Smoking, maternal age, and fetal growth.

In a prospective clinical study from an unselected area-based population, the influence on birth weight for gestational age (standardized birth weight) was studied with special respect to risk factors for intrauterine growth retardation. Smoking was the most important risk factor: 16% of the mothers smoked at least ten cigarettes per day, and the influence of smoking on standardized birth weight was highly significant (P less than .001). Maternal age in itself had no effect on standardized birth weight. However, among smokers the reduction in standardized birth weight became more pronounced with increasing maternal age (P less than .001). Longterm smoking has been reported to increase the risk of severe placental complications. This study emphasizes that elderly smokers also must be considered to be at a higher risk than younger smokers for developing fetal growth disturbances.