Factor affecting length of stay in late preterm infants: an US national database study.

Objectives: Late preterm infants are the fastest growing segment of the premature infant population in the United States. However, it is not known if demographic and clinical factors can impact the length of hospital stay (LOS) in this population. The objectives of this study are to determine the following: (a) factors associated with a LOS > 3 d and (b) whether there is any difference in risks between infants born at 33-34 versus 35-36 weeks.

Methods: Utilizing the Nationwide Inpatient Sample Database, a de-identified dataset produced by the Healthcare Cost and Utilization Project, analysis of 81 913 infants born at 33-36 weeks from 2007 to 2008 was conducted. LOS outcome was defined as ≤3 and >3 d. Bivariable and multivariable logistic regression was used to evaluate predictors of LOS among this population.

Results: Only 42.7% of infants were discharged home within three days. Factors associated with a LOS > 3 d included gestational age of <35 weeks (RR = 1.63; CI: 1.58-1.68), birth weight of < 2500 g (RR = 1.36; CI: 1.33-1.39), male sex (RR = 1.06; CI: 1.05-1.07), delivery via C-section (RR = 1.46; CI: 1.41-1.51) and multiple gestation (RR = 1.08; 95% CI: 1.06-1.09). Other significant factors included race, birth region, primary insurance payer and clinical complications. In the adjusted interaction model, these variables have more impact on longer LOS in the 35-36 weeks group (p < 0.0001).

Conclusion: Birth region in addition to gestational age, birth weight, gender, mode of delivery, multiple gestation and primary insurance payer affect LOS in late preterm infants. These variables are more critical for the 35-36 week population.