So-called “near-term” infants, born between 34 and 36 6/7 completed weeks of gestation, are also referred to as “late-preterm” infants. Whether they are at higher risk than their term counterparts was the subject of this review of birth and death certificate data for infants born in Utah in the years 1999 to 2004. During this period there were 283,975 births of infants whose estimated gestational age (EGA) ranged from 34 to 42 weeks. Early neonatal (first week), neonatal (first 28 days), and infant (first year) mortality rates were calculated for each weekly gestational age cohort from 34 to 42 weeks. Risk ratios for each cohort were estimated using 40 weeks’ gestation as the reference.
Birth defects were the major cause of death for newborn infants of all gestational ages for all 3 (early neonatal, neonatal, infant) mortality periods. Birth defects were most evident as a cause of death in late-preterm infants. Of infants who died in the first year, nearly two-thirds (63%) of 166 late-preterm (34 to 36 6/7 weeks) neonates compared to 43% of those born at an EGA of 37 weeks died of a birth defect. However, higher mortality rates for all 3 periods were still evident for late-preterm infants after excluding those who died of birth defects. In general, infants born at 34–36 weeks’ gestation were likelier than those born at 40 weeks to die within the first year for all reasons except infections and external causes. Mortality rates for infants born at an EGA of 34 to 36 weeks remained significantly higher after excluding deaths from birth defects when 2 further time periods were analyzed: “late neonatal” (days 8–28) and “postneonatal” (days 29–365).
These results are clear evidence that, although birth defects are the leading cause of death in near-term infants, the mortality risk is also increased for nonanomalous near-term infants compared to those born at term.
Departments of Pediatrics and Internal Medicine and the Intermountain Consortium for Child Health Services Research, University of Utah School of Medicine, Salt Lake City, Utah