The effect of antismoking intervention during pregnancy: an assessment of interactions with maternal characteristics.

In a previous experimental study, which included 935 pregnant smokers recruited from private obstetric practices located in a large metropolitan area and from one hospital obstetric clinic, a 92-g difference was found between infants born to women who had antismoking intervention and those born to women in a control group. The current report further examines the effect of intervention on both smoking cessation during pregnancy and birth weight. Specific attention is given to interactions between intervention and maternal characteristics. These maternal characteristics were determined at the time of first prenatal care. A stepwise regression analysis was performed to assess 1) the association of each maternal variable with smoking cessation and birth weight; 2) the effect of intervention on these outcomes after adjusting for the maternal variable; and 3) the interaction effect between intervention and the maternal variable. The effect of intervention on smoking cessation was found to be significantly greater for women who experienced problems early in pregnancy, such as high blood pressure and urinary tract infection. The beneficial effect of intervention on birth weight decreased with age and number of previous low birth weight infants but increased with previous fetal loss. There is some evidence to suggest that the effect of intervention on birth weight is also dependent on the amount of smoking prior to intervention.