cal composition and accretion rates of maternal, placental, and fetal components of GWG are presented, followed by discussions of the maternal and fetal-placental physiology underlying weight gain in pregnancy. Lastly, pathophysiologic conditions that may adversely affect GWG are reviewed to provide a foundation for understanding changes in body weight and composition during pregnancy.

TOTAL AND PATTERN OF GESTATIONAL WEIGHT GAIN

Total Gestational Weight Gain

The total amount of weight gained in normal-term pregnancies varies considerably among women. Nevertheless, some generalizations can be made regarding tendencies and patterns of GWG in singleton and multiple pregnancies.

Singleton Pregnancies

An examination of studies published in the United States from 1985 to the present indicate that the mean total GWG of normal weight adult women giving birth to term infants ranged from a low of 10.0 to a high of 16.7 kg (Appendix C [Tables C-1A and C-1B] contains a tabular summary of the studies examined by the committee). Among adolescents, in general, GWG tended to be higher compared with adult women (means ranged from 14.6 to 18.0 kg in the studies examined). A consistent finding across studies was an inverse relationship between GWG and pregravid body mass index (BMI). Figure 3-2 illustrates a similar relationship with data derived from Abrams et al. (1986).

Since the release of the report Nutrition During Pregnancy (IOM, 1990) and its guidelines for GWG, a number of studies have examined GWG among overweight and obese women. Bianco et al. (1998) found that the mean GWG for 613 obese (BMI > 35) women averaged 9.1 ± 7.4 kg. Thirteen percent of the women, however, gained more than 16 kg, and 9 percent either lost or failed to gain weight. 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), and small-for-gestational age (SGA) outcomes was 4.6-11.4 and 0-4.1 for class I and II obesity, respectively; and weight loss of 0-4.1 kg for class III obesity (Kiel et al., 2007) (see Chapter 2 for definition of obesity classes).

A prospective study of a cohort of 245,526 Swedish women confirmed that GWG among obese women (BMI = 30-34.9) and very obese women



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