Cannabis Exposure and Adverse Pregnancy Outcomes Related to Placental Function

Cannabis use is increasing among reproductive-age individuals and the risks associated with cannabis exposure during pregnancy remain uncertain. To evaluate the association between maternal cannabis use and adverse pregnancy outcomes known to be related to placental function. Ancillary analysis of nulliparous individuals treated at 8 US medical centers with stored urine samples and abstracted pregnancy outcome data available. Participants in the Nulliparous Pregnancy Outcomes Study: Monitoring Mothers-to-Be cohort were recruited from 2010 through 2013; the drug assays and analyses for this ancillary project were completed from June 2020 through April 2023. Cannabis exposure was ascertained by urine immunoassay for 11-nor-9-carboxy-Δ9-tetrahydrocannabinol using frozen stored urine samples from study visits during the pregnancy gestational age windows of 6 weeks and 0 days to 13 weeks and 6 days (visit 1); 16 weeks and 0 days to 21 weeks and 6 days (visit 2); and 22 weeks and 0 days to 29 weeks and 6 days (visit 3). Positive results were confirmed with liquid chromatography tandem mass spectrometry. The timing of cannabis exposure was defined as only during the first trimester or ongoing exposure beyond the first trimester. The dichotomous primary composite outcome included small-for-gestational-age birth, medically indicated preterm birth, stillbirth, or hypertensive disorders of pregnancy ascertained by medical record abstraction by trained perinatal research staff with adjudication of outcomes by site investigators. Of 10 038 participants, 9257 were eligible for this analysis. Of the 610 participants (6.6%) with cannabis use, 32.4% (n = 197) had cannabis exposure only during the first trimester and 67.6% (n = 413) had ongoing exposure beyond the first trimester. Cannabis exposure was associated with the primary composite outcome (25.9% in the cannabis exposure group vs 17.4% in the no exposure group; adjusted relative risk, 1.27 [95% CI, 1.07-1.49]) in the propensity score-weighted analyses after adjustment for sociodemographic characteristics, body mass index, medical comorbidities, and active nicotine use ascertained via urine cotinine assays. In a 3-category cannabis exposure model (no exposure, exposure only during the first trimester, or ongoing exposure), cannabis use during the first trimester only was not associated with the primary composite outcome; however, ongoing cannabis use was associated with the primary composite outcome (adjusted relativ