BODY-FAT AND WATER CHANGES DURING PREGNANCY IN WOMEN WITH DIFFERENT BODY-WEIGHT AND WEIGHT-GAIN

Objective: To determine the fat deposited during pregnancy in women ga ining according to recommendations of the Institute of Medicine and th e relationship of weight gain to fat gain in women of different starti ng weights (classified by their body mass index). Methods: A cohort st udy of healthy, nonsmoking women, 18-36 years of age, identified durin g prenatal visits at three hospital clinics and one birthing center in New York City. From a pool of 432 eligible volunteers who signed a co nsent form, body composition measurements were performed on 200 women at weeks 14 (+/-2) and 37+ of pregnancy, and bone mineral mass was mea sured at 2-4 weeks postpartum Body fat was estimated with a model that used total body water, weight, and density and bone mineral mass. Res ults: In women gaining as recommended by the Institute of Medicine, fa t gains during pregnancy for women underweight, normal weight, overwei ght, or obese before pregnancy were 6.0 +/- 2.6 kg, 3.8 +/- 3.4 kg, 3. 5 +/- 4.1 kg, and -0.6 +/- 4.6 kg, respectively. Higher weight gain in creased fat gain. Body water gain was not different among the four pre pregnancy weight groups. Conclusion: Recommended weight gain should no t cause obesity in any weight group. Underweight women will normalize their body composition if they gain as recommended, whereas obese wome n will have little or no change in body fat. A majority of women do no t gain as recommended during pregnancy. (C) 1997 by The American Colle ge of Obstetricians and Gynecologists.