Effects of a Birth Hospital's Neonatal Intensive Care Unit Level and Annual Volume of Very Low-Birth-Weight Infant Deliveries on Morbidity and Mortality.

IMPORTANCE: The annual volume of deliveries of very low-birth-weight (VLBW) infants has a greater effect on mortality risk than does neonatal intensive care unit (NICU) level. The differential effect of these hospital factors on morbidity among VLBW infants is uncertain.
OBJECTIVE: To assess the independent effects of a birth hospital's annual volume of VLBW infant deliveries and NICU level on the risk of several neonatal morbidities and morbidity-mortality composite outcomes that are predictive of future neurocognitive development. DESIGN, SETTING, AND PARTICIPANTS: Retrospective, population-based cohort study (performed in 2014) of all VLBW infants without severe congenital anomalies delivered in all hospitals in California, Missouri, and Pennsylvania between January 1, 1999, and December 31, 2009 (N = 72,431). Risk-adjusted odds ratios and risk-adjusted probabilities were determined by logistic regression. MAIN OUTCOMES AND MEASURES: The primary study outcomes were the individual composites of death or bronchopulmonary dysplasia, necrotizing enterocolitis, retinopathy of prematurity, and severe intraventricular hemorrhage.
RESULTS: Among the 72,431 VLBW infants in the present study, birth at a hospital with 10 or less deliveries of VLBW infants per year was associated with the highest risk-adjusted probability of death (15.3% [95% CI, 14.4%-16.3%]), death or severe intraventricular hemorrhage (17.5% [95% CI, 16.5%-18.6%]), and death or necrotizing enterocolitis (19.3% [95% CI, 18.1%-20.4%]). These complications were also more common among infants born at hospitals with a level I or II NICU compared with infants delivered at hospitals with a level IIIB/C NICU. The risk-adjusted probability of death or retinopathy of prematurity was highest among infants born at hospitals with a level IIIB/C NICU and lowest among infants born at hospitals with a level IIIA NICU. When the effects of NICU level and annual volume of VLBW infant deliveries were evaluated simultaneously, the annual volume of deliveries was the stronger contributor to the risk of death, death or severe intraventricular hemorrhage, and death or necrotizing enterocolitis. CONCLUSIONS AND RELEVANCE: The risk of death or severe intraventricular hemorrhage and death or necrotizing enterocolitis was lowest among infants born in hospitals that had both a high volume of VLBW infant deliveries and a high-level NICU. Antenatal transfer of high-risk pregnancies to these hospitals may reduce mortality and improve outcomes.