Smoking and the occurrence of congenital malformations and spontaneous abortions: multivariate analysis.

A multivariate analysis was carried out with retrospective data on the effects of tobacco smoking on congenital malformations and spontaneous abortions. Congenital malformations were collected from the Finnish Register of Congenital Malformation. Tens of possible confounding variables, including maternal and family characteristics, obstetric history, medicine taking, and diseases during the pregnancy, were taken into consideration. In the final analysis 13 confounders were controlled. The odds ratios for the smoker's child to be born with central nervous system, oral cleft, or musculoskeletal malformations were 1.25, 1.25, and 0.75, respectively. All the differences were statistically nonsignificant. The effect of smoking on spontaneous abortions was analyzed by means of a questionnaire study on hospital personnel. The smokers of over 10 cigarettes per day had more spontaneous abortions than the nonsmokers, but the differences were not significantly statistically. The data were controlled for age, parity, and coffee and alcohol drinking.