SOCIODEMOGRAPHIC AND CLINICAL-VARIABLES MODIFYING THE SMOKING-RELATEDRISK OF LOW-BIRTH-WEIGHT

Objective: The purpose of the study was to evaluate the sociodemograph ic and clinical variables modifying the smoking-related risk of low bi rth weight (<2500 g). Method: This case-control study included a popul ation of 967 singleton low birth weight deliveries and 967 selected co ntrols. Unconditional logistic regression analysis was used to test st atistical significance of the interactions between smoking in pregnanc y and other risk factors for low birth weight. Results: Increasing mat ernal age and parity potentiate the smoking-related risk of a low birt h weight infant. The effect of maternal smoking on the risk of low bir th weight was significantly increased in patients with a history of pr evious spontaneous abortion (excess risk 2.30, 95% C,I, 1.24-4.27) and in patients of high compared with patients of intermediate or low soc ial class (excess risk 1.97, 95% C.I, 1.1-3.57). Smokers with less tha n two prenatal visits per trimester were at significantly greater risk of delivering a low birth weight infant (excess risk 2.36, 95% C.I. 1 .14-4.87) than their counterparts with more frequent prenatal visits. Among clinical variables, the effect of maternal smoking on the risk o f low birth weight was significantly increased in women with a history of first trimester hemorrhage during the current pregnancy (excess ri sk 2.67, 95% C,I, 1.30-5.49). Conclusions: The smoking-related risk of low birth weight is very high in some subgroups of women. Identificat ion of these subgroups could be important for prenatal counseling.