Interpregnancy Body Mass Index Change and Offspring Mortality Risk following the Second Pregnancy

The aim of the study is to examine the impact of maternal interpregnancy body mass index (BMI) change on subsequent offspring mortality risk.

This is a retrospective cohort study of women who had two consecutive live singleton deliveries of at least 20 weeks' gestation from the Utah Population Database. Our exposure was defined as interpregnancy BMI change from the date of first delivery to the conception date of subsequent pregnancy. We categorized BMI change as: < - 1, -1 to 0, 0 to <1 (reference), 1 to 2, 2 to 4, ≥4 kg/m². Our primary outcome was all-cause age-specific mortality during four time periods: neonatal (≤28 days), infant (29 days to <1 year old), childhood ((≥1 to <5 years old), and late childhood (5 to <18 years old). We also examined mortality specifically attributed to congenital anomalies. Analyses used Cox proportional hazard models stratified by full term (≥37 weeks) and preterm (<37 weeks) deliveries. All models were adjusted for relevant confounders.

Of 266,752 women, among full-term deliveries, women with a BMI increase of 4 kg/m² or more had an increased risk of neonatal mortality in their subsequent pregnancy (hazard ratio or HR = 1.72, 95% confidence interval or CI: 1.23-2.41) Women who lost 1 kg/m² or more between deliveries also had increased neonatal mortality (HR = 1.46, 95% CI: 1.04-2.05). There were no differences in infant, early, or late childhood mortality by interpregnancy BMI change. Maternal interpregnancy interval weight loss of 1 kg/m² or more and weight gain of ≥4 kg/m² also had increased risk of mortality associated with congenital anomalies or conditions arising during the neonatal period following their subsequent delivery.

Women with significant interpregnancy weight gain and modest weight loss have a significant increased risk of neonatal mortality following their subsequent pregnancy.

· Significant weight gain between deliveries increases the risk of neonatal death.. · Modest weight loss between deliveries increases the risk of neonatal death.. · This risk may be partially explained by increased risk of congenital malformations..