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Is there an association between prenatal cannabis exposure and maternal, perinatal, and neonatal outcomes?
In this retrospective cohort study that included 661 617 pregnancies and 9427 reported cannabis users, the rate of preterm birth among reported cannabis users was 12% vs 6% in nonusers, a statistically significant difference.
Reported cannabis use in pregnancy was associated with significant increases in the rate of preterm birth following adjustment for confounding.
Recent evidence suggests that cannabis use during pregnancy is increasing, although population-based data about perinatal outcomes following in utero exposure remain limited.
To assess whether there are associations between self-reported prenatal cannabis use and adverse maternal and perinatal outcomes.
Design, Setting, and Participants
Population-based retrospective cohort study covering live births and stillbirths among women aged 15 years and older in Ontario, Canada, between April 2012 and December 2017.
Self-reported cannabis exposure in pregnancy was ascertained through routine perinatal care.
Main Outcomes and Measures
The primary outcome was preterm birth before 37 weeks’ gestation. Indicators were defined for birth occurring at 34 to 36 6/7 weeks’ gestation (late preterm), 32 to 33 6/7 weeks’ gestation, 28 to 31 6/7 weeks’ gestation, and less than 28 weeks’ gestation (very preterm birth). Ten secondary outcomes were examined including small for gestational age, placental abruption, transfer to neonatal intensive care, and 5-minute Apgar score. Coarsened exact matching techniques and Poisson regression models were used to estimate the risk difference (RD) and relative risk (RR) of outcomes associated with cannabis exposure and control for confounding.
In a cohort of 661 617 women, the mean gestational age was 39.3 weeks and 51% of infants were male. Mothers had a mean age of 30.4 years and 9427 (1.4%) reported cannabis use during pregnancy. Imbalance in measured maternal obstetrical and sociodemographic characteristics between reported cannabis users and nonusers was attenuated using matching, yielding a sample of 5639 reported users and 92 873 nonusers. The crude rate of preterm birth less than 37 weeks’ gestation was 6.1% among women who did not report cannabis use and 12.0% among those reporting use in the unmatched cohort (RD, 5.88% [95% CI, 5.22%-6.54%]). In the matched cohort, reported cannabis exposure was significantly associated with an RD of 2.98% (95% CI, 2.63%-3.34%) and an RR of 1.41 (95% CI, 1.36-1.47) for preterm birth. Compared with no reported use, cannabis exposure was significantly associated with greater frequency of small for gestational age (third percentile, 6.1% vs 4.0%; RR, 1.53 [95% CI, 1.45-1.61]), placental abruption (1.6% vs 0.9%; RR, 1.72 [95% CI, 1.54-1.92]), transfer to neonatal intensive care (19.3% vs 13.8%; RR, 1.40 [95% CI, 1.36-1.44]), and 5-minute Apgar score less than 4 (1.1% vs 0.9%; RR, 1.28 [95% CI, 1.13-1.45]).
Conclusions and Relevance
Among pregnant women in Ontario, Canada, reported cannabis use was significantly associated with an increased risk of preterm birth. Findings may be limited by residual confounding.
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Corresponding Author: Daniel J. Corsi, PhD, OMNI Research Group, Centre for Practice Changing Research, Ottawa Hospital Research Institute, L1242, 501 Smyth Rd, PO Box 241, Ottawa, ON K1H 8L6, Canada (firstname.lastname@example.org).
Accepted for Publication: June 3, 2019.
Published Online: June 18, 2019. doi:10.1001/jama.2019.8734
Author Contributions: Dr Corsi had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.
Concept and design: Corsi, Hsu, El-Chaar, Fell, Walker.
Acquisition, analysis, or interpretation of data: Corsi, Walsh, Weiss, Hawken, Fell, Walker.
Drafting of the manuscript: Corsi, Hsu, Fell, Walker.
Critical revision of the manuscript for important intellectual content: Corsi, Walsh, Weiss, El-Chaar, Hawken, Fell, Walker.
Statistical analysis: Corsi, Walsh, Weiss, Hawken, Fell.
Obtained funding: Hsu, El-Chaar.
Administrative, technical, or material support: Hsu, El-Chaar, Walker.
Supervision: Corsi, Walker.
Conflict of Interest Disclosures: Drs Corsi, El-Chaar, Hsu, and Walker reported receiving grants from the Canadian Institutes of Health Research. No other disclosures were reported.
Funding/Support: This study was funded by the Canadian Institutes of Health Research.
Role of the Funder/Sponsor: The funding source had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; and the decision to submit the manuscript for publication.
Data Sharing Statement: Requests for data access can be made to BORN Ontario at http://datadictionary.bornontario.ca/data-requests/.
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