Hospital volume and neonatal mortality among very low birth weight infants

Very low birth weight infants (< 1500 g) are at increased mortality risk. Data on the impact of NICU volume are sparse, in comparison with those on the level of care. We hypothesized that neonatal mortality would be higher in small NICUs (< 36 very low birth weight admissions per year) than in large NICUs, with adjustment for volume of the delivery unit.

We analyzed population-based data from a quality assurance program in Lower Saxony (Germany). Perinatal data for almost all very low birth weight infants born in 1991 to 1999 (n = 7745) were available. Analyses were restricted to infants born at 24 to 30 weeks (n = 4379). Data validation procedures, univariate data analyses, and logistic regression models based on general estimating equations were performed.

Neonatal mortality among infants admitted to NICUs was 12.2% in small NICUs and 10.2% in large NICUs. The mortality rate in small NICUs was increased significantly. Compared with infants from large delivery hospitals (> 1000 births per year) and large NICUs, the adjusted odds ratio was 1.94 for neonates for whom both units were small, 1.75 for those from large delivery units but small neonatal units, and 1.16 for those for whom only the NICU was large. Stratification according to gestational age revealed the greatest impact on mortality for infants of < 29 weeks.

Results suggest that creating larger perinatal centers may improve perinatal health care. The volume of the NICU was associated more strongly with 28-day mortality than was the volume of the delivery hospital, and it had the largest impact on survival for infants of < 29 weeks.