Week-by-week alcohol consumption in early pregnancy and spontaneous abortion risk: a prospective cohort study

Background: Half of women use alcohol in the first weeks of gestation, but most stop once pregnancy is detected. The relationship between timing of alcohol use cessation in early pregnancy and spontaneous abortion risk has not been determined.

Objective: This study aimed to evaluate the association between week-by-week alcohol consumption in early pregnancy and spontaneous abortion.

Study design: Participants in Right from the Start, a community-based prospective pregnancy cohort, were recruited from 8 metropolitan areas in the United States (2000-2012). In the first trimester, participants provided information about alcohol consumed in the prior 4 months, including whether they altered alcohol use; date of change in use; and frequency, amount, and type of alcohol consumed before and after change. We assessed the association between spontaneous abortion and week of alcohol use, cumulative weeks exposed, number of drinks per week, beverage type, and binge drinking.

Results: Among 5353 participants, 49.7% reported using alcohol during early pregnancy and 12.0% miscarried. Median gestational age at change in alcohol use was 29 days (interquartile range, 15-35 days). Alcohol use during weeks 5 through 10 from last menstrual period was associated with increased spontaneous abortion risk, with risk peaking for use in week 9. Each successive week of alcohol use was associated with an 8% increase in spontaneous abortion relative to those who did not drink (adjusted hazard ratio, 1.08; 95% confidence interval, 1.04-1.12). This risk is cumulative. In addition, risk was not related to number of drinks per week, beverage type, or binge drinking.

Conclusion: Each additional week of alcohol exposure during the first trimester increases risk of spontaneous abortion, even at low levels of consumption and when excluding binge drinking.