Cohort selection and the estimation of racial disparity in mortality of extremely preterm neonates.

BACKGROUND

Racial disparities in preterm neonatal mortality are long-standing. We aimed to assess how cohort selection influences mortality rates and racial disparity estimates.

METHODS

With 2014-2018 California data, we compared neonatal mortality rates among Black and non-Hispanic White very low birth weight (VLBW, <1500 g) or very preterm infants (22-29 weeks gestational age). Relative risks were estimated by different cohort selection criteria. Blinder-Oaxaca decomposition quantified factors contributing to mortality differential.

RESULTS

Depending upon standard selection criteria, mortality ranged from 6.2% (VLBW infants excluding first 12-h deaths) to 16.0% (22-29 weeks' gestation including all deaths). Black observed neonatal mortality was higher than White infants only for delivery room deaths in VLBW infants (5.6 vs 4.2%). With risk adjustment accounting for higher rate of low gestational age, low Apgar score and other factors, White infant mortality increased from 15.9 to 16.6%, while Black infant mortality decreased from 16.7 to 13.7% in the 22-29 weeks cohort. Across varying cohort selection, risk adjusted survival advantage among Black infants ranged from 0.70 (CL 0.61-0.80) to 0.84 (CL 0.76-0.93).

CONCLUSIONS

Standard cohort selection can give markedly different mortality estimates. It is necessary to reduce prematurity rates and perinatal morbidity to improve outcomes for Black infants.

IMPACT

In this population-based observational cohort study that encompassed very low birth weight infant hospitalizations in California, varying standard methods of cohort selection resulted in neonatal mortality ranges from 6.2 to 16.0%. Across all cohorts, the only significant observed Black-White disparity was for delivery room deaths in Very Low Birth Weight births (5.6 vs 4.2%). Across all cohorts, we found a 16-30% survival advantage for Black infants. Cohort selection can result in an almost three-fold difference in estimated mortality but did not have a meaningful impact on observed or adjusted differences in neonatal mortality outcomes by race and ethnicity.