Pregnant women who smoke marijuana may increase their risk of stillbirth three-fold, a new study concludes.
Using other legal and illegal drugs, as well as smoking cigarettes and being exposed to secondhand smoke, also increases the risk.
HealthDay reports the researchers found 94 percent of mothers who had stillborn babies used one or more of these substances. The researchers found marijuana was the most common drug found in umbilical cord blood from stillborn infants. Marijuana was associated with a 2.8-fold increased risk of stillbirth.
"Because marijuana use may be increasing with increased legalization, the relevance of these findings may increase as well," said lead researcher Dr. Michael Varner of the University of Utah School of Medicine. Another study author, Dr. Uma Reddy of the U.S. National Institute of Child Health and Human Development, said it is not known why marijuana may increase the risk of stillbirth.
The study included 663 stillbirths and 1,900 live births. The researchers tested umbilical cord blood, and blood from the mothers, for a variety of illegal drugs. They also asked the mothers about their drug and tobacco use, and tested the mothers' blood for signs of tobacco use.
The study appears in the journal Obstetrics & Gynecology.