The Impact of Hospital Delivery Volumes of Newborns Born Very Preterm on Mortality and Morbidity

Objective

To examine if the annual patient volume of infants born very preterm (VPT, gestational age <32 weeks) at a hospital is associated with neonatal mortality and morbidity.

Study design

We performed an observational, secondary data analysis using a 20-year panel of birth certificates linked to hospital discharge abstracts, including transfers in California, Michigan, Missouri, Oregon, Pennsylvania, and South Carolina from 1996 through 2015. The study included all in-hospital VPT deliveries (n = 208 261). Study outcomes were in-hospital mortality or serious morbidity (intraventricular hemorrhage, necrotizing enterocolitis, retinopathy of prematurity, or bronchopulmonary dysplasia), attributed to the hospital of birth. Poisson regression models estimated the risk-adjusted relative risk (RR) for mortality and serious morbidity across different patient volume categories within a given hospital using hospital fixed effects.

Results

The risk of mortality and serious morbidity for VPT infants increased as the number of infants born VPT at a hospital decreased. Compared with VPT delivery volumes >100 infants per year, the risk of mortality increased when a given hospital had VPT delivery volumes < 60 per year, ranging from a RR of 1.13 (95% C.I. 1.02-1.25) for volumes between 50 to 59 and 1.39 (1.19-1.62) for VPT volumes <10, and the risk of mortality or serious morbidity increased when a given hospital had VPT volumes <100, ranging from a RR of 1.05 (1.02-1.08) for volumes between 90 to 99 and 1.27 (1.19-1.36) for VPT volumes <10.

Conclusions

These results suggest that, for VPT infants, the risk of both mortality and mortality or serious morbidity is increased as the VPT volume within a given hospital declines.