1. In a large cohort of infants with birth defects, the population proportion (PAF) of preterm birth for risk of neonatal death was 51.7%.
2. PAF varied significantly by specific birth defect, from 26.1% for hypoplastic left heart syndrome to 76.2% for anotia/microtia.
Evidence Rating Level: 2 (good)
Course of study: Birth defects are associated with an increased risk of neonatal mortality, defined as death within 28 days of birth. Population fraction (PAF) is a useful metric that assesses the role that a given exposure plays in developing a given outcome. In this study, the PAF of prematurity was calculated for neonatal mortality in a large cohort of approximately 169,000 infants with birth defects. 24.2% of these infants were born prematurely. The PAF of prematurity for neonatal mortality was 51.7% overall in infants with birth defects, indicating that about half of the mortality risk was due to prematurity. The PAF for individual birth defects ranged from 26.1% for hypoplastic left heart syndrome to 76.1% for hypospadias and 76.2% for anotia or microtia. In general, more serious birth defects associated with a higher risk of all-cause mortality, including critical heart defects, were associated with a lower PAF of prematurity, while less critical defects were more likely to have a mortality risk from prematurity. This relationship is intuitive but has not been previously reported. Although the overall benefits of preventing preterm birth are well known, this study supports efforts to prevent preterm birth in infants with birth defects to reduce the risk of neonatal mortality.
Click here to read the study in the Journal of Pediatrics
Relevant reading: Etiology and clinical presentation of birth defects: population-based study
Detailed [retrospective cohort]: Infants born alive between 1999 and 2014 after a gestation of 24 weeks or more and who were part of the Texas Birth Defects Registry were included. Infants with anencephaly, chromosomal abnormalities, or diagnosed syndromes were excluded. Multiple birth defects were present in 30.6% of preterm infants compared to 24.1% of newborns. Congenital heart defects were also more common in preterm infants, at 46.7% versus 34.1%. PAF was calculated using the prevalence of neonatal death in the relevant group and the mortality risk ratio between preterm and term infants. The 95% confidence interval (CI) for the PAF in total birth defects was 49.4-54.0%. PAF was 19.2% for all infants born at 24-28 weeks gestation, 13.9% for 28-32 weeks gestation and 18.7% for 32-37 weeks gestation.
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