Background Sudden infant death syndrome (SIDS) is the leading cause of postneonatal death in the United States. The rate of SIDS has decreased following the back-to-sleep campaign in the mid-1990s. However, the rate of preterm births is increasing. As of 1998 in the United States, 12% of births were preterm. Analysts have repeatedly observed that preterm birth increases the risk of SIDS, with the magnitude of the risk increasing as gestational length decreases. In light of the changing epidemiology of both SIDS and preterm births, understanding the relationship between preterm birth and SIDS and identifying the impact of length of gestation on age at death from SIDS are critical. The purpose of this study is to describe the relationship between length of gestation and age at death from SIDS in a recent birth cohort.
Design/Methods The study cohort included all singleton, live infants born to US residents from 1996 through 1998. National linked infant birth and death files provided data for the analysis. We used multivariable linear regression with mean (standard deviation) age of SIDS death as the outcome and length of gestation as the exposure of interest controlling for these potential confounders: maternal race/ethnicity, education, age, marital status, initiation of prenatal care, smoking, alcohol use, diabetes, hypertension, parity, infant gender, region of birth, and fetal growth. The referent gestational length was 40-41 weeks.
Results A total of 8,199 babies died from SIDS, yielding a rate of 0.72 per 1000 live births. Among the 1,112,570 infants born at < 37 weeks gestation, 1,682 died from SIDS, yielding a rate of 1.51 per 1000 live births. After adjusting for the potential confounders, infants 22-27 weeks and 28-32 weeks died at mean ages of 20.5 (0.8) weeks and 15.8 (0.5) weeks after birth, respectively (22-27 v. 40-41 and 28-32 v. 40-41: p < .001). Term infants (40-41 weeks) died from SIDS at an adjusted mean age of 14.0 (0.6) weeks. The mean age of death for infants 33-35, 36-37, and 38-39 weeks did not differ significantly from that of term infants. The mean age of SIDS death for postterm infants 42-44 weeks was 13.4 (0.4) weeks (42-44 v. 40-41: p = .14).
Conclusions Preterm delivery continues to be an important risk factor for SIDS. With increasing gestational age, the mean age of SIDS death declines considerably. We found a statistically significant difference of 4-6 weeks between age of death for preterm and term infants. Clinicians caring for premature infants must provide SIDS prevention counseling before and during peak risk, which changes with gestational length.
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