High-Potency Prenatal Cannabis Exposure and Birth Outcome Measures

Background/Objectives: Pregnant women have limited information on the impact of prenatal cannabis exposure (PCE) alone. Our aim was to determine if PCE, without alcohol, tobacco, or illicit drug use, is associated with altered birth outcome measures in obstetrically low-risk women. Methods: In this observational cohort study, pregnant women were recruited between 2019 and 2022 from communities in Washington and Oregon, USA, and enrolled following their first trimester. PCE eligibility required a minimum of three days/week of cannabis use during the first trimester with no required minimum use thereafter. For all participants, illicit drug, nicotine, or alcohol use was exclusionary throughout pregnancy and monitored via urine toxicology at multiple time points. Cannabis use was quantified into delta-9-tetrahydrocannabinol (THC) and cannabidiol (CBD) mg/day using product weight and potency. Outcome measures included gestational age, weight, length, head circumference, and Apgar scores. Results: Study participants included 37 people in the PCE cohort and 35 controls. Average cannabis use for the PCE cohort was 198.0 mg of THC (SD = 221.2 mg)/day and 3.5 mg of CBD (SD = 4.3)/day. PCE newborns weighed less (38th vs. 52nd percentile, p = 0.04) and were shorter (40th vs. 55th percentile, p = 0.03) for their gestational age than controls. Female PCE newborns had smaller head circumference for gestational age (28th percentile; SD = 23), compared to male PCE newborns (55th percentile; SD = 32; p = 0.02). Conclusions: PCE is associated with reduced birth weight and shorter length for gestational age. The effect of PCE on brain growth may be sexually dimorphic. Future PCE studies should include sex as a biological variable and longitudinally evaluate long-term developmental and physiological outcomes.