The effect of health compromising behaviors on preterm births.

Objectives: The objective of our study was to determine whether there were combined effects of smoking, alcohol, and illicit drug use during pregnancy on the frequency of preterm births, and if so, the magnitude of the association after adjusting for confounding factors.

Methods: We conducted a retrospective cohort study of singleton live births in Kansas City, Missouri from 1990-2002. We defined health compromising behaviors as the use of cigarettes, alcohol, and illicit drugs. The effect of these behaviors on preterm births was considered for each substance individually, and in combination. The rates of preterm births for these groups were calculated. Using logistic regression, adjusted odds ratios were used to estimate the relative risk of preterm births among these groups.

Results: Over 13% of infants born to women who smoked were preterm, compared to 9.6% for non-smokers. Of infants born to women who reported alcohol use, 17.3% were preterm compared to 10.1% for non-drinkers. Smoking and alcohol use in combination was associated with 18.0% preterm births, while alcohol and drug use in combination was associated with 20.8% preterm births. The use of all three substances was associated with 31.4% preterm births.

Conclusion: Women who engaged in health compromising behaviors during pregnancy showed an increased proportion of preterm births compared to those who did not. There is significant interaction between these behaviors leading to higher rates of preterm births than predicted by their additive effects. To decrease preterm births, we must deal with the effects of smoking, drinking, and drug use simultaneously.