Now before we talk about marijuana use in pregnancy and autism, let’s review some stuff we already know about MJ use in pregnancy. First it does cross the placenta. THC crosses the placenta and can be found in fetal circulation at 10% of the maternal level. Second, we also know that marijuana can bind to fetal cannabinoid receptors as early as 14 weeks of pregnancy. Third, studies have shown that exposure to marijuana in pregnancy can disrupt normal brain development. Children born to women who used marijuana while pregnant are more likely to have low birth weight at birth, hyperactivity, and attention, cognitive and behavioral issues.
So, a couple weeks ago a study out of Canada published in Nature showed that women who used marijuana while pregnant were 1.5 times more likely to have a child with autism. The researchers reviewed 500,000 births between 2007 and 2012 in Ontario, Canada. They found an association between maternal cannabis use in pregnancy and the incidence of autism spectrum disorder in these children. The incidence of autism spectrum disorder diagnosis was 4 per 1000 children who were exposed to marijuana and 2.4 among children who were not exposed to MJ in utero.
So, while this study does not definitively prove that marijuana use during pregnancy causes autism, there does seem to be a strong association. Based on these findings, as well as ACOG (American College of Obstetricians and Gynecologists) recommendation, we encourage our patients to avoid using marijuana during pregnancy and breastfeeding.