Trends in maternal body mass index, macrosomia and caesarean section in first-time mothers during the pandemic: a multicentre retrospective cohort study of 12 Melbourne public hospitals

Objective: To compare specific perinatal outcomes in nulliparas with a singleton infant in cephalic presentation at term, with and without exposure to the COVID-19 pandemic during pregnancy. We hypothesised that the pandemic conditions in Melbourne may have been an independent contributor to trends in maternal Body Mass Index ≥ 25 kg/m², macrosomia and caesarean section. Design: Multi-centre retrospective cohort study and interrupted time-series analysis. Setting: Metropolitan Melbourne, Victoria. Population: Singleton infants ≥ 20 weeks gestational age born between 1 January 2019 and 31 March 2022. Main outcome measures: Rates of maternal Body Mass Index ≥ 25 kg/m², macrosomia (birthweight ≥ 4000 g) and caesarean section. Results: 25 897 individuals gave birth for the first time to a singleton infant in cephalic presentation at term in the pre-pandemic cohort, and 25 298 in the pandemic-exposed cohort. Interrupted time-series analysis demonstrated no significant additional effect of the pandemic on pre-existing upward trends in maternal Body Mass Index ≥ 25 kg/m², caesarean section or macrosomia. The rate of maternal Body Mass Index ≥ 25 kg/m² was higher in the pandemic-exposed cohort compared with the pre-pandemic cohort, (45.82% vs. 44.58% respectively, p = 0.041) as was the overall rate of caesarean section (33.09% vs. 30.80%, p < 0.001). However, this increase in caesarean section was confined to individuals who had either an induction of labour or no labour. There was also a nonsignificant trend to higher rates of macrosomia in the pandemic-exposed cohort compared with the pre-pandemic cohort (8.55% vs. 7.99% respectively, p = 0.124). Conclusions: While rates of Body Mass Index ≥ 25 kg/m², pre-labour caesarean section, and caesarean section following induction of labour were higher among pandemic-exposed nulliparas, these findings represented a continuation of pre-existing upward trends, with no significant independent contribution from the pandemic. These trends are forecast to continue, with long term implications for population health.