Cannabis Use in Pregnancy Linked to Preterm Birth, Low Birth Weight, and Small Babies Even After Accounting for Tobacco | Research

The takeaway

An updated meta-analysis of over 21 million pregnancies found moderate-certainty evidence that cannabis use during pregnancy increased odds of preterm birth, low birth weight, and small-for-gestational-age babies, even after adjusting for tobacco co-use.

Pregnant individuals, healthcare providers counseling pregnant patients, and policymakers addressing cannabis use during pregnancy.

Cannabis in pregnancy: 75% higher odds of low birth weight, 52% higher odds of preterm birth

What the researchers found

Cannabis use in pregnancy was associated with increased odds of low birth weight (OR=1.75), preterm birth (OR=1.52), small for gestational age (OR=1.57), and perinatal mortality (OR=1.29). The evidence certainty for the first three outcomes was upgraded to moderate from low/very low in the prior review. Critically, these associations held after adjusting for co-use of tobacco products.

Why it matters

This is one of the largest and most rigorous analyses of cannabis and pregnancy outcomes. The upgrade from low to moderate certainty evidence, combined with the enormous sample size, substantially strengthens the case that prenatal cannabis use carries real risks to newborns.

The numbers in context

51 studies, 21.1 million participants. Low birth weight: OR=1.75 (95% CI: 1.41-2.18, 20 studies). Preterm birth: OR=1.52 (95% CI: 1.26-1.83, 20 studies). Small for gestational age: OR=1.57 (95% CI: 1.36-1.81, 12 studies). Perinatal mortality: OR=1.29 (95% CI: 1.07-1.55, 6 studies, low certainty).

How the study worked

Updated living systematic review and meta-analysis published in JAMA Pediatrics. Added 8 new studies (1.7 million participants) to the prior review for a total of 51 studies (21.1 million participants). Random-effects meta-analyses of adjusted odds ratios. Evidence graded using GRADE approach.

What this study cannot tell us

Observational studies cannot fully eliminate confounding. Cannabis exposure is mostly self-reported. Different studies measured exposure at different points in pregnancy. Dose-response data is limited.

How to read the evidence

Strong: updated JAMA Pediatrics meta-analysis of 51 studies with 21 million participants, GRADE moderate certainty for primary outcomes, and adjustment for tobacco co-use.

When this study was published

2025 study with literature through April 2024.

The bigger picture

As cannabis use during pregnancy increases and perceived risk decreases, this upgraded evidence provides clinicians with stronger data for patient counseling. The fact that associations persist after tobacco adjustment addresses a major prior criticism.

Questions still open

Is there a dose threshold below which prenatal cannabis is safe? Do different consumption methods (smoking vs edibles) carry different risks? Are there critical windows during pregnancy when exposure is most harmful?

Common questions

Could tobacco use explain these findings instead of cannabis?

No. The meta-analysis specifically used studies that adjusted for tobacco co-use, and the associations with cannabis remained significant. This addresses a major prior criticism of earlier evidence.

How strong is this evidence compared to previous reviews?

The evidence was upgraded from low/very low certainty to moderate certainty in this update, reflecting both more studies and more consistent findings. This is published in JAMA Pediatrics, a top-tier journal.

Read the original research

Prenatal Cannabis Use and Neonatal Outcomes: A Systematic Review and Meta-Analysis.

JAMA pediatrics, 179(7), 738-46

View on PubMed ↗Publisher’s paper ↗

Citation

Lo, Jamie O; Ayers, Chelsea K; Yeddala, Snehapriya; Shaw, Beth; Robalino, Shannon; Ward, Rachel; Kansagara, Devan. (2025). Prenatal Cannabis Use and Neonatal Outcomes: A Systematic Review and Meta-Analysis.. JAMA pediatrics, 179(7), 738-46. https://doi.org/10.1001/jamapediatrics.2025.0689