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. 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.