Maternal asthma during pregnancy and extremes of body mass index increase the risk of perinatal mortality: a retrospective cohort study

Abstract

Objective: Asthma during pregnancy and extremes of body mass index (BMI) are independently associated with adverse pregnancy outcomes but the impact of the two conditions combined are currently unknown. The aim of this study was to determine the contribution of maternal BMI to adverse birth outcomes in pregnancies complicated by asthma.

Methods: The study utilized the routinely collected perinatal data on births at the Mater Mother's Hospital Brisbane, Australia, from January 2008 to December 2019. BMI was grouped as underweight (<18.5), normal weight (18.5-<24.99), overweight (25-29.99), and obese (≥30) and the population split by the presence and absence of maternal asthma. The comparison group was normal BMI, non-asthmatic pregnant women. A modified Poisson regression with robust variance was used to estimate the relative risk.

Results: In a retrospective cohort study of 110,057 pregnant women, 17.08% of women had asthma. Asthma and BMI were associated with an increased risk of poor fetal and neonatal outcomes. Asthma significantly increased the risk of stillbirth in underweight [adjusted RR: 2.22 (95% CI: 1.25-3.94] and obese [1.74 (1.11-2.71)]; neonatal death in underweight [3.41 (1.89-6.16)] and obese [2.22 (1.37-3.59)] and perinatal death in underweight [2.34 (1.50-3.66)] and obese [1.92 (1.38-2.67)] women. Admission to the neonatal intensive care unit was increased in neonates of underweight [1.65 (1.44-1.89)] and obese [1.26 (1.14-1.40)] asthmatic women.

Conclusions: Extremes of BMI, specifically underweight and obesity, increased the risk of adverse perinatal outcomes among asthmatic women highlighting the importance of accounting for BMI during pre-conception and pregnancy related management of asthmatic women.