The Impact of BMI and inter-pregnancy BMI change with birth outcomes in an Australian obstetric cohort: A retrospective cohort study.

The aim of this retrospective cohort study was to assess maternal and neonatal outcomes associated with increasing body mass index (BMI) and inter-pregnancy BMI changes in an Australian obstetric population from 2008 to 2013. BMI was available for 14,875 women categorised into groups according to: underweight (≤18 kg/m2 ); normal weight (19–24 kg/m2 ); overweight (25–29 kg/m2 ); obese class I (30–34 kg/m2 ); obese class II (35–39/kg2 ) and obese class III (40+ kg/m2 ). BMI categories and maternal, neonatal and birthing outcomes were examined using logistic regression. Inter-pregnancy changes in BMI and the risk of adverse outcomes in the subsequent pregnancy were also examined. In bivariate-adjusted models obese women were at an increased risk of caesarean section, gestational diabetes, hypertensive disorders of pregnancy and neonatal morbidities including macrosomia, hypoglycaemia, low 5-minute Apgar score and respiratory distress. Women, of all parities, who experienced an inter-pregnancy increase of ≥3 BMI units had a higher adjusted OR [CI] of the following: low 5-minute Apgar score 3.242 [1.557, 7.118]; gestational diabetes 3.258 [1.129, 10.665] and hypertensive disorders of pregnancy 3.922 [1.243, 14.760]. These women were more likely to give birth vaginally 2.030 [1.417, 2.913]. Conversely, women whose parity changed from 0 to 1 and experienced an inter-pregnancy increase of ≥3 BMI units had a higher adjusted OR [CI] of caesarean section in their second pregnancy 1.806 [1.139, 2.862]. Women who are overweight or obese have a significantly increased risk of various adverse maternal, neonatal and birthing outcomes. Inter-pregnancy weight gain, regardless of parity and baseline BMI, increases the risk of various adverse outcomes.