Prenatal Cannabis Use is Associated with Pre-Term Birth and Other Adverse Outcomes

Cannabis use among women of childbearing age is common, and many continue use while pregnant. With recent legalization in Canada and parts of the US, cannabis use during pregnancy will likely become more common. Researchers investigated whether self-reported prenatal cannabis use was associated with pre-term birth (<37 weeks) and 10 other maternal, perinatal, and neonatal outcomes among pregnant women in the BORN Ontario database between 2012 and 2017. To address confounding in this retrospective cohort study, they matched pregnant women who used cannabis with pregnant women who did not. Participants and controls were matched on age, parity, income, smoking status, alcohol use, opioid use, selective serotonin reuptake inhibitor use, other drug use, maternal mental health conditions, antenatal care, and year of birth.

• Overall, 661,617 of 759,281 (87%) pregnant women had sufficient data to be included. The mean age was 30 years, and 9427 (1.4%) reported cannabis use.
• In the matched cohort, self-reported cannabis use was associated with increased risk of preterm birth at <37 weeks (relative risk (RR), 1.41), small for gestational age (RR, 1.53), placental abruption (RR, 1.72), stillbirth (RR, 1.25), transfer to the neonatal intensive care unit (RR, 1.40), and Apgar score <4 (RR, 1.28).
• Cannabis use was associated with a reduced risk of pre-eclampsia (RR, 0.90) and gestational diabetes (RR, 0.91).

Comments: Despite the matched analysis, residual confounding may have biased these results. Furthermore, the study does not explore the importance of the timing or amount of prenatal cannabis use. Regardless, women should be advised that cannabis use during pregnancy may be associated with adverse peri- and neonatal outcomes.

Miriam Harris, MD† and Alexander Y. Walley, MD, MSc

† Contributing editorial intern and Addiction Medicine Fellow, Boston Medical Center/Boston University School of Medicine

Reference: Corsi DJ, Walsh L, Weiss D, et al. Association between self-reported prenatal cannabis use and maternal, perinatal, and neonatal outcomes. JAMA. 2019;322(2):145–152.