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Chemical products from marijuana use are transferred across the placenta and into breast milk. In rat models, fetal plasma levels were approximately 10 percent of maternal levels after acute exposure to delta-9-tetrahydrocannabinol (THC), the primary psychoactive cannabinoid. However, repetitive exposure of THC resulted in higher fetal levels. While there is no high-quality evidence to suggest an increase in congenital anomalies among marijuana users, the findings from available studies are limited by relatively small numbers of women whose used only cannabis and confounders, such as lower supplemental folic acid intake among users. Mixed results have also been reported regarding pregnancy outcomes such as low birth weight, preterm birth, and stillbirth in marijuana users. Better cohort studies that corrected for maternal confounders such as socioeconomic status, maternal weight, tobacco use, and alcohol consumption have reported an association between cannabis use and low birth weight, preterm birth, small for gestational age, and admission to a neonatal intensive care unit. Despite conflicting data, concerning trends suggest a negative impact on pregnancy outcomes in women who use marijuana. Therefore the American College of Obstetricians and Gynecologists (ACOG) discourages marijuana use during pregnancy.