Cannabis use during pregnancy may cause mental health problems in children

Children whose mothers used cannabis after the fifth or sixth week of pregnancy may be more likely to develop mental health problems in early adolescence, a new study suggests.

An analysis of data from more than 10,000 children aged 11 and 12 revealed that exposure to cannabis in utero was associated with a higher risk of developing disorders such as ADHD, aggressive behavior, conduct disorder and rule-breaking behavior, according to the report published in JAMA Pediatrics.

The take-home message from this study is that there is some evidence that one should be cautious about using cannabis during pregnancy. The new study is an association and can’t prove that cannabis is the cause of the mental health problems.

However, the results fall in line with earlier research on the same children, who were participants in the ongoing Adolescent Brain Cognitive Development (ABCD) study. The long-term project, which is supported by the National Institutes of Health, has been tracking the brain development of nearly 12,000 children via MRI scans.

A 2019 study that looked at the children when they were 9 and 10 found the same association between prenatal cannabis and behavioral issues. It also showed that children exposed to cannabis in utero tended to have lower birth weight, lower brain volume and lower white matter volume.

While the percentage is still small, the number of women using cannabis during pregnancy is increasing. According to a government survey, 4.7 percent of pregnant women reported using marijuana in 2018 and 5.4 percent in 2019.

For pregnant women who rely on marijuana to help with nausea, Baranger advised talking to their health care provider.

Baranger and his colleagues analyzed data from 10,631 children who were participating in the NIH brain study. The researchers compared three groups of children:

• Those whose mothers did not use cannabis during pregnancy.

• Those whose mothers were using cannabis but quit when they learned they were pregnant.

• Those whose mothers continued to use cannabis after learning they were pregnant.

The impact of cannabis use was seen in the middle of the first trimester. Use of it earlier in the pregnancy — before the moms discovered they were pregnant — did not appear to have an impact on the risk of the children developing behavior issues, Baranger said. He suspects that is because cannabinoid receptors haven’t developed in the fetal brains yet.

The new research is saying that the issues found in the earlier study persist in kids who are 12, said Staci Gruber, an associate professor of psychiatry at the Harvard Medical School, director of the Marijuana Investigations for Neuroscientific Discovery (MIND) Program and the Cognitive and Neuroimaging Core at Harvard’s McLean Hospital.

It’s not hard to imagine why cannabis might appeal to some women, Gruber said. “You can understand why they might turn to something like this,” she added. “They might think it’s natural and won’t hurt anything.”