Alcohol consumption among first-time mothers and the risk of preterm birth: a cohort study.

PURPOSE: Our aim was to explore the association between alcohol consumption, before and during pregnancy, and the risk of preterm birth among 46,252 primiparous mothers.

METHODS

We obtained information on alcohol consumption from questionnaire responses at pregnancy week 15 from the prospective, observational Norwegian Mother and Child Cohort Study. Data on preterm birth, categorized as delivery before gestation week 37, were retrieved from the Medical Birth Registry of Norway.

RESULTS

Among the participants, 91% consumed alcohol before pregnancy and fewer than 20% reported consuming alcohol during pregnancy. The adjusted odds ratio (aOR) for preterm birth associated with prepregnancy alcohol consumption was 0.81 (95% confidence interval [CI], 0.70-0.95). We did not find a risk reduction for overall drinking during pregnancy, aOR = 1.03 (95% CI, 0.90-1.19). However, dose-response analyses showed tendencies toward adverse effects when drinking 1-3 times per month during the first 15 weeks of pregnancy, aOR = 1.51 (95% CI, 1.14-2.00).

CONCLUSIONS

We did not find any effects of alcohol consumption during pregnancy, whereas pre-pregnancy drinking was associated with reduced risk of preterm birth. Residual confounding may have influenced the risk estimates, especially before pregnancy, as nondrinkers have lower socioeconomic status and well-being than drinkers.