Sudden infant death risk rises linearly with amount smoked by mothers

1. Infants of mothers who smoked at least 1 cigarette daily during pregnancy had more than doubled risk of sudden unexpected infant death (SUID). After 1 cigarette, there was a linear increase in risk per daily cigarette.

2. Smoking before pregnancy also increased risk of SUID, whereas reducing use or quitting before or during pregnancy were associated with reductions in risk.

Evidence Rating Level: 2 (Good)

Study Rundown: Rates of SUID in the United States have fallen due to increased public awareness of the importance of infant sleep position and environment. At the same time, the relative contribution of prenatal smoking to SUID has risen, but less was known about the contribution of smoking before pregnancy, smoking reduction, and smoking cessation. In this retrospective cross-sectional study, researchers used Centers for Disease Control and Prevention birth data and maternal smoking data to examine the relationship between smoking before and during pregnancy and SUID. Risk of SUID was twice as high among mothers who smoked at least 1 cigarette daily during pregnancy, compared to mothers who did not smoke. For each additional cigarette daily, there was a linear increase in risk until 20 cigarettes, after which risk plateaued. Compared to continuous smoking, reducing use or quitting during pregnancy was associated with reduced risk. Smoking before pregnancy increased risk of SUID, though the increase in risk was lower for mothers who quit before pregnancy.

These findings are limited by self-reported maternal smoking rates, which do not include environmental smoke exposure including paternal smoking. Furthermore, 40% of births in the dataset did not have associated smoking data. Nonetheless, the study is strengthened by its large, nationally comprehensive sample and higher resolution compared to prior studies. For physicians, these findings highlight the importance of screening for smoking habits both before and during pregnancy, and working with mothers to reduce or cease use before pregnancy or as early in pregnancy as possible.

Click to read the study, published today in Pediatrics

Relevant reading: Smoking and the Sudden Infant Death Syndrome

Study author, Tatiana M. Anderson, PhD, speaks to 2 Minute Medicine: Center for Integrative Brain Research, Seattle Children’s Research Institute, Seattle, Washington.

“This study uses advanced computational modeling techniques on US vital statistics data to show that any amount of smoking – even a single cigarette per day – during pregnancy doubles the risk of sudden unexpected infant death (SUID). It is important for doctors to strongly encourage non-smoking practices, even well before pregnancy; but patients whom cannot quit entirely should be advised that each cigarette that is reduced on average per day can measurably decrease the risk of SUID.”

In-Depth [retrospective cohort]: Researchers used birth data and self-reported maternal smoking data from the Centers for Disease Control and Prevention Birth Cohort Linked Birth/Infant Death Data Set for all births between 2007 and 2011 to identify 10 737 SUID cases among 12 417 813 births with complete prenatal smoking information. The study measured the relationship between SUID and number of cigarettes smoked per day before and during pregnancy using a generalized additive model. Adjustments were made for race and ethnicity, mother and father’s age, mother’s marital status and education, number of prenatal visits, gestational length, and birth weight.

Infants of mothers who smoked during pregnancy had more than doubled risk of SUID (adjusted odds ratio [aOR] = 2.44; 95% confidence interval [CI] = 2.31–2.57) compared to infants of mothers who did not smoke. Smoking 1 cigarette daily throughout pregnancy was associated with a twofold increased risk of SUID (aOR = 1.98; 95% CI = 1.73–2.28), and there was a positive linear relationship between number of cigarettes smoked daily, with each additional cigarette smoked per day increasing odds of SUID by 0.07 (aOR = 0.07 x number of daily cigarettes + 1.91) which plateaued after 20 daily cigarettes. Among mothers who smoked in the 3 months before pregnancy, SUID risk was lowest for those who quit before pregnancy (aOR = 1.47; 95% CI 1.16 – 1.87), compared with mothers who did not smoke before or during pregnancy. Reducing smoking during pregnancy was associated with slightly decreased risk of SUID compared with continued smokers.

Image: PD

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