Using Non-inferiority Margins to Define Optimal Gestational Weight Gain Ranges Based on Reducing the Risk of Occurrence of Adverse Neonatal Outcomes

Abstract Objectives To identify optimal gestational weight gain (GWG) ranges to prevent adverse neonatal outcomes based on the new Brazilian GWG charts. Methods Data from 9,294 women from the Brazilian Maternal and Child Nutrition Consortium and Birth in Brazil study were used. Women aged ≥18 years, free of hypertensive disorders, diabetes in pregnancy, or diseases affecting GWG, were selected. Total GWG was calculated as last measured prenatal weight minus self-reported pre-pregnancy weight. Total GWG was standardized to gestational age-specific z scores according to the Brazilian GWG charts. A composite outcome was defined as the occurrence of any of small-for-gestational-age birth (SGA, birthweight < 10th percentile), large-for-gestational-age birth (LGA > 90th percentile) according to INTERGROWTH-21st charts, or preterm birth (birth < 37 weeks). We weighted each outcome in a composite index using previously-published weights to account for its relative seriousness. Logistic and Poisson regressions were performed with GWG z scores as exposure and independent outcomes and the composite outcome, respectively. Models were adjusted for maternal age, education, pre-pregnancy BMI, and smoking during pregnancy. GWG ranges associated with the lowest risk of the composite outcome were identified using the non-inferiority margins approach (20%). Results The median total GWG was 12.5 kg (IQR 9–16), and 6.2% of the neonates were SGA, 16.6% LGA, and 10.5% were preterm. Higher GWG z scores were associated with an increase in LGA probabilities and preterm birth compared with neonates born with appropriate weight and ≥37 weeks, respectively. Lower z scores were associated with an increase in SGA probability. The non-inferiority margins analysis showed that to prevent the occurrence of these adverse outcomes, women with underweight, normal-weight, overweight, or obesity should gain between 6.5–14.1 kg, 6.4–13.8 kg, 2.2–12.1 kg, and –2.2–8.9 kg, respectively. Conclusions Total GWG ranges associated with lower risk of adverse neonatal outcomes were identified using non-inferiority margins. The next step must incorporate maternal outcomes in this analysis. Funding Sources Brazilian National Research Council, Brazilian Ministry of Health, Bill and Melinda Gates Foundation.