Prenatal cannabis use was associated with a 75% increase in the odds of low birth weight, even after adjusting for tobacco use, according to a recent meta-analysis.

In their systematic review, the researchers evaluated the association between prenatal cannabis use and adverse neonatal outcomes. The study, published in JAMA Pediatrics, synthesized data from 51 observational studies that included more than 21 million pregnancies to assess risks of low birth weight (LBW), preterm birth (PTB), small for gestational age (SGA), and perinatal mortality.

Led by Jamie O. Lo, MD, of the Department of Obstetrics and Gynecology at Oregon Health and Science University in Portland, the researchers conducted a comprehensive literature search across MEDLINE, CINAHL, PsycInfo, Global Health, and the Cochrane Database from November 1, 2021 through April 4, 2024. Eligible studies included cohort or case-control designs that compared pregnancies with and without cannabis exposure and adjusted for relevant confounders, including tobacco use. Data was pooled using random-effects meta-analyses, and certainty of evidence was evaluated using the Grading of Recommendations Assessment, Development, and Evaluation approach.

In adjusted analyses from 20 studies that included more than one million pregnancies, prenatal cannabis use was associated with 75% greater odds of LBW. A sensitivity analysis restricted to five studies of heavy cannabis use showed 136% higher odds.

Data from 20 adjusted studies with over 20 million pregnancies indicated a 52% increase in odds of PTB, which rose to 95% among heavy users.

Twelve studies that included more than 4.5 million pregnancies reported a 57% increase in odds of SGA among cannabis-exposed pregnancies. Sensitivity analysis of heavy use showed a 63% increase.

Six studies involving nearly 17 million pregnancies showed 29% higher odds of perinatal mortality with prenatal cannabis exposure. However, among heavy users, this association was not statistically significant.

The researchers concluded that prenatal cannabis use was independently associated with increased risks of LBW, PTB, and SGA with moderate certainty of evidence. These findings provide updated and more robust evidence that is supported by dose-response relationships and larger sample sizes, compared with prior reviews.

The authors noted the relevance of these findings for clinical counseling and public health strategies, particularly given the increasing prevalence of cannabis use during pregnancy. They concluded, "as prenatal cannabis use is a modifiable risk factor, clinical and public health efforts to reduce it have the potential to mitigate pregnancy and offspring morbidity and mortality."

The researchers reported no conflicts of interest.

Source: JAMA Pediatrics