Notes

What studies have shown more conclusively is that daily or weekly marijuana use may make your pregnancy more high-risk. For example, a 2011 Australian study of almost 25,000 women concluded that babies born to mothers who used marijuana were twice as likely to end up in the neonatal intensive care unit (NICU) compared to other babies. In addition, a review of 24 studies looking at marijuana use during pregnancy found that pot use during pregnancy makes baby 77 percent more likely to be underweight at birth. And an analysis of 12,069 women found that women who smoked pot at cigarettes during pregnancy were more likely to have babies with smaller heads and low birth weight than woman who just smoked cigarettes (though the risk was high for women who smoked cigarettes, as well).

What about long-term effects? A few studies have found that after 3 years of age, children born to marijuana-smoking mothers score slightly differently on cognitive and behavioral tests compared with other babies. A decade-long Canadian study found that at 4 years old, children born to mothers who used marijuana on a daily basis during pregnancy scored lower on memory tests, though there was no impact on overall intelligence scores. At age 10, kids had a slightly increased risk of hyperactivity, inattention and impulsivity.

Scientists who have turned to mice to understand the effects of THC on development showed in early 2014 that developing mice exposed to THC had altered connections between cells in their brain. They think this could explain why exposure to THC during pregnancy can leave children with lasting cognitive and memory changes.