Effect of intrauterine marijuana exposure on fetal growth patterns and placental vascular resistance

Objective: The recent legalization of marijuana has increased overall use, including in pregnancy. Studies have previously associated marijuana use with adverse fetal neurodevelopmental outcomes. We sought to compare fetal sonographic growth parameters and placental perfusion, as measured by umbilical artery Dopplers, in women using daily marijuana versus nonusers. Methods: A retrospective cohort study capturing self–identified pregnant daily marijuana users with gestational aged matched controls was performed. We compared maternal demographics, fetal biometry, nuchal translucency, and umbilical artery Dopplers in marijuana users versus controls. Intrauterine growth restriction was defined as an estimated fetal weight <10th %. Results: In 55 first trimester ultrasounds, there were no differences in crown rump lengths or nuchal translucencies between the groups. Likewise, in 195-second trimester ultrasounds, no differences were noted in biometry. Second trimester umbilical artery systolic to diastolic ratios were higher in marijuana users compared to nonusers (4.02 versus 3.92, p =.024). In the third trimester, 26 of 192 marijuana exposed fetuses were growth restricted compared to 6 of 192 controls (p =.002), and umbilical artery systolic to diastolic ratios were higher (3.52 versus 3.12, p =.0001). Four cases of absent and reversed end diastolic flow were observed in marijuana users, while no cases were observed in controls. Conclusions: Our data shows that daily marijuana use is associated with impaired fetal growth and increased placental vascular resistance. Marijuana consumption in pregnancy should be avoided until further studies delineate its exact potential for fetotoxicity.