Risk of Infant Mortality by Race/Ethnicity among Preterm Infants at Different Gestational Ages

Abstract

Background: Preterm infants born at earlier gestational ages are at greater risk for mortality compared to late-preterm or term infants. There is a strong association between infant mortality and an infant's race/ethnicity at all gestational ages. This study assessed infant mortality relative to race/ethnicity among preterm infants in three gestational age groups. A secondary analysis evaluated mortality by race/ethnicity relative to the timing of death (neonatal vs. post-neonatal mortality). Methods: Washington State linked Birth and Death Certificates for infants born between 1984 and 2009 were used to identify cases, defined as live-born infants who died within the first 364 days, and controls, defined as infants who did not die in the first year. Controls were matched to cases on gestational age and year of birth. Subjects were stratified by gestational age at birth into three groups: 24-27 weeks, 28-32 weeks, and 33-36 weeks. Logistic regression was used to calculate odds ratios for mortality by race/ethnicity within each gestational age group. Results: Among infants born at 24-27 weeks and 28-32 weeks, Black infants were less likely to die in the first year compared to White infants (OR: 0.69, 95% CI: 0.56, 0.86 and OR: 0.69, 95% CI: 0.53, 0.91 respectively). Hispanic and Asian/Pacific Islander infants born at 33-36 weeks were less likely to experience infant mortality compared with White infants (OR: 0.72, 95% CI: 0.56, 0.91 and OR: 0.69, 95% CI: 0.52, 0.91, respectively). Evaluation of timing of death indicated that Black infants born at 24-27 weeks were more likely to experience post-neonatal mortality relative to neonatal mortality, compared with White infants in that gestational age range (OR: 2.15, 95% CI: 1.46, 3.17). Hispanic infants born at 33-36 weeks were less likely to experience post-neonatal mortality relative to neonatal mortality compared with White infants (OR: 0.57, 95% CI: 037, 0.87). Conclusions: The results of this study suggest that interventions to prevent infant mortality among preterm infants must consider both the gestational age at birth and the race/ethnicity of the infant. Infants at increased risk of post-neonatal mortality require continued support and services following hospital discharge.