Maternal body mass index in early pregnancy and severe asphyxia-related complications in preterm infants

Background: Little is known about the associations between maternal body mass index (BMI) and asphyxia-related morbidity in preterm infants (<37 weeks). We aimed to investigate associations between maternal BMI in early pregnancy and severe asphyxia-related neonatal complications in preterm infants (<37 weeks) and to examine whether possible associations were mediated by overweight- or obesity-related complications.

Methods: In this Swedish population-based cohort of 62 499 singleton non-malformed preterm infants born from 1997 to 2011, risks of low Apgar scores (0-3) at 5 and 10 minutes, neonatal seizures and intraventricular haemorrhage (IVH) were estimated through two analytical approaches. In the conventional approach, the denominator for risk was all live births at a given gestational age. In the fetuses-at-risk (FAR) approach, the denominator for risk was ongoing pregnancies at a given gestational age.

Results: Using the conventional approach, adjusted risk ratios per 10-unit BMI increase were 1.32 [95% confidence interval (CI) 1.13-1.54] and 1.37 (95% CI 1.12-1.67) for low Apgar scores at 5 and 10 minutes, respectively; 1.28 (95% CI 1.00-1.65) for neonatal seizures; and 1.18 (95% CI 1.01-1.37) for IVH. Using the FAR approach, corresponding risks were higher. These associations varied by gestational age (<32 and 32-36 weeks). Associations between maternal BMI and asphyxia-related outcomes were partly mediated through lower gestational age.

Conclusions: Increasing maternal BMI in early pregnancy is associated with increased risks of severe asphyxia-related complications in preterm infants. Our findings add to the evidence to support interventions to reduce obesity in woman of reproductive age.

Keywords: Maternal body mass index; nationwide cohort study; preterm morbidity.