EBM Focus: Antenatal Cannabis Use May Increase Risk of Preterm Delivery

Medical | Carina Brown| August 06, 2019

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A new study evaluated self-reported cannabis use in pregnancy and maternal, perinatal, and neonatal outcomes. Read more in the latest EBM Focus.

EBM Focus articles provide concise summaries of clinical trials most likely to inform clinical practice curated by the DynaMed® editorial team.

Cannabis use continues to rise among women of childbearing age, particularly as legal regulations become less restrictive and access to the substance in its various formulations increases. For clinicians, counseling patients about the potential risks and benefits of cannabis use is challenging, as robust research has not been conducted due to restrictive research policies. Although guidelines recommend against the use of marijuana in pregnancy, very few studies are available to support this recommendation.

When matched to non-users, cannabis users were more likely to have preterm delivery at all gestational ages.

A recent retrospective cohort study abstracted data from a large database in Ontario with information on pregnant women, including prenatal care information, obstetric complications, and birth outcomes. In a dataset of over 600,000 women from 2012 to 2017, 1.4 percent of women reported cannabis use. Cannabis users were more likely to be nulliparous and younger than non-users, and were also more likely to use tobacco and alcohol during pregnancy. When matched to non-users, cannabis users were more likely to have preterm delivery at all gestational ages, including less than 28 weeks (relative risk [RR] 1.97, 95% CI 1.70-2.28), had a higher rate of placental abruption (RR 1.72, 95% CI 1.54-1.92), and were more likely to require intensive care unit transfer (RR 1.40, 95% CI 1.36-1.44). There were also differences in the rates of small for gestational age infants (RR 1.41, 95% CI 1.36-1.45) and stillbirth (RR 1.25, 95% 1.05-1.48). In contrast, rates of preeclampsia (RR 0.90, 95% CI 0.86-0.95) and gestational diabetes (RR 0.91, 95% CI 0.86-0.96) were slightly reduced among cannabis users compared to non-users.  

Patients may consider using cannabis during pregnancy due to a perceived benefit for symptoms of nausea and vomiting, but may be hesitant to report use given the persistent social stigma. Prenatal care providers may also be hesitant to bring up this commonly used substance, particularly given the paucity of data regarding cannabis use in pregnancy. This study demonstrates that there may be an increased risk of adverse maternal and neonatal outcomes with maternal cannabis use. This data should empower clinicians to discuss the possible harms and unsubstantiated clinical benefits of prenatal cannabis use.

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Carina Brown

This EBM Focus was written by Carina Brown, MD, Assistant Professor at Cone Health Family Medicine Residency. Edited by Alan Ehrlich, MD, Executive Editor at DynaMed® and Associate Professor in Family Medicine at the University of Massachusetts Medical School and Katharine DeGeorge, MD, MS, Associate Professor in Family Medicine at the University of Virginia and Clinical Editor at DynaMed®.

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