NIDA director Nora Volkow commented on the study in an editorial published online in the Journal of the American Medical Association and it was picked up by major news outlets without any rebuttal, including Huffington Post, the Washington Post and USA Today (via AP).
Volkow writes, "Although the evidence for the effects of marijuana on human prenatal development is limited at this point, research does suggest that there is cause for concern. A recent review and meta-analysis found that infants of women who used marijuana during pregnancy were more likely to be anemic, have lower birth weight, and require placement in neonatal intensive care than infants of mothers who did not use marijuana. Studies have also shown links between prenatal marijuana exposure and impaired higher-order executive functions such as impulse control, visual memory, and attention during the school years."
Volkow cherry-picked studies to back up her assertions, citing a BMJ analysis that looked at 24 studies, and a 2011 NIDA-funded review from Texas Children's Hospital.
A glaring omission from Volkow's article was the recent study published in the journal Obstetrics & Gynecology, Maternal Marijuana Use and Adverse Neonatal Outcomes: A Systematic Review and Meta-analysis, which found that the moderate use of cannabis during pregnancy is not an independent risk factor for adverse neonatal outcomes such as low birth weight.
As NORML reported, in that study, investigators at the Washington University School of Medicine in St. Louis reviewed outcomes from more than two-dozen relevant case-control studies published between 1982 and 2015, and concluded: "[T]he results of this systematic review and meta-analysis suggest that the increased risk for adverse neonatal outcomes reported in women using marijuana in pregnancy is likely the result of coexisting use of tobacco and other cofounding factors and not attributable to marijuana use itself. Although these data do not imply that marijuana use during pregnancy should be encouraged or condoned, the lack of a significant association with adverse neonatal outcomes suggests that attention should be focused on aiding pregnant women with cessation of substances known to have adverse effects on the pregnancy such as tobacco."
Volkow does state, "One challenge is separating these effects from those of alcohol, tobacco, and other drugs, because many users of marijuana or K2/Spice also use other substances. In women who use drugs during pregnancy, there are often other confounding variables related to nutrition, prenatal care, and failure to disclose substance use because of concerns about adverse legal consequences."
However, she also cites a study she says found an association between prenatal cannabis exposure and increased frontal cortical thickness in children's brains. However, looking at that study from the Netherlands, mother of the 54 mother studied also used tobacco. Researchers concluded, "Prenatal cannabis exposure was not associated with global brain volumes, such as total brain volume, gray matter volume, or white matter volume."
A 2010 US Centers for Disease Control-sponsored population-based study determined, "Reported cannabis use does not seem to be associated with low birth weight or preterm birth." Volkow does not cite the CDC report in her article.
A seldom-cited study is Melanie Dreher's follow-up to her March of Dimes-funded Jamaican study finding that babies born to marijuana-smoking mothers performed BETTER on behavioral tests than their matched counterparts at age one month and no significant differences in developmental testing outcomes thereafter. NIDA refused to fund further follow ups to Dreher's studies.
Meanwhile, a study of 7,796 mothers published in JAMA Pediatrics concluded, “Children exposed prenatally to acetaminophen in the second and third trimesters are at increased risk of multiple behavioral difficulties, including hyperactivity and conduct problems,” and “Prenatal acetaminophen exposure at 32 weeks’ gestation was also associated with emotional problems.” Another recent study showed that mothers taking the anti-anxiety drug pregabalin were six times more likely to have a pregnancy with a major defect in the central nervous system than the women who were not taking the drug.
An Israeli Health Ministry committee is expected to rule that instead of a blanket prohibition on cannabis use during pregnancy, each case should be examined on it own merits.