Expectant mothers who smoke marijuana may increase their risk of stillbirth, according to a new study. Researchers from the University of Utah School of Medicine have found that marijuana use during pregnancy is associated with a threefold increase in the risk of fetal death — even when the mother uses no other substances. At a time when more and more states are relaxing their cannabis policies, the findings may inspire new health recommendations and prenatal care protocols.

Published in the journal Obstetrics and Gynecology, the new study surveyed the relationship between stillbirth and a range of different drug-related risk factors. The authors found that even in the absence of other factors, marijuana use corresponded to an elevated risk. “When [the results are] controlled for cigarette smoking, marijuana use is [still] associated with an increased risk of stillbirth," lead researcher Dr. Michael Varner said.  "Because marijuana use may be increasing with increased legalization, the relevance of these findings may increase as well.”

The review examined 663 stillbirths recorded between March 2006 and September 2008. In their analysis, the researchers tested umbilical cord blood samples as well as maternal blood samples. The values were then compared to data derived from about 1,900 live births.

Dr. Varner and his team found 94 percent of stillbirths were associated with some type of substance use. The most common substance was marijuana, which corresponded to a 2.8-fold increase in risk, Health Day reported. Other significant factors included cigarette smoking and exposure to secondhand smoke.  “It's clear there is an increased risk of stillbirth with marijuana,” senior author Uma Reddy explained. “Some of it is overlapping with smoking cigarettes, and we know that cigarette use is also associated with stillbirth.”

Although the study falls short of establishing a hard, causal relationship between marijuana and stillbirth, Reddy and her team believe that its message is pretty clear: Don’t smoke anything during pregnancy.  “If you smoke, stop,” the researchers wrote. “You should not use marijuana during pregnancy."

This pithy sentiment is shared by a large number of medical experts. Many argue that when it comes to adverse pregnancy outcomes, it doesn’t really make sense to discriminate between causation and correlation. If a substance could conceivable result in stillbirth, premature birth, or other complications, one should simply play it safe and stay away from it. "We don't want our patients, either before they become pregnant or during pregnancy, to either smoke or use anything that is not medically necessary, like marijuana or even prescription drugs, OB/GYN Jill Rabin of the Long Island Jewish Medical Center told reporters. 

Source: Varner MW, Silver RM, Rowland H et al. Association Between Stillbirth and Illicit Drug Use and Smoking During Pregnancy.Obstetrics & Gynecology.2013.