Risks of Cannabinoid Exposure on Birth Outcomes: A Systematic Review

Introduction: With the changing legal landscape, the acceptance and availability of cannabis products have increased. Cannabis products are generally considered "natural" and relatively safe by consumers. However, growing empirical evidence from humans and other animals indicates that cannabis negatively affects human health. In contrast to the well-known teratogenic effects of alcohol and tobacco products, the safety of cannabis product use during pregnancy has not yet been established. The goal of this systematic review was to determine the patterns that exist in human and rodent literature on the effects of prenatal exposure to cannabis products and delta-9-tetrahydrocannabinol (THC) on birth outcomes. Methods: A systematic review of rodent and human studies was conducted using PRISMA guidelines. Rodent search strategy used PubMed and Scopus with terms "prenatal OR perinatal OR in utero OR maternal exposure AND cannabis OR THC or cannabinoids AND exposure NOT review NOT Human." Human search strategy used PubMed, CINAHL, and Scopus with terms "cannabinoids OR cannabis OR THC OR marijuana" AND "pregnancy OR pregnant OR prenatal AND "infant outcome OR infant health." After deleting duplicates and studies that did not fit the inclusion criteria, 21 rodent and 36 human studies were selected for review. Rodent studies focused on birth weight, litter size, mortality, and gestation length. Human studies have focused on birth weight, gestational age, and infant health at delivery. Results: In both human and rodent studies, prenatal exposure to cannabis was significantly associated with lower birth weight; however, it was not significantly associated with gestational age in rodents or humans. In most rodent studies, prenatal exposure to cannabis did not affect mortality or litter size. In human studies, there was a tendency for infants exposed to cannabis during pregnancy to have worse health at delivery. Findings indicate that cannabis exposure in utero may be associated with worse birth outcomes; however, the results are mixed and vary by species and outcome. Discussion: Methodological differences and scant existing research may have contributed to this inconsistency. Given the legalization of cannabis product use for recreational and medicinal purposes is growing, additional research is necessary to determine its influence on fetal and infant health outcomes.