Background: Pregnancy substance use is linked to low birth weight. However, less is known about relative contributions of various substances and whether effects are due to decreased gestational duration, restriction of fetal growth, or both. The study goal was to use causal modeling to evaluate the individual impact of alcohol, tobacco, cocaine, and marijuana on gestational duration and fetal growth.
Methods: Participants were 3164 urban black women recruited at entry to prenatal care and followed to delivery, with all gestational dating ultrasound supported. Pregnancy substance use was assessed via self-report (alcohol, tobacco, cocaine, and marijuana).
Results: Alcohol, cigarette, and cocaine use were all individually and negatively related to gestational age at delivery. However, only alcohol, cigarette, and marijuana use predicted fetal growth, with effects for alcohol and cigarette greater and more discrepant for older women. Overall, heavy cigarette smoking had the greatest individual impact on birth weight (up to 431 g). Heavy levels of use of all 4 substances by older women decreased birth weight by 26% (806 g).
Conclusions: For perhaps the first time, reduced birth weight is apportioned both by type of substance and mechanism of effect. The use of alcohol and/or cigarettes was clearly more harmful to fetal growth than cocaine use. Findings demonstrate the need for continued emphasis on intervention efforts to address legal and illicit pregnancy substance use.