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.

Abstract 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 ≥25kg/m², macrosomia and caesarean section. Design: Multi-centre retrospective cohort study with 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 ≥25kg/m², macrosomia (birthweight >4000g) 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. Compared with the pre-pandemic cohort, the rate of maternal Body Mass Index ≥25kg/m² (45.82% vs 44.57%, p=0.005), the rate of caesarean section (33.09% vs 30.80%, p<0.001) and the rate macrosomia (8.55% vs 7.99%, p=0.1) were higher among 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 ≥25kg/m², caesarean section and macrosomia. Conclusions: Rates of Body Mass Index ≥25kg/m² and caesarean section among nulliparous individuals during pregnancy were higher following the pandemic in Melbourne. However, this appears to be 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.