Infant Morbidity and Mortality Attributable to Prenatal Smoking in the United States

Abstract

Despite the continuing reduction in the incidence of smoking during pregnancy in the United States, prenatal smoking is still one of the most prevalent and preventable causes of infant morbidity and mortality. Two previous studies estimated that 5% to 6% of all infant deaths during 1995 to 1997 were due to prenatal smoking. In 2004, the Surgeon General's report concluded that there was sufficient evidence to show a clear association between prenatal smoking and several causes of infant morbidity and mortality. This study provides updated estimates of the percentage of preterm deliveries, term low-birth-weight deliveries <2500 g, and infant deaths because of smoking—individual outcomes identified in the Surgeon General's report as causally related to prenatal smoking in the United States. The updated estimates were based on the most recent and complete US vital statistical data. The US Linked Birth/Infant Death Data Set, 2002 birth cohort included a final sample of 3,352,756 singleton live births. Live birth outcomes were grouped into 5 delivery groups: very preterm (27 completed weeks of gestation), moderately preterm (28-33 completed weeks), late preterm (34-36 completed weeks), term low birth weight (≥37 completed weeks and <2500 g), sudden infant death syndrome (SIDS), and infant deaths from preterm-related causes. Multiple logistic regression models estimated the proportion of adverse birth outcomes attributable to prenatal smoking. Of the 3,352,756 singleton live infants delivered in 2002, 11.5% (n = 386,262) were exposed to prenatal smoking. The percentage of all infant deaths attributable to prenatal smoking was estimated to be 2.8% to 4.1 %. Prenatal smoking was associated with very (adjusted odds ratio [aOR], 1.5; 95% confidence interval [CI], 1.4-1.6); moderate (aOR, 1.4; 95% CI, 1.4-1.4); and late (aOR, 1.2; 95% CI, 1.2-1.3) preterm deliveries and term low-birth-weight deliveries (aOR, 2.3; 95% CI, 2.3-2.5) compared with term ≥2500 g deliveries. Prenatal smoking was also associated with SIDS (aOR, 2.7; 95% CI, 2.4-3.0) and preterm-related deaths (aOR, 1.5; 95% CI, 1.4-1.6). The percentage of adverse birth outcomes attributable to prenatal smoking and thereby, potentially avoidable was 5.3% to 7.7% of preterm deliveries, 13.1 % to 19.0% of term low-birth-weight deliveries, 23.2% to 33.6% of SIDS, and 5.0% to 7.3% of preterm-related deaths. Provided that rates of prenatal smoking continued to decline, estimates for the fraction of preterm-related deaths and SIDS deaths attributed to prenatal smoking in 2009 were slightly lower (4.4%-6.3% for preterm-related deaths and 20.2%-29.3% for SIDS deaths). These findings demonstrate that despite the continuing decline in rates of prenatal smoking, a substantial proportion of avoidable cases of infant morbidity and mortality is associated with prenatal smoking.