Interpregnancy Weight Change and Adverse Birth Outcomes: Cohort Study Using Brazil's Routine Register‐Based Linked Data

The effects of interpregnancy weight change (IPWC) on the risk of adverse birth outcomes in subsequent pregnancies are still not fully understood. Existing studies present conflicting results regarding the association between IPWC and preterm birth, while evidence of its relationship with low birth weight (LBW) or macrosomia is limited, particularly in low- and middle-income countries. This population-based longitudinal study used Brazil's routine register-based linked data from 2008 to 2015 to evaluate the association between IPWC and adverse birth outcomes in a subsequent pregnancy. Preterm birth, LBW, and macrosomia were compared across categories of IPWC between pregnancies (including changes in BMI unit, changes in BMI category, and percentage of weight change). Logistic and multinomial logistic regressions were used to estimate the association between IPWC and adverse birth outcomes. We analysed 15,570 live births from 7785 multiparous women. Women who reduced their BMI between pregnancies had an increased chance of delivering preterm neonates (OR 1.27; 95% CI 1.01-1.60) and those who increased their BMI by ≥ 4 units between pregnancies had an increased chance of macrosomia (OR 1.60; 95% CI 1.21-2.12) compared to those who maintained their BMI. Similar results were observed when IPWC was defined as changes in BMI categories and percentage changes in weight. The results of this study show that IPCW were associated with changes in both the newborn's maturity and size in a subsequent pregnancy. These findings support the need to develop experimental studies on the effects of maternal weight management within and between pregnancies to improve outcomes for both mothers and babies.