Bias in comparisons of mortality among very preterm births: A cohort study

Abstract

Background Several studies of prenatal determinants and neonatal morbidity and mortality among very preterm births have resulted in unexpected and paradoxical findings. We aimed to compare perinatal death rates among cohorts of very preterm births (24–31 weeks) with rates among all births in these groups (≥24 weeks), using births-based and fetuses-at-risk formulations. Methods We conducted a cohort study of singleton live births and stillbirths ≥24 weeks’ gestation using population-based data from the United States and Canada (2006–2015). We contrasted rates of perinatal death between women with or without hypertensive disorders, between maternal races, and between births in Canada vs the United States. Results Births-based perinatal death rates at 24–31 weeks were lower among hypertensive than among non-hypertensive women (rate ratio [RR] 0.67, 95% CI 0.65–0.68), among Black mothers compared with White mothers (RR 0.94, 95%CI 0.92–0.95) and among births in the United States compared with Canada (RR 0.74, 95%CI 0.71–0.75). However, overall (≥24 weeks) perinatal death rates were higher among births to hypertensive vs non-hypertensive women (RR 2.14, 95%CI 2.10–2.17), Black vs White mothers (RR 1.86, 95%CI 184–1.88;) and births in the United States vs Canada (RR 1.08, 95%CI 1.05–1.10), as were perinatal death rates based on fetuses-at-risk at 24–31 weeks (RR for hypertensive disorders: 2.58, 95%CI 2.53–2.63; RR for Black vs White ethnicity: 2.29, 95%CI 2.25–2.32; RR for United States vs Canada: 1.27, 95%CI 1.22–1.30). Conclusion Studies of prenatal risk factors and between-centre or between-country comparisons of perinatal mortality bias causal inferences when restricted to truncated cohorts of very preterm births.

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

“…Although the fetus at risk approach and its modification is not universally accepted, 28 it focuses attention on the notion that burden to the clinician, as well as the family, is dependent upon both rate and volume. 29 Similar findings were reported by Wu et al who state that this paradox (the Black disadvantage estimated by the fetus at risk approach) seen when GA specific neonatal mortality rate is stratified by risk factors such as race, “may be explained if more neonates without congenital anomalies are born at earlier GA among Black vs White mothers.” 30 Our study of very preterm infants is limited to California, which may have population and healthcare-specific differences from other states. For example, our 2020 infant mortality of 3.92 is one of the lowest in the country.…”

Birth-Based vs Fetuses-at-Risk Approaches for Assessing Neonatal Mortality Rate by Race

“…By only counting PTB in the denominator for extreme and very PTB categories, the birth-based approach does not control for race-related differences in PTB rate, which distort race-related NMR. Since using a birth-based approach may mask racial disparities, a FAR approach is recommended for GA-specific perinatal research …”

“…Since using a birth-based approach may mask racial disparities, a FAR approach is recommended for GA-specific perinatal research. 2,6 Bohao Wu, MPhil Sarah Taylor, PhD Veronika Shabanova, PhD Nicola L. Hawley, PhD…”

The Relationship Between Regional Growth in Neonatal Intensive Care Capacity and Perinatal Risk

“…Maternal low educational attainment is an indicator of socioeconomic status and an indirect indicator of newborn health risk. At a population level, maternal self-identification as Black indicates a risk of systemic racism and personal discrimination strongly associated with poorer health in reproductive years, difficulty in accessing good health care, and worse maternal and fetal/newborn outcomes 21,22 . The expectation is that these measures indicate an increased population newborn health risk, and hence an overall higher need for NICU care and capacity.…”

“…At a population level, maternal self-identification as Black indicates a risk of systemic racism and personal discrimination strongly associated with poorer health in reproductive years, difficulty in accessing good health care, and worse maternal and fetal/newborn outcomes. 21 , 22 The expectation is that these measures indicate an increased population newborn health risk, and hence an overall higher need for NICU care and capacity. Six additional maternal and newborn characteristics that are associated with neonatal outcomes are included in secondary analyses (Supplemental Table 1, Supplemental Digital Content 1, http://links.lww.com/MLR/C676 ).…”