The reasons for spontaneous abortion are diverse and most likely include both genetic and environmental factors. Illicit drugs, primarily cocaine, are among the environmental factors implicated in spontaneous abortion. Ness and colleagues performed a case-control study of the influence of cocaine use and cigarette smoking on pregnancy outcome.

The study included 970 inner-city adolescents and women who presented to an urban emergency department for a variety of reasons. Urine pregnancy tests were used to confirm pregnancy, and the patient's report of her last menstrual period was used to estimate gestational age. Women were excluded from the study if their last normal menstrual period had been more than 22 weeks previously or within the past 28 days.

A 45-minute baseline interview was conducted to obtain information about cocaine, marijuana, alcohol and tobacco use. Blood, urine and hair samples were assessed for the presence of the major metabolites of cocaine, marijuana, amphetamines, opiates and nicotine. Follow-up telephone interviews were conducted at 16 and 22 weeks' gestation to determine the status of the pregnancy. A spontaneous abortion was defined as a pregnancy loss before 22 weeks' gestation. This loss was confirmed by pelvic examination, ultrasound examination and serial measurement of the serum human chorionic gonadotropin level.

The mean duration of pregnancy was 10 weeks at the time of entry into the study. Spontaneous abortion occurred in 400 women, and the remaining 570 were pregnant after 22 weeks' gestation. Hair analysis in the women who had a spontaneous abortion demonstrated that 28.9 percent had used cocaine, compared with 20.5 percent of those who did not have a spontaneous abortion. Urine cotinine was detected in 34.6 percent of the group with spontaneous abortion, compared with 21.8 percent of those who did not have a spontaneous abortion. Evidence of both cocaine and nicotine use was independently associated with a risk of spontaneous abortion. Calculated risk estimates demonstrated that cocaine and cigarette smoking accounted for 8 percent and 16 percent, respectively, of the spontaneous abortions. Marijuana and alcohol use did not independently relate to a risk of spontaneous abortion. No dose-response relationship was found between the amount of cocaine in the hair sample and the risk of spontaneous abortion.

The authors conclude that cocaine use and cigarette smoking in early pregnancy contribute to the occurrence of spontaneous abortion. The results suggest that cigarette smoking and cocaine use are independently associated with an increased risk of spontaneous abortion.