Systematic Review and Meta-Analyses of Perinatal Death and Maternal Exposure to Tobacco Smoke During Pregnancy

Abstract

We conducted a systematic review and 3-part meta-analysis to characterize the relationship between smoking and perinatal death, defined as the combination of stillbirth and neonatal death. The PubMed database was searched (1956-August 31, 2011) with keywords, and manual reference searches of included articles and Surgeon Generals' reports were conducted. The full texts of 1,713 articles were reviewed, and 142 articles that examined the associations between active or passive smoking and perinatal death were included in the meta-analyses. Data were abstracted by 2 reviewers. Any active maternal smoking was associated with increased risks of stillbirth (summary relative risk (sRR) = 1.46, 95% confidence interval (CI): 1.38, 1.54 (n = 57 studies)), neonatal death (sRR = 1.22, 95% CI: 1.14, 1.30 (n = 28)), and perinatal death (sRR = 1.33, 95% CI: 1.25, 1.41 (n = 46)). The risks of stillbirth, neonatal death, and perinatal death increased with the amount smoked by the mother. Biases in study publication, design, and analysis were present but did not significantly affect the results. These findings strengthen the evidence that women should not smoke while pregnant, and all women of reproductive age should be warned that smoking increases the risks of stillbirth, neonatal death, and perinatal death.

Keywords: neonatal death; perinatal death; perinatal mortality; pregnancy; smoking; stillbirth; tobacco.

Figure 1.

Selection of published studies (1948–August 31, 2011) included in a systematic review and 3-part meta-analysis of smoking and risk of perinatal death.

Figure 2.

Relative risk of stillbirth according to number of cigarettes smoked per day during pregnancy, calculated using 22 published studies and 65 data points and excluding open-ended categories of cigarettes per day (1 study and 24 data points). Solid line, relative risk; dotted-dashed lines, 95% confidence interval.

Figure 3.

Relative risk of neonatal death according to number of cigarettes smoked per day during pregnancy, calculated using 10 studies and 32 data points and excluding open-ended categories of cigarettes per day (0 studies and 10 data points). Solid line, relative risk; dotted-dashed lines, 95% confidence interval.