With more and more people turning to legal marijuana for medical and recreational use, and dispensaries marketing it as a cure for morning sickness, a growing number of moms-to-be are using the drug in pregnancy. In 2017, 6.5 percent of pregnant women said they used marijuana, compared to 4.9 percent in 2012. But recent findings bolster the evidence that suggests their best bet is to just say no.
Published in the Journal of the American Medical Association (JAMA) by epidemiologist Daniel J. Corsi and colleagues, the study looked at a retrospective cohort of Ontario women between 2012 and 2017—resulting in 5,639 expectant mothers who reported that they used marijuana, who were matched to 92,873 pregnant women who said they didn’t.
Among these matched groups, the risk of preterm labour before 37 weeks gestation was almost 3 percent higher among the users—10.2 percent, as opposed to 7.2 percent in the nonusers. Researchers also found an increased risk of secondary outcomes that include babies being transferred to the NICU, a higher chance of being small for their gestational age, a lower Apgar score and placental abruption. On the flip side, however, a small protective association between using marijuana and the risk of preeclampsia and gestational diabetes was noted.
As with all studies, there were a few recognized shortcomings, like its reliance on registry data, which is hard to validate where substance use is concerned. The researchers were also unable to know the timing of cannabis exposure or how different doses affected different outcomes.
In the accompanying editorial, authors also likened the conversation around smoking up in pregnancy to other historical instances of substance studies in pregnant women, one being alcohol. While excessive drinking is accepted as an unnecessary risk for moms-to-be, the debate rages on where that occasional glass of wine is concerned. Some look at inconclusive data and see no proven risk, whereas others say abstinence is the only option in cases where a safe level hasn’t been proven.
Likewise, the data of this study could be interpreted in two very different ways. Some might be frightened by any amount of risk of preterm birth, while others may see the relief of morning sickness and other symptoms worth the small amount of increased risk, suggest the authors.
Still, the results are in line with other studies on maternal marijuana use, which have shown strong evidence pointing to low birth weight—a key indicator of overall health. A recent meta-analysis found that infants exposed to marijuana weighed about four ounces less than those who weren’t exposed. And an Ontario study of more than 26,000 births demonstrated that pregnant women who had used marijuana were three times more likely to have an infant with low birth weight.
It’s been established that cannabinoids can permeate the placenta into the fetal bloodstream, and the evidence is mounting that more research needs to be done before pregnant women can toke with confidence.