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.

Marijuana is the most common illicit drug that is abused by pregnant women, and recently many states have adopted various levels of relaxed marijuana policies. The purpose of this study was to evaluate a potential association between residing in a state that allows medical marijuana use and maternal marijuana usage. Grounded in the theory of planned behavior, this study evaluated the prevalence and extent of maternal marijuana use in states that allow and states that do not allow medical marijuana use using the National Survey of Drug Use and Health (NSDUH). It was anticipated that more lenient subjective norms toward marijuana use and increased availability would support an increase of maternal marijuana use. The 2014 NSDUH was queried and analyzed using chi-square and logistic regression. The study revealed an increase of maternal marijuana use in states where medical marijuana was allowed, but the increase was not statistically significant. An increase of heavy users was observed in states where medical marijuana was allowed (54% versus 37%). Consistent with other research findings, this study revealed that young (OR = 3.56; 95% CI: 1.379, 9.213; p = 0.009) and unmarried (OR = 6.81; 95% CI: 2.485, 18.661; p < 0.001) pregnant woman were at higher risk for past month maternal marijuana use and had similar results for past year use. The unintended consequences of increased in utero marijuana exposure and its subsequent negative public health effects have been missing from the discussion of the relaxation of statewide marijuana policies. This study will provide policy makers responsible for changing marijuana policy with useful evidence on the unintended consequences of increased maternal marijuana use in areas where medical marijuana is allowed.