Low Gestational Weight Gain and Risk of Adverse Perinatal Outcomes in Obese and Severely Obese Women

Background: Our objective was to estimate associations between gestational weight gain z scores and preterm birth, neonatal intensive care unit admission, large- and small-for-gestational age birth, and cesarean delivery among grades 1, 2, and 3 obese women. Methods: We included singleton infants born in Pennsylvania (2003–2011) to grade 1 (body mass index 30–34.9 kg/m2, n = 148,335), grade 2 (35–39.9 kg/m2, n = 72,032), or grade 3 (≥40 kg/m2, n = 47,494) obese mothers. Total pregnancy weight gain (kg) was converted to gestational age-standardized z scores. Multivariable Poisson regression models stratified by obesity grade were used to estimate associations between z scores and outcomes. A probabilistic bias analysis, informed by an internal validation study, evaluated the impact of body mass index and weight gain misclassification. Results: Risks of adverse outcomes did not substantially vary within the range of z scores equivalent to 40-week weight gains of −4.3 to 9 kg for grade 1 obese, −8.2 to 5.6 kg for grade 2 obese, and −12 to −2.3 kg for grade 3 obese women. As gestational weight gain increased beyond these z score ranges, there were slight declines in risk of small-for-gestational age birth but rapid rises in cesarean delivery and large-for-gestational age birth. Risks of preterm birth and neonatal intensive care unit admission were weakly associated with weight gain. The bias analysis supported the validity of the conventional analysis. Conclusions: Gestational weight gain below national recommendations for obese mothers (5–9 kg) may not be adversely associated with fetal growth, gestational age at delivery, or mode of delivery.