Maternal alcohol use and medically indicated vs. spontaneous preterm birth outcomes: a population-based study.

BACKGROUND: The aetiology of preterm birth remains poorly understood. The purpose of this study is to investigate if an association exists between prenatal alcohol consumption and preterm birth and to determine if such an association differs by subcategories of preterm birth. METHODS: We employed vital statistics data from the state of Missouri covering the period 1989-2005 (n = 1 221 677 singleton records). The outcome of interest was preterm birth, subclassified into medically indicated and spontaneous phenotypes. Multivariate logistic regression was used to generate adjusted odds ratios, with non-drinking mothers as the referent category. RESULTS: Prenatal alcohol use was associated with elevated risk for preterm birth. The strength of association was more prominent for spontaneous preterm delivery {adjusted odds ratio (AOR) [95% confidence interval (CI)] = 1.34 (1.28-1.41)} than for medically indicated preterm birth [AOR (95% CI) = 1.16 (1.05-1.28)]. The overall risk for drinking-related spontaneous preterm birth increased with incremental rise in the number of drinks consumed per week (P for trend < 0.01). CONCLUSIONS: Prenatal alcohol use is a risk factor for preterm delivery, and especially for spontaneous preterm birth. These findings enhance our understanding of the aetiology of preterm birth and could be utilized in the development of appropriate prevention strategies that will assist in decreasing perinatal mortality and morbidity associated with preterm delivery.