Cannabis Use in Pregnancy in British Columbia and Selected Birth Outcomes.

OBJECTIVE: This study sought to determine the association between cannabis use in pregnancy and stillbirth, small for gestational age (SGA) (<10th percentile), and spontaneous preterm birth (<37 weeks). METHODS: The study used abstracted obstetrical and neonatal medical records for deliveries in British Columbia from April 1, 2008 to March 31, 2016 that were contained in the Perinatal Data Registry of Perinatal Services British Columbia. Chi-square tests were conducted to compare maternal sociodemographic characteristics by cannabis use. Logistic regression was conducted to determine the association between cannabis use and SGA and spontaneous preterm births. Cox proportional hazards regression modelling was used to identify the association between cannabis use and stillbirth. Secondary analyses were conducted to ascertain differences by timing of stillbirth (Canadian Task Force Classification II-2). RESULTS: Maternal cannabis use has increased in British Columbia over the past decade. Pregnant women who use cannabis are younger and more likely to use alcohol, tobacco, and illicit substances and to have a history of mental illness. Using cannabis in pregnancy was associated with a 47% increased risk of SGA (adjusted OR 1.47; 95% CI 1.33-1.61), a 27% increased risk of spontaneous preterm birth (adjusted OR 1.27; 95% CI 1.14-1.42), and a 184% increased risk of intrapartum stillbirth (adjusted HR [aHR] 2.84; 95% CI 1.18-6.82). The association between cannabis use in pregnancy and overall stillbirth and antepartum stillbirth did not reach statistical significance, but it had comparable point estimates to other outcomes (aHR 1.38; 95% CI 0.95-1.99 and aHR 1.34; 95% CI 0.88-2.06, respectively). CONCLUSION: Cannabis use in pregnancy is associated with SGA, spontaneous preterm birth, and intrapartum stillbirth.