A meta-analysis of 23 studies found a modest overall association between prenatal cannabis and birth defects (pooled OR 1.33), but most associations disappeared after adjustment, except for Ebstein anomaly and gastroschisis.
Obstetricians, teratology researchers, prenatal counselors
Most birth defect associations attenuated to non-significance after adjustment for confounders
What the researchers found
Across 23 studies spanning birth years 1968-2021, the pooled unadjusted odds ratio for any birth defect was 1.33 (95% CI 1.14-1.56), attenuating to 1.22 (95% CI 1.00-1.50) after adjustment. Most anatomic-group associations attenuated to non-significance after adjustment. Two specific defects retained significant adjusted associations: Ebstein anomaly (aOR 2.19, 95% CI 1.25-3.82) and gastroschisis (aOR 2.50, 95% CI 1.09-5.74), though both had limited supporting data.
Why it matters
This is the most comprehensive meta-analysis to date on cannabis and birth defects. The finding that most associations disappear after adjustment suggests confounding (tobacco, alcohol, socioeconomic factors) drives much of the apparent risk.
The numbers in context
23 studies; birth years 1968-2021; pooled OR 1.33 (95% CI 1.14-1.56); pooled aOR 1.22 (95% CI 1.00-1.50); Ebstein anomaly aOR 2.19 (95% CI 1.25-3.82); gastroschisis aOR 2.50 (95% CI 1.09-5.74)
How the study worked
Systematic review and meta-analysis searching Google Scholar, BIOSIS, PubMed/MEDLINE, EMBASE, CINAHL, and ClinicalTrials.gov. Screened with Abstrackr software. Included 23 observational studies examining birth defects with prenatal cannabis exposure. Meta-analyzed by anatomic group. Registered with PROSPERO.
What this study cannot tell us
Most included studies used unadjusted estimates and scored low on risk-of-bias assessment. Studies were heterogeneous in design and cannabis exposure measurement. The two specific defects with persistent associations had very limited data (2 and 5 studies respectively).
How to read the evidence
Registered systematic review and meta-analysis of 23 studies, but limited by poor quality of underlying studies and heavy reliance on unadjusted estimates.
When this study was published
Published 2023 analyzing studies from 1968-2021
The bigger picture
The inconsistency in this evidence base reflects the fundamental challenge of studying prenatal cannabis exposure: heavy confounding, self-reported use, and the impossibility of conducting randomized trials.
Questions still open
- Are the Ebstein anomaly and gastroschisis signals real or artifacts of limited data? Would studies with better confounding control and validated exposure assessment change the overall picture?
Common questions
Does cannabis use during pregnancy cause birth defects?
How strong is the evidence on cannabis and birth defects?
Read the original research
Prenatal Exposure to Cannabis and Risk of Major Structural Birth Defects: A Systematic Review and Meta-analysis.
Obstetrics and gynecology, 142(2), 269-283
Citation
Delker, Erin; Hayes, Shana; Kelly, Ann E; Jones, Kenneth L; Chambers, Christina; Bandoli, Gretchen. (2023). Prenatal Exposure to Cannabis and Risk of Major Structural Birth Defects: A Systematic Review and Meta-analysis.. Obstetrics and gynecology, 142(2), 269-283. https://doi.org/10.1097/AOG.0000000000005252
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