Point of diminishing returns: when does gestational weight gain cease benefiting birthweight and begin adding to maternal obesity?

This study is a reanalysis of the first scientific paper published by one of the authors, originally coauthored with Dr. Roy H. Petrie. In honor of Dr. Petrie, these data have been reanalyzed to re-evaluate the data using more sophisticated techniques and to expand on the original findings. This reanalysis examines the contribution of maternal weight gain to infant birthweight and retained maternal weight in the immediate postpartum period, and the effect of weight gains below, at, and above the Institute of Medicine (IOM) guidelines on both infant birthweight and retained maternal weight in the postpartum period. The study population included 487 term, uncomplicated, singleton pregnancies. Body mass index (BMI) was calculated for each woman, and categorized as underweight, normal weight, or overweight. Maternal retained weight was calculated as postpartum weight 2 days after delivery minus pregravid weight. Every kilogram of gestational weight gain increased birthweight by 44.9 g for underweight women, 22.9 g for normal weight women, and 11.9 g for overweight women. For every kilogram of retained weight, birthweight was increased by 35.6 g for underweight women, 15.9 g for normal-weight women, and 5.1 g for overweight women. Increasing weight gains from below to equal to IOM guidelines increased birthweight and maternal retained weight by 317 g (11%) (P < 0.01) and 5 kg (P < 0.01), respectively, for underweight women; 141 g (4.4%) (P < 0.02) and 6.2 kg (P < 0.01), respectively, for normal-weight women; and 200 g (6.4%) (NS) and 6.4 kg (P < 0.01), respectively, for overweight women. Increasing weight gains from equal to above the IOM guidelines increased birthweight and maternal retained weight by an additional 299 g (9.4%) (P < 0.02) and 7.3 kg (P < 0.01), respectively, for underweight women; an additional 196 g (5.9%) (P < 0.01) and 5.9 kg (P < 0.01), respectively, for normal weight women; and an additional 9 g (0.3%) (NS) and 8.3 kg (P < 0.01), respectively, for overweight women. These findings suggest that, beyond a certain level of weight gain, there is a point of diminishing returns (increase in birthweight) at the expense of increasing maternal postpartum obesity for the woman who has gained excessively.