Marijuana Use in Pregnancy and Its Effects on Birth Weight and Gestational Age at Delivery [17R

Abstract

INTRODUCTION: Prior studies have suggested that marijuana exposure may affect the growth of the fetus and the ultimate birth weight of an infant but have been inconsistent in their methodologies and have shown conflicting results. This study aims to clarify any association between marijuana use and pregnancy outcomes. METHODS: A retrospective chart review of electronic medical records for singleton births from September 2013 through January 2015 with available urine drug screens (UDS) at initiation of prenatal care and delivery was conducted. Patients who used drugs other than marijuana were excluded. Patients were grouped into no positive UDS, positive UDS for only tetrahydrocannabinol (THC) at presentation, positive UDS for only THC at delivery, and positive UDS for only THC at both initial presentation and delivery. RESULTS: The incidence of marijuana use in pregnancy exclusive of other drugs as evidenced by only tetrahydrocannabinol in the urine of 2173 patients was 22.5%. Infants born to mothers who tested positive at both times during pregnancy were of lower birth weight compared to non-users [2925 gm (IQR 2522-3265) versus 3235 gm (IQR: 2900-3591), P = < 0.001]. This effect cannot be explained by earlier gestational age alone as persistent marijuana users only delivered two gestational days earlier than non-users (39 vs 39.3 weeks). Concomitant tobacco use during pregnancy was not noted to impact infant birth weight using the ANCOVA. CONCLUSION: Marijuana use is negatively correlated with fetal birth weight and length at birth. Additional patient education and cessation interventions should be explored.