A cumulative meta-analysis of 27 studies spanning 36 years found that prenatal cannabis exposure increased preterm birth risk by 35%, with the finding now considered statistically stable.
Read this if you are pregnant or planning pregnancy and want to understand the evidence on cannabis and preterm birth.
aOR 1.3535% increased risk of preterm birth with prenatal cannabis exposure across 27 studies
What the researchers found
Pooling adjusted odds ratios from 27 observational studies (1986-2022), with sample sizes ranging from 304 to 4.83 million births, prenatal cannabis exposure was associated with an increased risk of preterm birth (pooled aOR = 1.35, 95% CI = 1.24-1.48). The cumulative meta-analysis approach showed that the estimate has stabilized over time — the stability threshold of 0.74 means a new study would need to find a very strong protective effect to shift the overall estimate to null.
Why it matters
This is one of the most comprehensive meta-analyses on prenatal cannabis and preterm birth. The cumulative approach demonstrates that the finding is not driven by a few studies and has become increasingly robust as evidence accumulates.
The numbers in context
- 27 observational studies included (1986-2022)
- Sample sizes: 304 to 4.83 million births
- Pooled aOR: 1.35 (95% CI: 1.24-1.48)
- Stability threshold: 0.74 (95% CI limit: 0.81)
- 35% increased risk of preterm birth
How the study worked
Cumulative meta-analysis following PRISMA guidelines. Searched PubMed, EMBASE, SCOPUS, PsychINFO, and Web of Science. Used Newcastle-Ottawa Scale for quality appraisal. Random-effects model with inverse variance weighting. Stability threshold analysis computed.
Who was studied
Pregnant women across 27 studies, sample sizes from 304 to 4.83 million births
What this study cannot tell us
All 27 studies were observational, so confounding cannot be fully eliminated. Cannabis use was mostly self-reported. Dose, frequency, and potency were not consistently captured. Co-use of tobacco (common among cannabis users) may confound results.
How to read the evidence
Cumulative meta-analysis of observational studies with stability analysis. Strong evidence synthesis despite limitations of underlying study designs.
When this study was published
Published in 2023. Covers the full body of evidence from 1986 to 2022.
The bigger picture
With cannabis use during pregnancy increasing as legalization expands, this stabilized meta-analytic evidence supports clear public health messaging: cannabis use during pregnancy is associated with a meaningful increase in preterm birth risk.
Questions still open
- Does the mode of cannabis consumption (smoking vs edibles) differentially affect preterm birth risk?
- Is the risk driven primarily by THC, or do other cannabinoids contribute?
- Does trimester of exposure modify the preterm birth risk?
Read the original research
The effect of prenatal cannabis exposure on offspring preterm birth: a cumulative meta-analysis.
Addiction (Abingdon, England), 118(4), 607-619
Citation
Duko, Bereket; Dachew, Berihun Assefa; Pereira, Gavin; Alati, Rosa. (2023). The effect of prenatal cannabis exposure on offspring preterm birth: a cumulative meta-analysis.. Addiction (Abingdon, England), 118(4), 607-619. https://doi.org/10.1111/add.16072