Coffee and alcohol intake, smoking and risk of multiple pregnancy

We analysed the relationship between coffee and alcohol intake, smoking and risk of multiple pregnancies using data from a case-control study on risk factors for multiple births conducted in Italy. Cases were 133 women who delivered multiple births not related to treatment for infertility (33 monozygotic and 100 dizygotic twins). Controls were 395 women admitted for normal delivery at the same clinic where cases had been identified. The odds ratios (OR) of multiple pregnancy were 1.5[95% confidence interval (CI) 0.8-2.8] and 2.0 (95% CI 1.0-3.7) for women drinking respectively one to two or three or more cups of coffee per day in comparison with non-coffee drinkers. Considering separately dizygotic and monozygotic pregnancies, the estimated OR were respectively for women drinking three or more cups of coffee, 1.7 and 3.1 for dizygotic and monozygotic pregnancies. The risk of multiple pregnancy tended to be higher in women drinking >or= 15 alcohol drinks per week: in comparison with tea-totallers the estimated OR for drink > or = 15 glasses per week were 2.3 and 2.6 respectively for dizygotic and monozygotic pregnancies. Heavy smokers (> or = 10 cigarettes per day) were at increased risk of multiple pregnancy: in comparison with never smokers, the estimated OR for multiple pregnancy was 1.6 (95% CI 0.9-2.7). Considering separately the two groups of multiple pregnancy, the OR of dizygotic and monozygotic pregnancy were 1.4 (95% CI 0.8-2.5) and 2.4 (95% CI 0.9-6.1) for women smoking > or = 10 cigarettes/day, but the trend in risk with number of cigarettes smoked per day and duration of the habit was not significant.