Corsi DJ, et al. - Via a retrospective cohort study that included 661,617 pregnancies and 9,427 reported cannabis users, the researchers intended to evaluate the associations between self-reported prenatal cannabis use and adverse maternal and perinatal outcomes. Between cannabis users, imbalance in measured maternal obstetrical and sociodemographic characteristics was attenuated, generating a sample of 5,639 reported users and 92,873 nonusers. Significant association of cannabis users with greater frequency of small gestational age, placental abruption, need for transfer to neonatal intensive care and 5-minute Apgar score less than 4 was observed. Hence, an increased risk of preterm birth was notably related to cannabis use among pregnant women in Ontario, Canada. However, findings might be restricted by residual confounding.