Smoking-associated fetal morbidity among older gravidas: a population study

We set out to assess the influence of advanced maternal age on fetal morbidity associated with smoking during pregnancy in a population-based retrospective study of 7 792 990 singleton live births between 1995 and 1997 in the United States with documented maternal smoking habit.

The study group consisted of infants born to mothers aged>or=40 years (older mothers). Two maternal age categories (20-29, "younger mothers"; 30-39, "mature mothers") were constructed as comparison groups. Adjusted odds ratios (ORs) generated from logistic regression models were used to compare fetal morbidity indices associated with smoking across maternal age categories. Main outcome measures included preterm, very preterm, and small for gestational age (SGA).

The prevalence of smoking was 13.1%, and decreased with increasing maternal age. Regardless of maternal age, the risk for fetal morbidity was significantly elevated if the mother smoked. The risks for preterm and SGA associated with smoking were significantly higher among older gravidas as compared to younger mothers while mature mothers had risk estimates comparable to those of older mothers. Among smoking mothers only, the risk pattern for fetal morbidity was J-shaped, with babies of older smokers having significantly higher fetal morbidity indices, while those of mature smokers showed lower levels of risk as compared to younger mothers.

In an era of relatively lower prevalence of smoking during pregnancy, advanced maternal age still increases the risk of smoking-associated fetal morbidity. Our findings reveal new information of elevated risk for very preterm births among older smoking mothers.