Inter-pregnancy Weight Change and Risks of Severe Birth-Asphyxia-Related Outcomes in Singleton Infants Born at Term: A Nationwide Swedish Cohort Study

BACKGROUND Maternal overweight and obesity are associated with increased risks of birth-asphyxia-related outcomes, but the mechanisms are unclear. If a change of exposure (i.e., maternal body mass index [BMI]) over time influences risks, this would be consistent with a causal relationship between maternal BMI and offspring risks. Our objective was to investigate associations between changes in maternal BMI between consecutive pregnancies and risks of birth-asphyxia-related outcomes in the second offspring born at term. METHODS AND FINDINGS This study was a prospective population-based cohort study that included 526,435 second-born term (≥37 wk) infants of mothers with two consecutive live singleton term births in Sweden between January 1992 and December 2012. We estimated associations between the difference in maternal BMI between the first and second pregnancy and risks of low Apgar score (0-6) at 5 min, neonatal seizures, and meconium aspiration in the second-born offspring. Odds ratios (ORs) were adjusted for BMI at first pregnancy, maternal height, maternal age at second delivery, smoking, education, mother´s country of birth, inter-pregnancy interval, and year of second delivery. Analyses were also stratified by BMI (<25 versus ≥25 kg/m2) in the first pregnancy. Risks of low Apgar score, neonatal seizures, and meconium aspiration increased with inter-pregnancy weight gain. Compared with offspring of mothers with stable weight (BMI change of -1 to <1 kg/m2), the adjusted OR for a low Apgar score in the offspring of mothers with a BMI change of 4 kg/m2 or more was 1.33 (95% CI 1.12-1.58). The corresponding risks for neonatal seizures and meconium aspiration were 1.42 (95% CI 1.00-2.02) and 1.78 (95% CI 1.19-2.68), respectively. The increased risk of neonatal seizures related to weight gain appeared to be restricted to mothers with BMI < 25 kg/m2 in the first pregnancy. A study limitation was the lack of data on the effects of obstetric interventions and neonatal resuscitation efforts. CONCLUSIONS Risks of birth-asphyxia-related outcomes increased with maternal weight gain between pregnancies. Preventing weight gain before and in between pregnancies may improve neonatal health.