Smoking tobacco or marijuana, taking prescription painkillers, or using illegal drugs during pregnancy is associated with double or even triple the risk of stillbirth, according to research funded by the National Institutes of Health.
Researchers based their findings on measurements of the chemical byproducts of nicotine in maternal blood samples; and cannabis, prescription painkillers and other drugs in umbilical cords.
Taking direct measurements provided more precise information than did previous studies of stillbirth and substance use that relied only on women's self-reporting. The study findings appear in the journal Obstetrics & Gynecology.
"Smoking is a known risk factor for stillbirth, but this analysis gives us a much clearer picture of the risks than before," said senior author Uma M. Reddy, M.D., MPH, of the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD), the NIH institute that supported the study. "Additionally, results from the latest findings also showed that likely exposure to secondhand smoke can elevate the risk of stillbirth."
Dr. Reddy added, "With the legalization of marijuana in some states, it is especially important for pregnant women and health care providers to be aware that cannabis use can increase stillbirth risk."
The study enrolled women between March 2006 and September 2008 in five geographically defined areas delivering at 59 hospitals participating in the Stillbirth Collaborative Research Network (https://scrn.rti.org/). 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. They also asked participants to self-report smoking and drug use during pregnancy.
Stillbirth occurs when a fetus dies at or after 20 weeks of gestation. While the U.S. stillbirth rate decreased from 18 per 1,000 births in 1950 to 6 per 1,000 births in 2006, it still remains higher than many other developed countries and affects almost 26,000 U.S. newborns per year.
Dr. Reddy collaborated with first author Michael W. Varner, M.D., of the University of Utah School of Medicine, in Salt Lake City, and network researchers from Emory University, in Atlanta, GA; RTI International, in Research Triangle Park, NC; the University of Texas Medical Branch at Galveston; the University of Texas Health Science Center at San Antonio; Brown University, in Providence, RI, and the NICHD, in Bethesda, MD.
The researchers tested the women's blood for cotinine, a derivative of nicotine, and tested fetal umbilical cords for evidence of several types of drugs. They looked for evidence of the stimulants cocaine and amphetamine; prescription painkillers, such as morphine and codeine, and marijuana. These tests reflect exposure late in pregnancy.
Among the women who had experienced a stillbirth, more than 80 percent showed no traces of cotinine and 93 percent tested negative for the other drugs. In comparison, about 90 percent of women who gave birth to a live infant tested tobacco-free and 96 percent tested negative for other drugs.
Based on the blood test results and women's own responses, the researchers calculated the increased risk of stillbirth for each of the substances they examined:
• Tobacco use - 1.8 to 2.8 times greater risk of stillbirth, with the highest risk found among the heaviest smokers
• Marijuana use - 2.3 times greater risk of stillbirth
• Evidence of any stimulant, marijuana or prescription painkiller use-2.2 times greater risk of stillbirth
• Passive exposure to tobacco - 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 towards an association of these drugs with an elevated stillbirth risk.
"As about 1 in 20 members of the U.S. population over the age of 12 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, Ph.D., also of the NICHD.