A systematic review of 57 studies found prenatal cannabis exposure was consistently linked to lower birth weight in both humans and rodents, but not to shorter gestation or increased mortality.
Pregnant individuals, prenatal care providers, researchers studying fetal development effects of cannabis.
57 studies: lower birth weight in humans and rodents
What the researchers found
Among 21 rodent and 36 human studies, prenatal cannabis/THC exposure was significantly associated with lower birth weight in both species. It was not associated with gestational age in either species. In rodent studies, exposure did not affect mortality or litter size. In human studies, there was a tendency for exposed infants to have worse health indicators at delivery.
Why it matters
By combining human and animal evidence, this review strengthens the case that cannabis exposure reduces fetal growth. The consistency across species suggests a biological mechanism rather than purely socioeconomic confounding. However, the lack of effect on gestational age suggests cannabis affects growth rate rather than pregnancy duration.
The numbers in context
57 total studies (21 rodent, 36 human). Lower birth weight in both species. No effect on gestational age. No effect on rodent mortality or litter size. Tendency toward worse infant health at delivery in humans.
How the study worked
Systematic review following PRISMA guidelines across PubMed, CINAHL, and Scopus for human studies, and PubMed and Scopus for rodent studies. 21 rodent and 36 human studies were included after screening. Rodent outcomes: birth weight, litter size, mortality, gestation length. Human outcomes: birth weight, gestational age, infant health at delivery.
What this study cannot tell us
Heterogeneous study designs and exposure measurements across studies. Human studies cannot fully control for confounders (tobacco, alcohol, socioeconomic status). Rodent exposure protocols vary widely in dose, timing, and cannabinoid used. Mixed results for some outcomes may reflect true variability or methodological inconsistency.
How to read the evidence
Moderate: systematic methodology with cross-species consistency, though heterogeneous studies and inability to control all confounders in human studies.
When this study was published
2025 study
The bigger picture
The consistency of the birth weight finding across species and study designs is notable, but the mixed results for other outcomes and methodological differences between studies highlight how much is still unknown. As cannabis use in pregnancy increases with legalization, resolving these uncertainties becomes more urgent.
Questions still open
- What THC dose threshold affects birth weight? Are there critical windows during pregnancy when exposure is most harmful? Do the birth weight effects translate to long-term health consequences for offspring?
Common questions
Does cannabis during pregnancy affect the baby's size?
Does cannabis cause premature birth?
Read the original research
Risks of Cannabinoid Exposure on Birth Outcomes: A Systematic Review.
Cannabis and cannabinoid research, 10(5), 575-592
Citation
Reck, A Matthew; Reilly, Taylor; Vanegas, S Olivia; Shook, Natalie J; Kinsey, Steven G; Casavant, Sharon G. (2025). Risks of Cannabinoid Exposure on Birth Outcomes: A Systematic Review.. Cannabis and cannabinoid research, 10(5), 575-592. https://doi.org/10.1089/can.2025.0027
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