Key Points Question Is there an association between prenatal cannabis exposure and maternal, perinatal, and neonatal outcomes? Findings In this retrospective cohort study that included 661 617 pregnancies and 9427 reported cannabis users, the rate of preterm birth among reported cannabis users was 12% vs 6% in nonusers, a statistically significant difference. Meaning Reported cannabis use in pregnancy was associated with significant increases in the rate of preterm birth following adjustment for confounding. Abstract Importance Recent evidence suggests that cannabis use during pregnancy is increasing, although population-based data about perinatal outcomes following in utero exposure remain limited. Objective To assess whether there are associations between self-reported prenatal cannabis use and...