Prenatal Cannabis Use Linked to Two Rare Abdominal Wall Birth Defects | Research

The takeaway

In a study of nearly 364,000 births, prenatal cannabis use was associated with a nearly 3-fold increased risk of omphalocele, a rare abdominal wall defect, but not with other major birth defects.

Pregnant individuals, healthcare providers, anyone interested in prenatal cannabis risks

2.92x increased risk of omphalocele with prenatal cannabis use

What the researchers found

Maternal prenatal cannabis use was associated with omphalocele (adjusted risk ratio 2.92) after propensity score adjustment. An initial association with gastroschisis did not survive full adjustment. No associations were found between prenatal cannabis use and any of the other 36 birth defects examined.

Why it matters

With prenatal cannabis use rising, understanding potential effects on fetal development is critical. This large study with universal screening (reducing detection bias) provides some of the strongest evidence to date on specific birth defect risks.

The numbers in context

363,952 infants studied. 6.2% (22,494) exposed to prenatal cannabis. Omphalocele risk ratio: 2.92 (95% CI: 1.26-6.77) after propensity score adjustment. Both conditions were rare: gastroschisis in 0.05% and omphalocele in 0.01% of births.

How the study worked

Population-based retrospective cohort of 363,952 singleton births from a health system that universally screens for substance use at prenatal care entry. Cannabis exposure was defined by self-report or positive toxicology. Researchers examined 38 specific birth defects across 8 organ systems using modified Poisson regression with propensity score adjustment.

What this study cannot tell us

Observational design cannot prove causation. Cannabis exposure was measured at prenatal care entry, not throughout pregnancy. Could not account for potency, frequency, or route of use. Very small number of omphalocele cases (n=48) limits precision.

How to read the evidence

Moderate: large population-based cohort with universal screening, but observational design and very small case numbers for the defects found

When this study was published

Published in 2025 using 2011-2020 birth data

The bigger picture

While the relative risk increase is notable, the absolute risk of omphalocele remains extremely low (0.01% of births). The lack of association with 36 other defects is also informative for risk counseling.

Questions still open

What biological mechanism might explain a specific link to abdominal wall defects? Does the timing or frequency of cannabis use during pregnancy matter?

Common questions

How common is omphalocele?

Very rare. In this study, omphalocele occurred in 0.01% of births (48 out of 363,952). Even with a roughly 3-fold increased relative risk from cannabis exposure, the absolute risk remains extremely low.

Were other birth defects affected?

No. The study examined 38 specific birth defects across 8 organ systems and found no association between prenatal cannabis use and any defect other than omphalocele (and a weaker signal for gastroschisis that didn't survive full statistical adjustment).

Read the original research

Maternal Prenatal Cannabis Use and Major Structural Birth Defects.

Birth defects research, 117(6), e2492

View on PubMed ↗Publisher’s paper ↗

Citation

Avalos, Lyndsay A; Adams, Sara R; Alexeeff, Stacey E; Oberman, Nina R; Does, Monique B; Steuerle, Kristin R; Ansley, Deborah R; Castellanos, Carley L; Padon, Alisa A; Silver, Lynn D; Young-Wolff, Kelly C. (2025). Maternal Prenatal Cannabis Use and Major Structural Birth Defects.. Birth defects research, 117(6), e2492. https://doi.org/10.1002/bdr2.2492