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

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.

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.

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.

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.

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.