Weight Gain During Pregnancy Reexamining the Guidelines (2009) / Chapter Skim
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3 Composition and Components of Gestational Weight Gain: Physiology and Metabolism
3 Composition and Components of Gestational Weight Gain: Physiology and Metabolism
Pages 71-110
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From page 71... ...
Next, the unique chemi TOTAL AND OVERALL PATTERN OF GESTATIONAL WEIGHT GAIN Mother Fetus Fat-free mass Fetal growth Fat mass -Fat-free mass Placenta -Fat mass Amniotic fluid indicates possible causal influences FIGURE 3-1 Schematic summary of components of gestational weight gain. 71 Figure 3-1.eps
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From page 72... ...
In a cohort study using birth certificate data from 120,251 obese women in Missouri, 18, 30, and 40 percent of the women gained < 6.8 kg in obese classes I, II, and III, respectively. The amount of total gain associated with minimal risk for preeclampsia, caesarean delivery, large-for-gestational age (LGA)
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FIGURE 3-2 Birth weight as a function of maternal weight gain and prepregnancy weight for height. Figure 3-2.eps SOURCE: Modified from Abrams and Laros (1986)
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Outcomes associated with GWG in twin pregnancies, as with singleton pregnancies, are a function of pregravid BMI. Several studies have shown that, when stratified by pregravid BMI, increased GWG is associated with increased twin birth weight among underweight, normal weight, and overweight, but not obese, women (Brown and Schloesser, 1990; Luke et al., 1992; Lantz et al., 1996)
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. The following discussion summarizes the committee's review of the evidence on rate of GWG in singleton and twin pregnancies; observed relationships between GWG pattern and prepregnancy BMI; and birth weight outcomes associated with varying patterns of GWG in twin pregnancies.
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in all groups except for obese women; and mean gains in the second and third trimester were higher in underweight and normal weight women than in overweight and obese women. Birth weight was correlated most strongly with gain in the second trimester (32.8 g/kg GWG versus 18 and 17 g/kg in the first and third trimesters, respectively)
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Maternal Components of Gestational Weight Gain The committee reviewed evidence on maternal total body water (TBW) accretion, fat-free mass (FFM)
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(2003) also found that total body water accretion was positively correlated with birth weight, in agreement with other investigations (Langhoof-Roos et al., 1987; Lederman et al., 1997; Mardones-Santander et al., 1998; Butte et al., 2003)
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From page 79... ...
. Fat Mass: Fat Accretion Based on serial measurements of skinfold thickness at seven sites made in 84 healthy, pregnant women, fat appears to be deposited preferentially over the hips, back, and upper thighs up to about 30 weeks' gestation (Figure 3-4; Taggart et al., 1967)
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Skinfold measurements lack the precision necessary to estimate changes in fat mass accurately. Two-component body composition methods based on TBW, body density, and TBK are invalid during pregnancy because of the increased hydration of FFM that occurs during pregnancy; the constants for hydration, density, and K content of FFM used in two-compartment models are not applicable to pregnant women and would lead to erroneous estimations of FFM and FM.
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. Gains in total body water and fat mass and gestational weight gain also are presented by compliance with the IOM 1990 recommendations for weight gain: women gaining less than (n = 51)
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12 9 6 3 0 Pregravid 9 wk 22 wk 36 wk Gestational Period FIGURE 3-6 Changes in body weight and composition of 63 women (low pregravid BMI n = 17; normal pregravid BMI n = 34; high pregravid BMI n = 12) measured at 9, 22, and 36 weeks' gestation.
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(1978) demonstrated a linear relationship between fetal growth and placental mass, fetal weight, and placental growth in both early and late gestation; and a significant increase in the mean placental weight
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See Table C-5 in Appendix C for normative criteria for placental weight in singleton, twin, and triplet pregnancies. Placental Growth Normal placental growth using human tissue is difficult to ascertain because placentas obtained from early pregnancy are often the result of an abnormal pregnancy outcome.
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, and IL-6. Hence, the chronic inflammation associated with obesity may affect placental growth and function, thereby altering maternal metabolic function and resulting in the women with pregravid obesity having decreased maternal pregravid maternal insulin resistance and decreased maternal fat accretion but increased placental and fetal growth.
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. The criteria that are commonly used are to classify fetal growth are: • SGA (i.e., birth weight less than the 10th percentile for gestational age)
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birth weight curves based on the 1999 and 2000 United States Natality datasets from 22 through 44 weeks' gestation. Although gestational age is an important factor related to fetal growth, other factors affect not only fetal growth but also the pattern of growth.
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In their study, birth weight was affected by maternal parity and age. Zygosity, fetal gender, chorionicity, fusion of the placentas, placental weight, and site of
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In the third trimester, there is a decrease in individual fetal growth, more so in triplets than in twins, which may be related to placental function. Fetal Body Composition The human fetus at term has a significantly different body composition than most other mammalian species.
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While neonate body composition bore no association with any other measured factor, birth weight correlated positively with prepregnancy weight (r = 0.34) , prepregnancy FM (r = 0.32)
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From page 91... ...
; • prepregnancy BMI, with birth weight significantly greater in neo nates of overweight and obese women than underweight or normal weight women because of increased FM, not FFM (Sewell et al., 2006; Hull et al., 2008) ; • maternal weight gain, which is associated with both increased fetal FFM and increased FM (and maternal pregravid BMI [Catalano and Ehrenberg, 2006]
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From page 92... ...
Polyhydramnios is associated with various fetal structural anomalies such as congenital esophageal atresia, fetal anemia, congenital infections, and maternal diabetes. Given the wide range of normal amniotic fluid volume at term, this compartment may affect maternal GWG by as much as 1 kg.
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Importantly, plasma volume expansion is correlated with clinical performance and birth weight. Poor plasma volume expansion is associated with a poorly growing fetus and poor reproductive performance.
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. Serum adiponectin is lower in the third trimester, a change that correlates with a decrease in insulin sensitivity (Catalano et al., 2006)
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. In women with normal glucose tolerance during pregnancy who lose significant weight postpartum, there is a return to normal metabolic function.
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A Sims, Longitudinal changes in body composition and energy bal ance in lean women with normal and abnormal glucose tolerance during pregnancy, pp.
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Although there is a significant increase in maternal leptin concentrations in early pregnancy (Hauguel-de Mouzon et al., 2006) , most likely related to placental production, the increased leptin concentrations do not appear to be associated differently with energy expenditure or fat accretion between lean and obese women.
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Placental Hormone Production The sex steroids and human placental lactogen (hPL) , which best reflect the endocrine function of the placenta have been considered primary candidates for regulation of maternal insulin sensitivity (Leturque et al., 1989)
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The role of progesterone, hPL, and leptin in maternal insulin sensitivity and energy homeostasis remains to be established; inflammatory mechanisms are novel potential regulatory pathways that will also have to be examined. ABNORMAL MATERNAL METABOLISM Weight Loss During Pregnancy Weight loss or no GWG as a result of dietary caloric insufficiency should induce certain maternal hormonal and metabolic responses.
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There was a chronic increase in ketonemia levels in 12 percent of the controls and 47 percent of the women with GDM. Pregnant women develop ketonemia much earlier than nonpregnant women during prolonged fasting because of the accelerated starvation.
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From page 101... ...
as a result of the metabolic and hormonal changes that occur during pregnancy. Although pregnant women with diabetes are more likely to develop elevated blood ketones than women with normal glucose tolerance, a substantial proportion of pregnant women with normal glucose tolerance have elevated blood ketone levels at some time during gestation.
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7. Gestational gains in weight, total body water, total body potas sium, protein, and FFM, but not FM, are positively correlated with birth weight across all BMI categories.
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Areas for Additional Investigation The committee identified the following areas for further investigation to support its research recommendation. The research community should conduct studies on: • Potential effects of maternal weight loss on components of mater nal body composition for both the mother and the fetus, particu larly in obese women; and • Mechanisms by which placental hormonal factors and systemic inflammation impact the regulation of maternal metabolism during pregnancy.
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1990. Insulin sensitivity and B-cell responsiveness to glucose during late pregnancy in lean and moderately obese women with normal glucose tolerance or mild gestational diabetes.
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2006. Effects of gestational weight gain and body mass index on obstetric out come in Sweden.
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2007. Twin birth weight standards.
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2007. Gestational weight gain and pregnancy outcomes in obese women: how much is enough?
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2003. Body mass index -- specific weight gains associated with optimal birth weights in twin pregnancies.
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2004. Lon gitudinal changes in energy expenditure and body composition in obese women with normal and impaired glucose tolerance.
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1988. New equations for estimating body fat mass in pregnancy from body density or total body water.
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