The impact of cocaine and marijuana use on low birth weight and preterm birth: a multicenter study.

Objective: Our aim was to evaluate prospectively the effects of cocaine and marijuana use on pregnancy outcomes.

Study Design: A prospective multicenter cohort study was conducted at seven university-based prenatal clinics in the United States from 1984 to 1989. The cohort described herein consisted of a multiethnic population of 7470 pregnant women. Information on the use of drugs was obtained from personal interviews at entry to the study and assays of serum obtained during pregnancy. Pregnancy outcome data (low birth weight [< 2500 gm], preterm birth [< 37 weeks' gestation], and abruptio placentae) were obtained with a standardized study protocol.

Results: A total of 2.3% of the women used cocaine and 11.0% used marijuana during pregnancy. Cocaine use was not associated with having a low-birth-weight infant (adjusted odds ratio 0.7, 95% confidence interval 0.4 to 1.3) or a preterm birth (1.3, 0.9 to 2.0). There was no association between short-term exposure to cocaine and preterm delivery (1.1, 0.3 to 4.0). However, cocaine use was strongly associated with abruptio placentae (adjusted odds ratio 4.2, 1.9 to 9.5). Marijuana use was not associated with low birth weight (1.1, 0.9 to 1.5), preterm delivery (1.1, 0.8 to 1.3) or abruptio placentae (1.3, 0.6 to 2.8). By comparison, 35% of the women smoked cigarettes during pregnancy, and cigarette smoking was positively associated with low birth weight (1.5, 1.2 to 1.8).

Conclusions: In this population of women receiving prenatal care, cocaine use was uncommon and was not related to most adverse birth outcomes. Marijuana use was relatively common and was not related to adverse pregnancy outcomes. Tobacco is still the most commonly abused drug during pregnancy, 15% of all cases of low birth weight in this study could have been prevented if women did not smoke cigarettes during pregnancy.