Prenatal Cannabis Linked to Lower Birth Weight But Not Shorter Pregnancies Across Human and Animal Studies

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.

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.

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 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.

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.