Cannabis Use During the Pre-Conception Period and Pregnancy After Legalization

There is limited evidence of the impact of cannabis legalization on the prevalence of cannabis use and use of other substances. The aim of this exploratory observational study was to compare rates of cannabis use, cigarette smoking, alcohol consumption, and the use of any street drugs during the preconception period and in pregnancy in two convenience samples of pregnant persons in British Columbia, Canada, before and after the legalization of cannabis.

Any pregnant person residing in British Columbia, aged >19 years, at any gestational age was eligible to participate. Pre- and post-legalization study participants were recruited between May and October 2018 and July 2019 and May 2020, respectively. Multivariate models were constructed to examine the effect of legalization on cigarette smoking and the use of cannabis, alcohol, and street drugs, adjusting for demographic, pre-pregnancy, and pregnancy confounders.

From pre- to post-legalization, the prevalence of self-reported cannabis use during the preconception period increased significantly, from 11.74% (95% CI 9.19%–14.88%) to 19.38% (95% CI 15.45%–24.03%). Rates of cannabis use during pregnancy also increased from 3.64% (95% CI 2.32%–5.69%) before legalization to 4.62% (95% CI 2.82%–7.47%) after; however, this difference was not statistically significant. Adjusting for potential confounders, the post-legalization group had significantly higher odds of cannabis use during the preconception period (adjusted odds ratio 1.71; 95% CI 1.14–2.58) but not during pregnancy (adjusted odds ratio 1.66; 95% CI 0.75–3.65). Legalization was also not associated with significant changes in cigarette smoking, alcohol consumption, or the use of street drugs during the preconception period and pregnancy, after adjusting for potential confounders.

The preliminary evidence presented in this study shows that the legalization of cannabis was associated with 71% higher odds of cannabis use during the preconception period. Studies examining the effects of cannabis use on perinatal outcomes, as well as public health interventions and educational programs related to cannabis use, should include the preconception period as an area of focus.