The effects of cigarette smoking and alcohol consumption on the length of gestation were examined in a prospective study of 30,596 pregnant women in northern California. Preterm births (<37 weeks' gestation) were 20% more common in women smoking at least one pack of cigarettes per day. This effect was strongest for births occurring before 33 weeks, where the excess was 60%. This excess was not accounted for by differences in maternal age, education, ethnicity, time prenatal care began, drinking during pregnancy, or eight other potential confounding factors. The results indicate a probable effect of smoking on the time of parturition, which is additional to its well-known effect on intrauterine growth retardation. The effect of alcohol consumption on preterm births was also examined, but no consistent trends were found.
Shiono PH, Klebanoff MA, Rhoads GG. Smoking and Drinking During PregnancyTheir Effects on Preterm Birth. JAMA. 1986;255(1):82–84. doi:10.1001/jama.1986.03370010088030
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