Maternal age modifies the effect of maternal smoking on intrauterine growth retardation but not on late fetal death and placental abruption.

To investigate whether the effect modification of smoking by maternal age previously reported for small for gestational age births was also obtained for late fetal death and placental abruption, the author analyzed single births in Sweden (n = 1,057,711) from 1983 to 1992. An effect modification of smoking by maternal age was obtained only with regard to fetal growth: Compared with nonsmokers aged 40-44 years, the risk of small for gestational age births among women smoking at east 10 cigarettes per day in the same age group was 4.5, whereas the corresponding risk increase among teenagers was only 2.0. The present results support the hypothesis that smoking actually influences fetal growth more among older smokers.