Maternal cannabis use during pregnancy and maternal and neonatal outcomes: A retrospective cohort study

Objective: To examine the relationship between reported prenatal cannabis use and neonatal and maternal outcomes and whether the legalisation of cannabis in Canada affected the rates of reported use or the association with maternal and neonatal outcomes. Design: Population-based retrospective cohort study. Setting: Routinely collected data in a real-world setting. Population: All women in the Canadian province of Nova Scotia with singleton births between 1 January 2004 and 30 June 2021. Methods: The association between cannabis use and maternal and neonatal outcomes was examined using generalised linear models with inverse probability weighting. Main outcome measures: Maternal and neonatal outcomes in the peripartum and postpartum period. Results: Rates of reported cannabis use in pregnancy increased from 1.3% to 7.5% over the study period with no appreciable change in slope after legalisation in 2018. Infants of mothers reporting cannabis use in pregnancy were more likely to have major anomalies and a 5-minute Apgar score <= 7, require neonatal intensive care unit admission, and had lower birthweight, head circumference and birth length than infants of mothers not reporting cannabis use. These associations did not differ before and after legalisation. Conclusions: Reported cannabis use during pregnancy is associated with early postnatal complications and reduced fetal growth, even after taking into account a range of confounding factors. Rates of reported cannabis use during pregnancy increased over the past 5 years in Nova Scotia with no apparent additional effect of legalisation.