What usually makes up the largest component of healthy weight gain by the end of pregnancy

Variability in Weight Gain

The BMI-specific target ranges for pregnancy weight gain are relatively narrow, but a very wide range of gain actually occurs. In a California study, for example, only 50% of the mothers who had an uncomplicated pregnancy with a normal birth-weight infant gained the recommended range of weight, with the remainder gaining more or less. Because a substantial amount of the variation in weight gain is due to physiological variability and prepregnancy BMI, deviation from the recommended range may not necessarily be cause for concern. However, it is especially important to assess the dietary patterns and other behaviors of women whose weight gain is unexpectedly high or low.

Defining gestational weight gain

GWG is a complex and unique biologic phenomenon, which supports the growth and development of the fetus.32 GWG is made up of maternal components (including fat mass, fat-free mass, and total body water), placenta components (including placental weight, placental growth, placental development, and placental composition), and fetal components (amniotic fluid and fetal growth; both fat mass and fat-free mass).32 The total amount of weight gained in normal-term pregnancies differs from woman to woman.32 However, some generalizations can be made about the patterns of GWG and the impact on pregnancy outcome. Data from singleton pregnancies in the United States suggested that adult women with a recommended BMI who delivered at full term had a GWG ranging from 10.0 to 16.7 kg, whereas adolescents had a higher GWG (14.6–18.0 kg).32 There was also an inverse association between maternal prepregnancy BMI and GWG; the higher the BMI, the lower the total GWG.32 The pattern of GWG also differs by trimester of pregnancy and is generally higher in the second trimester.32

There are multiple factors that contribute to the amount of weight gained during pregnancy, which may explain some of the differences observed in the patterns of weight gain between subgroups of the population. Potential determinants of gestational weight gain include social and environmental factors (e.g., culture, family, and living environments), maternal factors (e.g., genetics, ethnicity, and comorbidities), and energy balance.32 A summary of the determinants, and interactions between determinants, is shown in Fig. 13.1.

Abstract

Excessive gestational weight gain (GWG) has significant public health implications due to the increased risk of birth complications and cesarean section, and ultimately, increased rates of long-term obesity for the mother. Furthermore, exceeding GWG recommendations is harmful to the offspring as well, conferring increased risk of childhood and adult obesity. This suggests that pregnancy is a critical period of time to affect weight outcomes across generations. Unfortunately, the majority of US women exceed the Institute of Medicine guidelines for recommended GWG. In this chapter, we discuss prenatal physical activity, including current recommendations, pregnant women’s levels of activity, and interventions to attempt to improve engagement. In addition, we discuss other predictors of GWG, evidence for GWG interventions, and recommendations for future approaches.

Changes in Maternal Body Composition and Weight Gain

Gestational weight gain usually follows a sigmoid curve. Approximately 5% of the total weight gain occurs during the first trimester of pregnancy and the remainder 95% is gradually gained at an average rate of about 0.45 kg per week during the second trimester and 0.40 kg per week during the third trimester. The average total weight gain in full-term healthy primigravidas is about 12 kg although the amount of weight gain varies widely among women. Total weight gain is inversely related to maternal prepregnancy body mass index. Mean total weight gain during a full-term pregnancy ranges between 10 and 16.7 kg in normal weight adult women and is lower than 11 kg in overweight and obese women. Higher total weight gains normally occur in adolescent women, in thin women, and in twin or multiple pregnancies. Current recommendations of weight gain during pregnancy are set according to prepregnancy maternal weight for height categories. A normal weight gain during pregnancy is more likely to be associated with optimal reproductive outcome, fetal and infant growth, and development.

Two major components contribute to weight gain during pregnancy: the products of conception (fetus, amniotic fluid, and placenta) and the accretion of maternal tissues (expansion of blood volume and extracellular fluid, enlargement of uterus and mammary glands, and increased adipose tissue). Of the total weight gain, the fetus accounts for ~ 27%, amniotic fluid 6%, and the placenta 5%. Maternal tissue accretion contributes mainly with fat deposition (average 27%, although highly variable between women). The majority of the maternal fat deposited during pregnancy is subcutaneous. In healthy pregnant women, fat appears to be deposited mainly in the hips, back, and upper thighs. This pattern of fat deposition appears to be unique of pregnancy. Fat deposition occurs mainly during the first 30 weeks of gestation under progesterone stimulation. This early fat deposit acts as an energy store for late pregnancy and during lactation. The increase in fat-free mass during pregnancy represents mainly an increase in body water. The amount and pattern of gestational weight gain are strongly influenced by changes in maternal physiology and metabolism and by placental metabolism.

24.7 Preventive Strategies Start In-Utero

Because GWG of the mother is known to be an important predictor of obesity later on in the child; prevention strategies could start early in the fetal life by assuring that the mother gains weight as per the BMI-specific GWG recommendations in accordance with current IOM 2009 guidelines [28]. Further, healthy weight gain and healthy lifestyle habits could optimize pregnancy outcomes and prevent GDM. This reduces the chances of having an LGA baby, which itself increases future risk of obesity.

Based on the majority of prenatal lifestyle intervention studies, however, have definite conclusions that suggests prevention of excessive GWG that may be linked to lower incidence of high birth weight cannot be established. However, all of these studies had the primary outcome of preventing excessive GWG and were underpowered to see the effect on the secondary outcome of preventing high infant birth weight. The study by Mottola et al. reported that, in overweight women, a significantly lower percentage of babies born weighing between 4 and 4.5 kg was found in the group following intense lifestyle intervention to control GWG, compared to controls (3.2% versus 18%, resp.; P = .048) [29]. The most effective way of preventing excessive GWG is not clear, but a combination of prenatal interventions including nutritional counseling, supervised PA sessions, and a behavioral change approach might be the most successful.

Importantly, SGA babies with rapid postnatal weight gain are at very high risk for future obesity and demands preventive strategies at this step by promoting breastfeeding and delaying introduction of complementary foods and high-protein intake diet during early childhood.

11.4.2 Gestational Weight Gain

The optimal pattern of gestational weight gain is not known. In 1990 the U.S. Institute of Medicine (IOM) report concluded that gestational weight gain was an important determinant of fetal growth and set guidelines for weight gain in women of different prepregnancy BMIs [54]. These guidelines were updated by the IOM in 2009 [55] based on a review of a large body of primarily observational evidence of the relationship between gestational weight gain and short- and long-term health outcomes for the mother and child. However, women often gain gestational weight outside the recommended ranges, and there is evidence that the prevalence is increasing [56], even in the United States where the IOM guidelines are promoted [57, 58]. This has raised concerns about the consequences of excess gestational weight gain, including the long-term effects it may have on the offspring [55, 56]. There is strong observational evidence to support an association between greater gestational weight gain and increased child obesity. In 1044 mother-child pairs from Project Viva, the offspring of mothers who had higher gestational weight gain were more likely to be overweight at the age of 3 years (OR: 1.30, 95% CI: 1.04, 1.62 for each 5 kg weight gained) [58]. Adjustment for a range of confounding factors, including glucose tolerance and duration of breastfeeding, made little difference to this finding, but adjustment for parental BMI strengthened the association (OR: 1.66, 95% CI: 1.31, 2.12).

The impact of excess gestational weight gain on offspring obesity risk is also evident in later childhood years, adolescence, and adulthood. In a metaanalysis of 12 studies [59], stratified by offspring life stages of < 5 years, 5–18 years, and 18 + years, the offspring of women who had excess gestational weight gain were 1.4 times (95% CI: 1.23–1.59) more likely to develop obesity than the offspring of women whose gestational weight gain was adequate. The offspring of women who gained inadequate gestational weight had a lower risk of developing obesity (RR = 0.86; 95% CI: 0.78–0.94). The associations were similar regardless of offspring life stage, suggesting that excess gestational weight gain is associated with offspring obesity in both the short and long term. A study of 2432 Australians attempted to quantify the relationship between gestational weight gain and offspring adiposity, and found that offspring at 21 years of age were 0.3 kg/m2 heavier for each 0.1 kg per week greater gestational weight gain, and these associations were independent of maternal prepregnancy BMI [60].

However, the association between gestational weight gain and child obesity risk may be complex. Some evidence suggests that maternal BMI may have an interactive effect on the association between gestational weight gain and child obesity, and this may be different according to child life stages. For example, Oken and colleagues have also shown effects of gestational weight gain on offspring overweight in older children, aged 9–14 years [61]. Before taking account of maternal BMI, a U-shaped relationship was described between gestational weight gain and adolescent adiposity, such that higher rates of obesity were observed in adolescents born to mothers in the lowest and highest categories of weight gain. This is consistent with findings in mother-daughter dyads from the Nurses Health Study II where low and high gestational weight gains were both associated with obesity in the daughters studied at the age of 18 years [62]. However, the role of maternal BMI differed between these two studies. In the younger population, adjustment for maternal BMI changed the association, resulting in a positive linear relationship between gestational weight gain and child BMI, such that low gestational weight gain was associated with a lower risk of offspring obesity. In contrast, the U-shaped relationship found in older adolescents was not changed by taking account of maternal BMI [62]. An important finding from the Nurses Health Study II was that there was an interactive effect of weight gain and maternal BMI, as the association between low and high gestational weight gain and obesity in the daughter was modest among women of normal weight but more marked among mothers who were overweight before pregnancy.

More recent evidence also points toward differential effects of the rate of gestational weight gain at different periods in pregnancy. In a metaanalysis of four studies, higher rates of gestational weight gain in early and midpregnancy consistently had stronger adverse effect on offspring obesity outcomes [63]. For example, a UK study of 5154 mother-child pairs found that greater gestational weight gain during the first 14 weeks of pregnancy was associated with greater child adiposity at 9 years [64]. Similar findings were observed in a Dutch study of 5908 mother-child pairs where greater early pregnancy weight gain was associated with higher child BMI and fat mass at 6 years, and these findings were independent of maternal weight gain before pregnancy and weight gain during other trimesters [65]. The optimal pattern of gestational weight gain has yet to be defined. Not all studies have shown an effect of weight gain on adiposity in the offspring [47, 49], and further studies are needed to determine how variations in the pattern and the amount of weight gained in pregnancy impact on childhood body composition.

Gestational Weight Gain

The optimal pattern of gestational weight gain is not known. In 1990 the U.S. Institute of Medicine (IOM) report concluded that gestational weight gain was an important determinant of fetal growth and set guidelines for weight gain in women of different BMI [50]. However, gestational weight gain is often outside the recommended ranges, even in the United States where the IOM guidelines are promoted [51, 52]. Excessive gestational weight gain is common and there is evidence that prevalence is increasing [53]. This has raised concerns about its consequences, including long-term effects it may have on the offspring [53, 54].

A number of studies have described an effect of gestational weight gain on offspring body composition. For example, among 1044 mother-child pairs studied in Project Viva, child overweight at the age of 3 years was associated with greater gestational weight gain (OR 1.30, 95% CI: 1.04, 1.62 for each 5 kg weight gained) [52]. Adjustment for a range of confounding factors, including glucose tolerance and duration of breast-feeding, made little difference to this finding, but adjustment for parental BMI strengthened the association (OR 1.66, 95% CI: 1.31, 2.12). Using the 1990 IOM recommended ranges of weight gain, 51% of mothers in this cohort gained excess weight, 35% adequate weight, and 14% inadequate weight. When compared with children whose mothers had an inadequate weight gain in pregnancy, children whose mothers had adequate or excessive weight gains had a higher BMI at the age of 3 years, and their risk of being overweight at this age was increased four-fold.

Oken and colleagues have also shown effects of gestational weight gain on offspring overweight in older children, aged 9 to 14 years [55]. Before taking account of maternal BMI, a U-shaped relationship was described between gestational weight gain and adolescent adiposity, such that higher rates of obesity were observed in adolescents born to mothers in the lowest and highest categories of weight gain. This is consistent with findings from the Nurses Health Study II where low and high gestational weight gains were both associated with obesity in the daughters studied at the age of 18 years [56]. However, the role of maternal BMI differed between these studies. In the younger population, adjustment for maternal BMI changed the association, resulting in a positive linear relationship between gestational weight gain and child BMI. In contrast, the U-shaped relationship found in older adolescents was not changed by taking account of maternal BMI [56]. An important finding from the Nurses Health Study II was that there was an interactive effect of weight gain and maternal BMI, as the association between low and high gestational weight gain and obesity in the daughter was modest among women of normal weight but more marked among mothers who were overweight before pregnancy.

The optimal pattern of gestational weight gain has yet to be defined. Not all studies have shown an effect of weight gain on adiposity in the offspring [43, 45], and further studies are needed to determine how variations in the pattern and the amount of weight gained in pregnancy impact on childhood body composition.

Recommended Weight Gain in Pregnancy

The target weights for gestational weight gain (GWG) were based on the recommendations provided by the Institute Of Medicine (IOM), ACOG and National Institute of Diabetes Digestive and Kidney Diseases (NIDDK) [9–12]. Obese women (BMI>30 kg/m2) were recommended a total weight gain of 5–9 kg in pregnancy and a mean weight gain of 0.22 kg/week (0.18–0.27 kg) in the second and third trimesters [10]. The recommendations were based on evidence from population-based cohort studies that evaluated the association between weight gain in pregnancy for women with various BMI and maternal and foetal outcomes. The risk of adverse outcomes varies with the various classes of obesity I (BMI 30–34.9 kg/m2), II (BMI 35–39.9 kg/m2) and III (BMI≥40 kg/m2). The risk of adverse outcomes was minimal for a GWG of 4.5–15.5 kg for obesity class I and 0–4.1 kg for obesity classes II and III. The NICE in United Kingdom refrained from providing recommended ranges for weight gain due to limitations in the evidence and concerns about the generalisability of the results to the UK population.

Underweight

Prepregnancy underweight and insufficient gestational weight gain have been considered as individual risk factors for the occurrence of miscarriage, PTB, intrauterine growth restriction (IUGR), and hypertensive disorders.71 A recent systematic review and meta-analysis72 has shown that the birthweight of children of mothers with anorexia nervosa is lower by 0.19 kg compared with children of mothers at a healthy weight A population study from the same authors has also shown that eating disorders are associated with increased odds of receiving fertility treatment and subsequent twin births.73 Women with anorexia nervosa were more likely to have an unplanned pregnancy and to have mixed feelings about the unplanned pregnancy.

In underweight women and in those at a healthy weight, the risk for macrosomia can be halved if women lost more than 1 BMI unit between pregnancies, but at the same time, the risk for LBW doubled.65

27.5.3 Antepartum Care

As mentioned previously, excessive gestational weight gain can have a compounding effect on the already-increased risks for obese women. In a recent comprehensive systematic review and meta-analysis of over 1.3 million pregnancies in international cohorts, investigators calculated ORs and absolute risk differences (ARDs) for multiple outcomes.30 The study found that excessive weight gain (i.e., over 2009 IOM-recommended amounts) among obese women was associated with higher risk of having large-for-gestational-age (LGA) infants, defined in most studies as birth weight greater than 90th percentile, with an OR of 1.63 (95% CI 1.56–1.70) and an ARD of 7% (95% CI 5%–8%). Obese women also had increased odds for macrosomia (OR 1.83, 95% CI 1.52–2.22) and cesarean delivery (OR, 1.22, 95% CI 1.05–1.42).30 Other studies over the years have demonstrated some compelling evidence that excessive gestational weight gain increases the risk for abnormal glucose metabolism during pregnancy, leading to increased risk of GDM, as well as increased risk for hypertensive conditions during pregnancy.31

Unfortunately, women with obesity are more likely to gain excessive weight during pregnancy as compared to their normal-weight counterparts; the challenge in counseling obese women about the risks of weight gain is significant, but the importance cannot be overstated. As with any counseling, patients also should be aware of potential risks. In considering the potential risks of weight loss or insufficient weight gain during pregnancy, one study demonstrated that obesity was associated with small-for-gestational-age (SGA) risk, and this risk increased with gestational weight gain below guidelines and with weight loss.30 However, importantly, weight loss among obese women was also associated with 5% lower risk for LGA and macrosomia, and cesarean delivery risk was 4% lower.30

The risk-benefit ratio tends to favor close management of weight gain during pregnancy to remain within the IOM-recommended guidelines. Multiple professional societies have produced guidelines recommending calculation of BMI at the first visit and using it to begin the discussion about benefits of avoiding excessive weight gain. This discussion should include a plan for diet and exercise counseling, as indicated by the woman’s current BMI and her current knowledge, skills, and attitudes related to lifestyle modification. Evidence for recommended lifestyle modifications will be cited later in this chapter.