A Prospective Study of Preconception and Early Pregnancy Cannabis Use and Birth Outcomes.

BACKGROUND

Cannabis use among reproductive-aged individuals is common, yet there are gaps in our understanding of the effect of cannabis use on adverse birth outcomes.

OBJECTIVE

To determine the extent to which female and male preconception cannabis use and female early pregnancy cannabis use are associated with the incidence of preterm birth (PTB), small-for-gestational-age birth (SGA), and large-for-gestational-age (LGA) birth.

METHODS

We analysed data from Pregnancy Study Online, an internet-based preconception cohort study of couples trying to conceive. Eligible participants were aged 21-45 years (female) and ≥ 21 years (male) and residents of the United States or Canada. We followed 6838 couples who conceived between June 2013 and September 2024. Both partners completed preconception baseline questionnaires; female participants completed preconception follow-up questionnaires every 8 weeks, at early (< 12 weeks) and late pregnancy (~32 weeks), and at 6 months postpartum. Participants self-reported cannabis use during preconception (female and male) and early pregnancy (female only). We ascertained birthweight and gestational age from birth certificates and questionnaires and defined PTB (delivery < 37 gestational weeks) and SGA and LGA (< 10th and > 90th percentiles of birthweight, respectively, for gestational age and sex). We fit Cox regression models to estimate hazard ratios (HR) and 95% confidence intervals (CI), adjusting for potential confounders.

RESULTS

Preconception cannabis use was not appreciably associated with PTB (≥ 1 per week vs. non-use: HR 1.06, 95% CI 0.71, 1.57 for females and HR 1.41, 95% CI 0.73, 2.75 for males). Higher frequency of female cannabis use in early pregnancy was associated with an increased incidence of PTB, although results were imprecise (≥ 1 per week vs. non-use: HR 1.87, 95% CI 1.06, 3.29; < 1/week vs. non-use: HR 0.85, 95% CI 0.36, 2.02). Cannabis use in either partner was not associated with the incidence of SGA or LGA.

CONCLUSIONS

Our results support the existing evidence that cannabis use during early pregnancy is a risk factor for PTB.