Birth Outcomes of Neonates Exposed to Marijuana in Utero: A Systematic Review and Meta-analysis

IMPORTANCE: While some studies have found an association between marijuana use and adverse neonatal outcomes, results have not been consistent across all trials. OBJECTIVE: To assess available data on neonatal outcomes in marijuana-exposed pregnancies. DATA SOURCES: PubMed, Medline, ClinicalTrials.gov, Cochrane, Scopus, and Web of Science were searched from each database's inception until August 16, 2021. STUDY SELECTION: All interventional and observational studies that included pregnant women who were exposed to marijuana compared with pregnant women who were not exposed to marijuana and that reported neonatal outcomes were included. DATA EXTRACTION AND SYNTHESIS: Reporting followed the Preferred Reporting Items for Systematic Reviews and Meta-analyses guideline. Data were extracted by 2 authors for all outcomes, which were pooled using a random-effects model as mean difference or risk ratio (RR) and 95% CI. Data were analyzed from August through September 2021. MAIN OUTCOMES AND MEASURES: All outcomes were formulated prior to data collection. Outcomes included incidence of birth weight less than 2500 g, small for gestational age (defined as less than the fifth percentile fetal weight for gestational age), rate of preterm delivery (defined as before 37 weeks’ gestation), gestational age at time of delivery, birth weight, incidence of neonatal intensive care unit (NICU) admission, Apgar score at 1 minute, Apgar score at 5 minutes, incidence of an Apgar score less than 7 at 5 minutes, fetal head circumference, and fetal length. RESULTS: Among 16 studies including 59 138 patients, there were significant increases in 7 adverse neonatal outcomes among women who were exposed to marijuana during pregnancy vs those who were not exposed during pregnancy. These included increased risk of birth weight less than 2500 g (RR, 2.06 [95% CI, 1.25 to 3.42]; P = .005), small for gestational age (RR, 1.61 [95% CI, 1.44 to 1.79]; P < .001), preterm delivery (RR, 1.28 [95% CI, 1.16 to 1.42]; P < .001), and NICU admission (RR, 1.38 [95% CI, 1.18 to 1.62]; P < .001), along with decreased mean birth weight (mean difference, −112.30 [95% CI, −167.19 to −57.41] g; P < .001), Apgar score at 1 minute (mean difference, −0.26 [95% CI, −0.43 to −0.09]; P = .002), and infant head circumference (mean difference, −0.34 [95% CI, −0.63 to −0.06] cm; P = .02). CONCLUSIONS AND RELEVANCE: This study found that women exposed to marijuana in pregnancy were at a significantly increased risk of some adverse neonatal outcomes. These findings suggest that increasing awareness about these risks may be associated with improved outcomes.