Systematic review finds mixed evidence on whether cannabis in pregnancy causes birth defects | Research

The takeaway

A systematic review of 20 studies found mixed results for associations between prenatal cannabis exposure and structural birth defects, with too little research on most organ systems to draw conclusions.

OB/GYN providers, reproductive epidemiologists, and pregnant individuals seeking evidence on cannabis safety.

Only 12 of 20 studies adjusted for confounders; findings mixed across organ systems

What the researchers found

For the most-studied defect types (cardiac, gastrointestinal, CNS), findings were mixed across studies. For less-studied defect types (orofacial, eye, genitourinary, musculoskeletal), the sparse research mostly found no association, but sample sizes were too small for confidence.

Why it matters

Cannabis use during pregnancy is increasing, and pregnant people need clear information about risks. The current evidence on birth defects is too sparse and inconsistent to provide definitive guidance.

The numbers in context

20 articles identified, 12 with adjusted analyses included in interpretation. Seven organ systems examined: cardiac (4 studies), CNS (3), gastrointestinal (3), orofacial (2), eye (1), genitourinary (1), musculoskeletal (1).

How the study worked

Systematic review following PRISMA guidelines. Identified 20 articles, with analysis focused on 12 that adjusted for potential confounders. Findings organized by seven organ systems.

What this study cannot tell us

Few studies per organ system make conclusions unreliable. Heterogeneous exposure definitions across studies. Most studies rely on self-reported cannabis use. Confounding by tobacco, alcohol, and other substance co-use is difficult to fully address.

How to read the evidence

Systematic review with rigorous methodology, but limited by the sparse and inconsistent underlying evidence base.

When this study was published

Published 2023.

The bigger picture

Most research on cannabis in pregnancy has focused on low birth weight and preterm birth. Structural birth defects have received far less attention, leaving a significant gap in reproductive safety data.

Questions still open

Would studies using biomarker-verified cannabis exposure produce different results? Are there critical windows during organogenesis when cannabis exposure poses the greatest risk?

Common questions

Does cannabis cause birth defects?

The evidence is insufficient to answer definitively. This systematic review found mixed results for the most-studied defect types (heart, brain, gastrointestinal) and too little research on others. The absence of a clear association does not mean cannabis is safe during pregnancy.

Why is the evidence so limited?

Studying birth defects requires very large samples because individual defect types are rare. Most cannabis-pregnancy studies have focused on more common outcomes like birth weight. Additionally, accurately measuring cannabis exposure during pregnancy is difficult.

Read the original research

A systematic review of in utero cannabis exposure and risk for structural birth defects.

Frontiers in pediatrics, 11, 1149401

View on PubMed ↗Publisher’s paper ↗

Citation

Sujan, Ayesha C; Pal, Anish; Avalos, Lyndsay A; Young-Wolff, Kelly C. (2023). A systematic review of in utero cannabis exposure and risk for structural birth defects.. Frontiers in pediatrics, 11, 1149401. https://doi.org/10.3389/fped.2023.1149401