ kg/m2). The few studies large enough to focus specifically on obese women suggest that the severity of obesity influences the relation of GWG to outcomes [54, 55]. In this section, we summarize the evidence of a relation for short- and long-term outcomes for women who enter pregnancy overweight or obese.
Short-Term Outcomes
Birth Weight
Observational studies show that inadequate GWG increases the odds of SGA, and moderate evidence shows that excess GWG is linked to LGA [53]. These studies may overestimate the effect because most fail to subtract babies’ weight from total weight gain; the resulting part-whole correlation between the component of weight gain of the fetus and birth weight necessarily overestimates this relation. Kramer and colleagues showed a similar problem when studying preterm birth, which is further compounded by changes in velocity of weight gain over gestation [56]. Recent studies of large cohorts of women, including obese women suggest these associations are stronger for women of normal weight. Among women who are obese, excess GWG is linked to a greater risk of LGA and macrosomia, whereas inadequate weight gain shows a less strong relation with SGA and LBW [57, 58].
Maternal Outcomes
Overweight and obese women are more likely to develop pregnancy complications including gestational diabetes and hypertensive disorders of pregnancy [9]. Results from the EDEN mother-child cohort suggested that net GWG was directly related to the development of gestational hypertension [59]. Findings from investigations exploring the relation of GWG to the development GDM have been mixed [60, 61]. The relation of GWG to other outcomes may be different for women with pregnancy complications, potentially because the diagnosis may prompt lifestyle changes that may affect overall weight gain [51]. For women entering pregnancy obese, interventions during the prenatal and postpartum periods may also mitigate these risks and improve long- and short-term outcomes for mothers and their children. Key targets for intervention include optimizing GWG, encouraging postpartum weight loss, as well as working to address maternal and infant factors that might play a role in setting children’s trajectory towards a healthy weight as they grow.
Prenatal Interventions to Reduce Maternal Weight Gain
Prenatal interventions generally address reduction or restriction in weight gain during pregnancy among samples of pregnant women in general as well as samples of overweight or obese women. The interventions focus primarily on diet, physical activity, and lifestyle alone or in combination. Some studies also evaluated whether additional strategies are needed such as goal setting related to weight loss to enhance the impact of diet and lifestyle interventions. The evidence supporting these interventions is not strong, although it is most consistent for dietary interventions among normal weight women.
Thangaratinam et al. provide the most comprehensive review and meta-analysis of studies of interventions in pregnancy and their impact on maternal weight gain [62, 63]. Their review evaluated 44 randomized controlled trials of interventions related to diet, physical activity, and lifestyle. The results of the meta-analysis show a modest effect of the interventions on reducing weight gain but with considerable heterogeneity across studies. Among the 34 trials evaluating GWG, the impact of any intervention, regardless of the specific intervention, was estimated to result in a reduction of −1.42 kg with 95 % confidence intervals (−0.95; −1.89 kg). The ten trials of dietary interventions alone showed the largest impact with estimates of reduced weight gain of −3.84 kg (−2.45; −5.22 kg) [62]; they also showed the largest effect of all interventions on BMI at delivery, when assessed [63]. The reduction in GWG in the 14 trials of physical activity was modest, −0.72 kg (−1.20; −0.25 kg), as well as in the mixed intervention trials, −1.06 kg (−1.67; −0.46 kg). A small but statistically significant reduction was noted in birth weight in the 28 trials with newborn data. A significantly reduced odds of preeclampsia was shown in 6 trials of dietary interventions and of GDM in 3 trials of dietary interventions. Mixed interventions showed no effect on preeclampsia or GDM, and neither maternal outcome was evaluated in trials of physical activity [62, 63].
The evidence related to weight gain was graded by Thangaratinam et al. as modest, but the overall quality of the evidence for an impact on GDM and gestational hypertension was low [62, 63]. Studies varied by sample characteristics, whether they included overweight or obese women or women of all prepregnancy weight and whether additional components were evaluated such as goal setting. All studies were constrained by selection of women in prenatal care with attendant effects on external validity. Few studies evaluated the impact of the intervention on postpartum weight retention, infant growth, or whether there were real, sustained changes in diet.
The review by Thangaratinam and colleagues included all women regardless of prepregnancy weight [62, 63]. Oteng-Nini et al. reviewed 13 randomized clinical trials and 6 non-randomized studies of prenatal dietary, physical activity, and behavioral and lifestyle interventions among overweight and obese pregnant women [64]. They reported a decrease of −2.21 kg (−2.86; −1.59 kg) in ten trials in which GWG was studied as well as a suggestion of a reduced rate of GDM in studies in which it was evaluated. They found no evidence of a reduction in LGA births. The overall quality of the studies was assessed as low to moderate. The results of a review by Dodd and colleagues also suggested no impact of dietary interventions on LGA births among overweight and obese women [65]. Although they found that women in seven trials gained significantly less weight in the dietary intervention group, adjustment for heterogeneity among studies using random effects models resulted in nonsignificant differences.
Some studies have also evaluated whether interventions may be effective in reducing excessive weight gain during pregnancy [66, 67]. Ronnberg and Nilsson evaluated studies of interventions to reduce excessive GWG and found the evidence to be of insufficient quality to develop recommendations for clinical practice [68]. In an alternative approach, Brown et al. reviewed five studies of goal setting in combination with modifications in diet, physical activity, or both [69]. Although goal setting appeared to be useful to women, the impact of specific aspects of goal setting was unclear.
The results reported by Thangaratinam and colleagues are similar to other reviews conducted on specific interventions [68–72], suggesting some promise for the dietary interventions in particular but limited impact overall of interventions to reduce GWG. There are a number of gaps in the literature, particularly failure to evaluate the long-term impact of the interventions on women or their infants, as noted above. Studies also lack theory or conceptual models to support the interventions from a behavioral modification perspective [70], although some attention was given to goal-setting strategies as a component of the intervention [69]. There is also limited information about specific interventions, making it difficult to replicate studies or to develop clinical practice recommendations. Studies are needed with adequate samples to evaluate the reasons for heterogeneity of findings across studies and to evaluate whether there are subgroups of women who would benefit most from specific interventions. In addition, it is reasonable to postulate that dietary interventions which result in close to a 4 kg reduction in weight gain may also reduce postpartum weight retention, but the magnitude of the impact may be small over the life course of a woman if the intervention does not result in long-term change in diet or alter whether or not a woman becomes overweight or obese.
Maternal Prepregnancy BMI Associated with Decreased Initiation and Shorter Duration of Breastfeeding
High prepregnancy BMI can adversely effect breastfeeding rates. Despite Healthy People 2020 Goals [73], recommendations of the American Academy of Pediatrics [74], and widespread recognition of the benefits of breastfeeding, the percentage of women who breastfeed in the United States did not meet the Healthy People 2010 goals. Among all births in the United States in 2006, 74 % of mothers ever breastfed and 44 % continued through 6 months of age. The corresponding the American Academy of Pediatrics similarly recommends exclusive breastfeeding through 6 months of age and continued breastfeeding for 1 year or longer as complementary foods are introduced and as mutually desired by mother and infant [74].
In a review of the literature, Wojicki reported 12 studies of breastfeeding initiation; the results of 9 studies showed an association between overweight and obesity prior to pregnancy and failure to initiate breastfeeding [75]. Of the 12 studies that considered duration, 10 reported an association between maternal overweight or obesity and decreased duration. Among 2 of the 9 studies of breastfeeding initiation and 2 of the 10 focusing on duration, these relations were observed for selected subgroups, although most studies did not stratify analyses by race and ethnicity. Wojicki suggests that differences by race and ethnicity may reflect underlying sociocultural, environmental, or physiological factors and that these factors are important to address in interventions to promote breastfeeding.
Most studies of breastfeeding have not considered the role of medical complications. Kistantis et al. conducted a study that stratified analyses by presence or absence of medical and delivery complications (e.g., hypertension, fetal distress, gestational diabetes, meconium) [76]. The study results showed that decreased initiation and duration was limited to overweight or obese women with complications. Wojicki noted that possible reasons underlying the association between obesity and breastfeeding may relate to biological changes (delayed prolactin response), mechanical issues (positioning the infant), behavioral factors (choice and intentions), and psychological factors [75].
In a Belgian retrospective cohort study of 200 women, Guelinckx et al. reported decreased initiation and duration of breastfeeding among both obese and underweight women with no association between initiation and hypertensive disorders [77]. More recently, in a sample of 550 women participating in the Pregnancy, Infection, and Nutrition Postpartum Study, Mehta and colleagues confirmed the link between prepregnancy overweight and obesity and reduced initiation and duration of breastfeeding [78]. Most importantly, they found that these relations were not mediated by depressive symptoms, perceived stress, or anxiety during pregnancy.
Although the association between obesity and decreased initiation and breastfeeding well established in the literature, there is little understanding of the underlying mechanisms. While primary efforts are needed to reduce obesity, further studies also are needed to understand the underlying mechanisms in order to determine whether interventions should address mutable factors that may increase breastfeeding among obese women. These factors may include anatomic barriers that require support of breasts to facilitate appropriate latch-on, reduced willingness to seek support for breastfeeding that requires enhanced and targeted outreach, and concerns over body image which might necessitate strategies to promote comfort of breastfeeding in public [77]. In the absence of studies, it is difficult to understand the barriers to breastfeeding among obese women.
Maternal Prepregnancy BMI and Gestational Weight Gain Influence Infant Growth at 1 Year
In addition, to birth outcomes discussed previously, prepregnancy weight also is associated with infant postnatal growth. Growth in the first year of life is of particular interest given the association between rapid early growth and subsequent childhood obesity [79–81] and cardiovascular disease and diabetes in adulthood [82, 83]. In addition, growth in the first year of life reflects the establishment of early feeding, physical activity, and sleep practices which, when unfavorable, may contribute to the development of obesity in later childhood. Numerous studies have also determined early growth rate to be a strong predictor of childhood obesity [84].
Using data from the Pregnancy, Infection, and Nutrition Study, Deierlein et al. reported that prepregnancy overweight and obesity were associated with greater weight for age and weight for length at 6 months, but not with length for age, after accounting for other infant and maternal characteristics [85]. The relations were attenuated, however, when birth weight was taken into account in the analysis, the effect of prepregnancy overweight and obesity on growth indices at 6 months were largely explained by the relation of prepregnancy weight with prenatal growth.
With regard to body composition, Chandler-Laney et al. observed that prepregnancy BMI was also associated with a child’s total lean mass, but not total fat mass or trunk fat mass at 12 months, after adjusting for infant length and rate of weight gain in the first year [86]. The authors speculate that the association may be attributed to genetic susceptibility or the intrauterine environment. Total and trunk fat mass, in their study, was associated with weight gain in the first year of life, particularly in the first 6 months; this association is of particular interest given the role of rapid weight gain in early infancy on future body composition and fat deposition.
Data from the Pregnancy, Infection, and Nutrition Study also inform our understanding of the relation of GWG to infant growth [87]. Infants born to women with GWG up to 199 % of the 2009 Institute of Medicine (IOM) recommendations had higher weight for age and length for age z-scores between birth and 3 years of age than women with appropriate GWG, while infants born to women with GWG of 200 % or more of the recommendations experienced higher weight for age, length for age, and weight for length z-scores. These findings were first observed in early infancy and persisted through 3 years of age. Also, these associations remained after adjusting for prepregnancy BMI, maternal diabetes prior to pregnancy, and demographic characteristics. The authors note that “in utero programming effects beyond fetal growth” may contribute to persistent faster rates of growth as might the postnatal feeding environment (e.g., feeding behaviors, diet quality) and genetic susceptibility to rapid growth.
Multiple studies suggest that increased GWG in pregnancy is associated with higher growth parameters in the first year of life, through adolescence and into adulthood. The extent to which the accompanying adiposity, hypertension, and lipid abnormalities that track into adulthood are related to subsequent obesity, in utero exposures, or genetic susceptibility remains unclear. Moreover, the association of GWG with childhood BMI and adiposity likely varies by prepregnancy BMI status with inconsistent results reported, although generally stronger relations are found among women who are under or normal weight [13, 88]. Gillman argues that prepregnancy BMI, rather than GWG, is a more relevant, modifiable factor and suggests further need to understand the different components of weight gain during pregnancy including maternal tissue, fluid accumulation, the placenta, and the fetus [89]. Chandler-Laney explored the role of GWG in predicting lean mass at 12 months and found no association independent of prepregnancy BMI [86], while others, as reviewed by Poston, have reported associations between GWG and greater fat mass later in childhood and adulthood [90].
Further work is needed to understand the independent effects of prepregnancy BMI and GWG on infant growth and body composition in order to design more effective interventions [91]. A two pronged approach of optimizing the health of women prior to pregnancy and assuring appropriate weight gain during pregnancy may be needed to improve pregnancy outcomes and assure that infants start life on a healthy trajectory with regard to nutritional and metabolic status.
Conclusion
Obesity is widely recognized to be associated with multiple chronic diseases and to adversely affect women’s health across the life course, regardless of pregnancy status. As discussed in this chapter, obesity and inappropriate weight gain during pregnancy have detrimental consequences for women’s health, birth outcomes, and infant growth in the first year of life. Reducing obesity prior to pregnancy has the potential to address modifiable behavioral, social, and environmental factors that may predispose both women and their infants to excessive weight gain and to establish healthy trajectories that are more likely to achieve healthy weight for both. It also has potential to decrease health care utilization by decreasing the incidence of chronic conditions resulting from obesity-related effects in the mother such as gestational hypertension and diabetes.
Interventions that address obesity among women prior to pregnancy are limited to date but have the potential to improve women’s health, improve birth outcomes, and predispose children to optimal health, healthy weight, and physical activity. Interventions that address GWG may have additional positive impacts but may be too little or too late and should be considered as adjunct therapies in addition to addressing maternal obesity. If these interventions, particularly related to diet and physical activity, have long-term impact including behavior change, then they should be part of a life course strategy to maintain healthy weight in women. Long-term evidence, however, is not available.
Pregnancy provides an important opportunity to instill and reinforce positive lifelong habits for women and their infants, particularly among women who have not been receiving routine health care services. The Affordable Care Act, which promotes delivery of preventive services through a yearly well women visit without copayments or other cost sharing mechanisms for women, provides an important opportunity to deliver more regular health care services to women prior to pregnancy. This approach includes an opportunity to recognize and address obesity among women of childbearing age.
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