The influence of maternal smoking habits on the risk of subsequent stillbirth: is there a causal relation?

Abstract

Objective: Maternal smoking has previously been associated with risk of stillbirth. If women who quit smoking reduce their risk of stillbirth, the hypothesis of a causal association would be supported.

Design: Prospective cohort study.

Setting: Nationwide study in Sweden.

Population: All primiparous women who delivered their first and second consecutive single births between 1983 and 2001, giving a total number of 526,691 women.

Method: A population-based Swedish study with data from the Medical Birth Registry, the Immigration Registry and the Education Registry. Logistic regression analyses were used to estimate odds ratios, using 95% confidence intervals.

Main outcome measure: Stillbirth in the second pregnancy.

Results: Compared with nonsmokers in both pregnancies, women who smoked during the first pregnancy but not during the second do not have an increased risk of stillbirth (OR 1.02; 95% CI 0.79-1.30), while corresponding risk among women who smoked during both pregnancies was 1.35 (95% CI 1.15-1.58).

Conclusion: The result supports that maternal smoking during pregnancy is causally associated with stillbirth risk. Smoking is a preventable cause of stillbirth, and smoking interventions is an important issue in antenatal care.