There are plenty of guidelines about how to navigate a healthy pregnancy, on topics as diverse as drinking alcohol to having sex while pregnant. But at least one aspect of modern life is still lacking research when it comes to its effects on pregnant people and child development: smoking weed. Some research suggests that smoking weed during pregnancy may be linked to low birth weight, preterm birth, and autism. But otherwise, experts just aren’t sure how marijuana could affect a developing fetus. Now, however, they have some clues. A new study finds that children exposed to cannabis during pregnancy may suffer developmental and behavioral issues early in life.
The new study, designed to assess what exposure to marijuana in utero could mean for child development and mental health, focused on a few measurements in kids, including behavior, hormone levels, and heart rate variability. Particularly, the researchers note that they were looking for anxiety-related issues. The results were published today in Proceedings of the National Academy of Sciences.
The study examined more than 300 parent-child pairs, split into those who used marijuana during pregnancy and those who didn’t. The researchers took hair samples from the kids to test for hormone levels, observed their behavior using a standard assessment, measured their heart rates, and took samples of the placenta.
They found that kids exposed to weed in the womb had higher average levels of cortisol, often called the “stress hormone.” Cortisol plays an important role in our bodies, but a higher level maintained over time is associated with long-term stress. The researchers also found significant differences between the two groups in a type of heart rate variability that can also be associated with stress. In addition, kids exposed to cannabis during pregnancy had significantly higher than average levels of aggression, anxiety and hyperactivity compared to the non-marijuana group. However, this study is not nearly enough to say that smoking weed during pregnancy causes any of these conditions or behaviors.
The researchers speculated that these differences could stem from differences in gene expression in the placenta. They found that some immune-related genes were expressed differently between the two groups, in ways that could potentially account for the higher anxiety levels observed in kids exposed to marijuana during fetal development. This indicates that using marijuana during pregnancy could lead to other long-term impacts on these kids too, Yasmin Hurd, PhD, a neuroscientist at Mount Sinai Hospital in New York and one of the study’s authors, told Fatherly.
Right now, the Centers for Disease Control and Prevention recommends against smoking weed during pregnancy, and studies such as this show that pre-natal exposure could be detrimental to kids. But, especially since weed is just now becoming more widely used, more studies are needed to fully understand the relationship between weed and child development.
Part of the reason for the overall shortage of studies on marijuana during pregnancy is that marijuana is still illegal at the federal level, and hardly any states had legalized weed until recently. But as legalization comes in rapid succession to many states, people are encountering weed in their lives a whole lot more — and weed use among pregnant people has also increased recently.
“Legalization of cannabis has made many people think that it is without any health risk,” Hurd says. But smoking weed during pregnancy is not innocuous and likely comes with risks that are still unknown.