Infant Mortality through the Years

Published - Written by Rena Xu

Prematurity has long been recognized as a major contributor to infant mortality. One in every four infants born extremely prematurely (between 22 and 29 weeks’ gestation) does not survive. A large number die within the first 12 hours after birth, and many more never make it out of the hospital, most commonly dying from a respiratory condition.

Efforts have been made to improve the prognosis for these infants. Neonatal care has evolved in its use of glucocorticoids, antibiotics, surfactant, and ventilation, to name just a few examples of interventions targeting pulmonary-related deaths. Have these changes in practice changed the state of infant mortality?

A study published this week in NEJM looked at the incidence and causes of death among extremely premature infants from 2000 to 2011. The investigators prospectively collected data on over 22,000 extremely premature infants born in one of 25 Neonatal Research Centers. They followed them from birth to 120 days (or to death, discharge, or hospital transfer, if one of these occurred first). If hospitalized for more than 120 days, infants were evaluated for death until 1 year of age.

Roughly one fourth of the infants died during their birth hospitalization (6075 deaths). Over 40% of deaths occurred in the first 12 hours after birth. Earlier gestational age at birth was linked to a worse outcome; infants who died had a mean gestational age a little over 24 weeks, versus 26 weeks in the infants who survived. Their mothers were also less likely to have received prenatal glucocorticoids (62% versus 88%).

Overall, through the years, mortality declined. The number of deaths per 1000 live births was 275 in the 2000-2003 period; 285 in the 2004-2007 period; and 258 in the 2008-2011 period (P=0.003). The study detected significant changes in neonatal care across these periods. There was an increase in the percentage of women receiving any prenatal care, as well as the percentage receiving prenatal glucocorticoids. Use of prenatal antibiotics decreased, while use of high-frequency ventilation increased, more than doubling among the most premature infants.

Trends in cause of mortality also shifted. The number of deaths attributed to respiratory distress syndrome and bronchopulmonary dysplasia decreased from the 2000-2003 period to the 2008-2011 period (from 83 to 68 per 1000 live births). This decrease accounted for more than half the decline in overall mortality. The number of deaths attributed to immaturity, infection, or central nervous system injury also fell. There was, however, an increase in the number of deaths attributed to necrotizing enterocolitis (from 23 to 30 per 1000 live births).

“The increase in mortality attributed to necrotizing enterocolitis may be related to improvements in the early survival of infants who would have otherwise died before they reached the typical postnatal age at which necrotizing enterocolitis occurs,” the authors hypothesized.

While this study was not designed to evaluate causality, it identified an improvement in overall and pulmonary-related mortality among extremely premature infants concurrent with changes in neonatal practice. The authors concluded, “Our findings underscore the continued need to develop and implement strategies for reducing the potentially lethal complications of premature birth.”