Fat mass deposition during pregnancy using a four-component model

Estimates of body fat mass gained during human pregnancy are necessary to a ssess the composition of gestational weight gained and in studying energy r equirements of reproduction. However, commonly used methods of measuring bo dy composition are not valid during pregnancy. We used measurements of tota l body water (TBW), body density, and bone mineral content (BMC) to apply a four-component model to measure body fat gained in nine pregnant women. Me asurements were made longitudinally from before conception; at 8-10, 24-26, and 34-36 wk gestation; and at 4-6 wk postpartum. TBW was measured by deut erium dilution, body density by hydrodensitometry, and BMC by dual-energy X -ray absorptiometry. Body protein was estimated by subtracting TBW and BMC from fat-free mass. By 36 wk of gestation, body weight increased 11.2 +/- 4 .4 kg, TBW increased 5.6 +/- 3.3 kg, fat-free mass increased 6.5 +/- 3.4 kg , and fat mass increased 4.1 +/- 3.5 kg. The estimated energy cost of fat m ass gained averaged 44,608 kcal (95% confidence interval, -31,552-120,768 k cal). The large variability in the composition of gestational weight gained among the women was not explained by prepregnancy body composition or by e nergy intake. This variability makes it impossible to derive a single value for the energy cost of fat deposition to use in estimating the energy requ irement of pregnancy.