Critical periods of maternal weight gain: Effect on twin birth weight

OBJECTIVE: Our purpose was to evaluate the association between maternal weight gain and twin birth weight. STUDY DESIGN: This historic cohort study was based on 646 live-born twin births of ≤28 weeks from Baltimore, Maryland, Miami, Florida, and Ann Arbor, Michigan. The sum of twin-pair birth weight was modeled as a function of either net maternal weight at delivery or rates of maternal weight gain with use of multiple regression. RESULTS: Birth weight was significantly associated with weight gain before 20 weeks in underweight women, before 20 weeks and after 28 weeks in overweight women, and during all three gestational periods in normal-weight women. Weight gain before 20 weeks had the largest effect on infants of underweight women, less of an effect on infants of normal-weight women, and half as much effect on infants of overweight women. Weight gain after 28 weeks significantly affected the infant birth weights of normal-weight and overweight women, but the effect was half as great among infants of the latter group. CONCLUSIONS: These findings suggest that weight gain during critical periods of gestation significantly influences twin birth weight; these critical periods vary by maternal pregravid weight status.