Cannabis exposure linked to 1.5 times higher risk of unhealthy pregnancy outcomes

In a large study of more than 9,000 pregnant people from across the U.S., researchers at University of Utah Health have found that cannabis exposure during pregnancy is associated with a composite measure of unhealthy pregnancy outcomes, especially low birth weight, and that higher exposure is associated with higher risks.

Compared to most prior studies, this study was larger and measured cannabis exposure more accurately, which allowed researchers to distinguish the effects of cannabis itself from those caused by other correlated health conditions. The research publishes online on December 12 in JAMA.

In the past ten years, the percentage of Americans who use medical marijuana has more than doubled as state-level legalization becomes increasingly common. But despite its prevalence as a medication, the full health effects of cannabis remain unknown, especially for specific populations—such as pregnant people—that might be especially at risk of health complications.

The scientists found that cannabis exposure was associated with a 1.5-fold increase in risk: 26% of cannabis-exposed pregnant people experienced an unhealthy pregnancy outcome, versus 17% of non-exposed pregnant people. Higher levels of cannabis exposure over the course of pregnancy were associated with higher risks.

A distinguishing feature of the study was how the researchers measured cannabis exposure. While other studies had asked participants to report their own cannabis use (which has been shown to underestimate the actual rate of use by two or three times), the scientists measured the levels of a metabolic byproduct of cannabis in participants’ urine samples, which gave more accurate measurements of cannabis exposure.

Reference: Cannabis exposure linked to 1.5 times higher risk of unhealthy pregnancy outcomes; JAMA, DOI: 10.1001/jama.2023.21146