Association of maternal pre-pregnancy body mass index with neonatal respiratory outcomes: a nationwide population-based cohort study

To assess the association of maternal pre-pregnancy body mass index (BMI) and neonatal respiratory morbidities, including respiratory distress syndrome (RDS), transient tachypnea of the newborn (TTN) and bronchopulmonary dysplasia (BPD). This was a cross-sectional study utilized linked mother-infant records from the Korean National Health Insurance Service for birth cohorts spanning 2014-2021. Maternal BMI measured within three years prior to delivery was collected and categorized as < 18.5, 18.5-22.9 (reference), 23.0-24.9, 25.0-29.9, and ≥ 30 kg/m². Relative risks (RRs) and 95% confidence intervals (CIs) for respiratory morbidities were calculated. Inverse probability of treatment weighting (IPTW) was applied using propensity scores, and weighted generalized linear models were used adjusting for maternal and newborn characteristics. Among 2,285,943 live births, 779,091 neonates were selected for analysis. After adjusting for confounders, infants born to mothers with a BMI ≥ 30 had a higher risk of RDS (RR 2.598; 95% CI 2.523-2.676), TTN (RR 1.154; 95% CI 1.126-1.182), and moderate-to-severe BPD (RR 6.070; 95% CI 3.687-9.994) compared to those born to mothers with normal BMI (18.5-22.9). Conversely, maternal underweight (BMI < 18.5) was associated with reduced risk of RDS (RR 0.873; 95% CI 0.842-0.906), TTN (RR 0.951; 95% CI 0.927-0.975) and BPD (RR 0.371; 95% CI 0.263-0.523). Pre-pregnancy maternal BMI was associated with an increased risk of neonatal respiratory morbidities, highlighting the importance of maternal weight management before and during pregnancy as a potential strategy to enhance neonatal health outcomes.