BETHESDA, Md., Dec. 11 (UPI) -- Pregnant women who smoke tobacco or marijuana, take painkillers or use illegal drugs may double or even triple their risk of stillbirth, U.S. researchers say.
Dr. Uma M. Reddy of the Eunice Kennedy Shriver National Institute of Child Health and Human Development, Dr. Michael W. Varner of the University of Utah School of Medicine and colleagues calculated the increased risk of stillbirth for each of the substances they examined and found:
-- Tobacco use had 1.8-2.8 times greater risk of stillbirth, with the highest risk found among the heaviest smokers.
-- Marijuana use had 2.3 times greater risk of stillbirth.
-- Evidence of any stimulant, marijuana or prescription painkiller use had 2.2 times greater risk of stillbirth.
-- Passive exposure to tobacco had 2.1 times greater risk of stillbirth.
The researchers noted that they could not entirely separate the effects of smoking tobacco from those of smoking marijuana.
Only a small number of women tested positive for prescription painkiller use, but there was a trend toward an association of these drugs with an elevated stillbirth risk.
"As about 1-in-20 members of the U.S. population age 12 and older have used opioid pain relievers non-medically, this finding could affect many pregnant women and calls for more investigation," said study co-author Marian Willinger of the NICHD.
Stillbirth occurs when a fetus dies at or after 20 weeks of gestation.
The U.S. stillbirth rate decreased from 18 per 1,000 births in 1950 to 6 per 1,000 births in 2006, but it still remains higher than many other developed countries and affects almost 26,000 U.S. newborns per year.
The researchers enrolled women between March 2006 and September 2008 in five geographically defined areas delivering at 59 hospitals participating in the Stillbirth Collaborative Research Network External Web Site Policy.
Women who experienced a stillbirth and those who gave birth to a live infant participated in the study. The researchers tested blood samples at delivery from the two groups of women and the umbilical cords from their deliveries to measure the exposure to the fetus.
The research team also included researchers from Emory University, RTI International, the University of Texas' Medical Branch at Galveston and Health Science Center at San Antonio, and Brown University.