Timing of weight gain during pregnancy: promoting fetal growth and minimizing maternal weight retention.

OBJECTIVE: To examine the association of the extent and timing of pregnancy weight gain with infant birth weight (IBW) and postpartum weight retention (PPWR).
DESIGN: Retrospective cohort study of pregnant women followed through 6 weeks postpartum. MEASUREMENTS: Birth weight and maternal weight gain before 20 weeks, 21-30 weeks, 31 weeks to term and postpartum weight retention were measured.
SUBJECTS: A total of 371 healthy white nonsmoking pregnant women followed by the Prenatal Nutrition Counselling Program of the Department of Health and Social Services of the province of Prince Edward Island, Canada, between 1979 and 1989 who had uncomplicated pregnancies resulting in full term singleton infants.
RESULTS: Weight gain during pregnancy (> 12 kg) was associated with PPWR (> 2.5 kg) in underweight, normal and overweight women. Pregnancy weight gain explained 65.2% of the variability in PPWR, but very little of the variability (4.7%) in IBW. Predictors of IBW (gestational age, pregravid weight and infant gender) were not related to PPWR. Early maternal weight gain (< or = 20 weeks) was a strong predictor of PPWR. Comparisons of mothers with PPWR above and below the median of the group indicated important differences in early weight gain (< or = 20 weeks) for underweight (3.3 kg), normal weight (3.3 kg), and overweight (6.2 kg) mothers.
CONCLUSION: The results emphasize the importance of the timing of gestational weight gain and show an advantage in deferring a larger portion of required weight gain to late pregnancy (particularly in well-nourished overweight women) in order to promote fetal growth while reducing the risk of high weight retention and its potential adverse health consequences.