P2.H150: Trends in Mortality and Racial Disparities in Infants Under 500 Grams Birth Weight in the United States, 2005-2019

Background: Advances in medicine have led to improved survival for preterm infants but population-based mortality data is scarce. The survival rate of preterm infants with birthweight (BW) < 500 gm has been estimated as 21-80% but little is known about mortality trends in this population. There are racial disparities in infant mortality rate (IMR) but there is paucity of data on this in infants with BW < 500 gm. We examined the trends and differences in mortality among racial groups in preterm infants with BW < 500 gm in the United States (US) from 2005 – 2019.

Methods: This was a retrospective serial cross-sectional study of the linked birth / infant death records from the CDC’s Wide-ranging Online Data for Epidemiologic Research (WONDER) for the years 2005 through 2019. Infants with gestational age (GA) 22-28 wks, BW < 500 gm, and deaths up to 1 yr of age were included. IMR was calculated as deaths per 1,000 live births for each GA and year, and further stratified by maternal race. We evaluated trends with Joinpoint regression and IMR trends were reported using average annual percentage change (AAPC) with 95% confidence intervals (CI). Differences in IMR among racial groups were ascertained using ANOVA with post hoc Tukey's Honestly Significant Difference (HSD). P-value < 0.05 was considered significant.

Results: Among over 60 million live births in the US, 43,500 births met the inclusion criteria with an average IMR (per 1,000) of 788. Of these births the racial breakdown was 15% Hispanic, 37% Non-Hispanic Black (NHB), and 37% Non-Hispanic White (NHW). IMR was inversely related to GA (figure 1A). From 2005-2019, the overall IMR decreased from 817 to 763 among all races (Figure 1B) with an AAPC of -0.59% (CI, -0.8, -0.4). The decline in IMR was significant for GA 23, 24, 25, and 27. The IMR decreased in NHB (790 to 731; AAPC: -0.6%, CI, -0.8, -0.34) and in NHW (829 to 787; AAPC: -0.25%, CI, -0.45, -0.05), but no significant change among Hispanic infants (848 to 786; AAPC: -0.2%, CI: -0.9, 0.4). The IMR was significantly different among the races/ethnicities (NHB 768, NHW 806, and Hispanic 826). These differences were significant (NHW vs NHB; P= 0.001; NHW vs Hispanic: P= 0.04; NHB vs Hispanic, P= 0.001).

Conclusion: The IMR among infants 22-28 weeks GA and with BW < 500 gm declined significantly from 2005-2019. The decline was uneven among racial groups with no significant trend in the hispanic population. This updated data may support clinicians in counseling parents, and policy makers in understanding national trends in mortality rate to inform research and policies.