Abstract
Objective The aim of this study is to estimate the association between marijuana use during
pregnancy and total, spontaneous and indicated preterm birth.
Study Design Prospective cohort study of women receiving antenatal care at The Ohio State University
from 2010 to 2015. Marijuana use was assessed by questionnaire, record abstraction,
and urine toxicology. Women were followed through the end of pregnancy. Relative risks
were assessed with Poisson regression and time to delivery with proportional hazard
models.
Results Of 363 eligible women, 119 (33%) used marijuana in pregnancy by at least one measure.
In this high-risk cohort, preterm birth occurred to 36.0% of users and 34.6% of nonusers
(p = 0.81). The unadjusted relative risk of all preterm birth was 1.06 (95% confidence
interval [CI]: 0.76–1.47); the adjusted relative risk was similar 1.04 (95% CI: 0.72–1.50).
Spontaneous preterm birth was nonsignificantly elevated among users before 1.32 (95%
CI: 0.89–1.96), and after 1.21 (95% CI: 0.76–1.94) adjustment. Indicated preterm birth
was nonsignificantly reduced before 0.52 (95% CI: 0.22–1.23) and after 0.75 (95% CI:
0.29–2.15) adjustment. The unadjusted hazard ratio (HR) for time to preterm birth
was 1.26 (95% CI: 0.84–2.00); the adjusted HR was 1.32 (95% CI: 0.80–2.07). Both unadjusted
1.77 (95% CI: 1.06–2.93) and adjusted 2.16 (95% CI: 1.16–4.02) HRs for spontaneous
preterm birth were significantly elevated, primarily due to an increased risk of spontaneous
birth <28 weeks among users. The unadjusted and adjusted HRs for time to indicated
preterm birth were 0.69 (95% CI: 0.33–1.43) and 0.58 (95% CI: 0.23–1.46).
Conclusion Marijuana use was not associated with total preterm birth in this cohort, suggesting
that among women already at high risk of preterm birth, marijuana does not increase
risk further. However, there was a suggestion that pregnant women who use marijuana
may deliver earlier, particularly from spontaneous preterm birth, than women who do
not use marijuana.
Key Points
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Marijuana was not associated with risk of all preterm birth.
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Marijuana was not associated with reduced time to delivery.
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However, users had reduced time to spontaneous preterm birth.
Keywords
marijuana - cannabis - substance use - pregnancy - preterm birth
