Concurrent prenatal drinking and smoking increases risk for SIDS: Safe Passage Study report

Abstract

Background

Sudden infant death syndrome (SIDS) is the leading cause of postneonatal mortality. Although the rate has plateaued, any unexpected death of an infant is a family tragedy thus finding causes and contributors to risk remains a major public health concern. The primary objective of this investigation was to determine patterns of drinking and smoking during pregnancy that increase risk of SIDS.

Methods

The Safe Passage Study was a prospective, multi-center, observational study with 10,088 women, 11,892 pregnancies, and 12,029 fetuses, followed to 1-year post delivery. Subjects were from two sites in Cape Town, South Africa and five United States sites, including two American Indian Reservations. Group-based trajectory modeling was utilized to categorize patterns of drinking and smoking exposure during pregnancy.

Findings

One-year outcome was ascertained in 94·2% infants, with 28 SIDS (2·43/1000) and 38 known causes of death (3·30/1000). The increase in relative risk for SIDS, adjusted for key demographic and clinical characteristics, was 11·79 (98·3% CI: 2·59–53·7, p < 0·001) in infants whose mothers reported both prenatal drinking and smoking beyond the first trimester, 3.95 (98·3% CI: 0·44–35·83, p = 0·14), for drinking only beyond the first trimester and 4·86 (95% CI: 0·97–24·27, p = 0·02) for smoking only beyond the first trimester as compared to those unexposed or reported quitting early in pregnancy.

Interpretation

Infants prenatally exposed to both alcohol and cigarettes continuing beyond the first trimester have a substantially higher risk for SIDS compared to those unexposed, exposed to alcohol or cigarettes alone, or when mother reported quitting early in pregnancy. Given that prenatal drinking and smoking are modifiable risk factors, these results address a major global public health problem.

Funding

National Institute on Alcohol Abuse and Alcoholism, Eunice Kennedy Shriver National Institute of Child Health and Human Development, and the National Institute on Deafness and Other Communication Disorders.

Research in Context

 Evidence before this study

Exposure of the fetus to alcohol and/or tobacco (smoking) increases risk for a wide range of neurodevelopmental problems after birth. Among these, the most devastating is unexpected, unexplained death during infancy. Many studies have shown that the risk of Sudden Infant Death Syndrome (SIDS) is increased by maternal smoking during pregnancy. Although fewer in number, studies also have found that prenatal exposure to alcohol, especially in the context of heavy drinking, increases risk for SIDS. There are, however, no large prospective studies designed to assess these risks and the potential interaction between smoking and alcohol, or to elucidate specific patterns of timing and amount of exposure that confer greatest risk.

 Added value of this study

This report describes an international collaborative observational study conducted across populations known to be at high risk for infant mortality and exposure to drinking and smoking during pregnancy. The objective of the investigation was to determine associations between prenatal alcohol and cigarette tobacco use and the risk of SIDS. The study, initiated in 2007, was large with approximately 12,000 pregnancies, prospective in design, employed detailed characterization of exposures, and employed rigorous adjudication of every infant death by a multi-disciplinary team. To our knowledge, it is the first to formally explore the association between the dual role of prenatal alcohol and cigarette use and the risk of SIDS. As a first step, group-based trajectory modeling was used to assign individual pregnancies to exposure groups, incorporating quantity, frequency, and timing of prenatal exposure. Second, baseline confounding was controlled by propensity scores developed for each category of exposure. Through detailed prospective collection of exposure information during pregnancy and adjustment for confounding factors, data from diverse populations and regions were combined to investigate the relationship between prenatal alcohol and tobacco use and the risk of SIDS.

 Implications of all the available evidence

This study reveals the risk of SIDS, as compared to known causes of death, is nearly 12-fold greater in pregnancies with combined exposure to smoking and alcohol that continued beyond the first trimester. These findings are particularly relevant since alcohol and tobacco use often co-occur. These data provide strong support for the public heath message that prenatal drinking and smoking are among the most prevalent modifiable risk factors for adverse outcomes.