Moderately preterm infants (30–3467 weeks' gestational age) represent the largest population of NICU residents. Whether their clinical outcomes are associated with differences in NICU nurse-staffing arrangements has not been assessed. The objective of this study was to test the influence of patient-to-nurse ratios (PNRs) on outcomes of care provided to moderately preterm infants.


Using data from a prospective, multicenter, observational cohort study of 850 moderately preterm infants from 10 NICUs in California and Massachusetts, we tested for associations between PNR and several important clinical outcomes by using multivariate random-effects models. To correct for the influence of NICU size, we dichotomized the sample into those with an average daily census of <20 or ≥20 infants.


Overall, we found few clinically significant associations between PNR and clinical outcomes of care. Mean PNRs were higher in large compared with small NICUs (2.7 vs 2.1; P < .001). In bivariate analyses, an increase in PNR was associated with a slightly higher daily weight gain (5 g/day), greater gestational age at discharge, any intraventricular hemorrhage, and severe retinopathy of prematurity. After controlling for case mix, NICU size, and site of care, an additional patient per nurse was associated with a decrease in daily weight gain by 24%. Other variables were no longer independently associated with PNR.


In this population of moderately preterm infants, the PNR was associated with a decrease in daily weight gain, but was not associated with other measures of quality. In contrast with findings in the adult intensive care literature, measured clinical outcomes were similar across the range of nurse-staffing arrangements among participating NICUs. We conclude that the PNR is not useful for profiling hospitals' quality of care delivery to moderately preterm infants.

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