BACKGROUND AND OBJECTIVES: Neonatal intensive care unit (NICU) aggregate service and outcome descriptions focus on high-illness-acuity neonates. We sought to describe the high-level landscape of lower-acuity inborn NICU admissions (LAINAs). METHODS: This cross-sectional study of a nearly three-quarters population sample from 2022 describes 120 California hospitals with inborn NICU admissions. Binary illness acuity stratification was based on high-acuity criteria-admission within 28 days of birth and either birthweight of 1500 g or less, gestation of 31 weeks 6 days or less, or more than 1500 g with at least 1 of the following: death, assisted ventilation for 4 hours or more whether intubated or not, early bacterial sepsis, major surgery requiring anesthesia, acute transport in or out, suspected encephalopathy/perinatal asphyxia, active therapeutic hypothermia, or seizures. Exposure: inborn NICU admission
main outcomes: LAINA categorization, diagnostic categories, patient-days, length of stay. RESULTS: Of 44 330 total NICU admissions, 26 257 (59.2%) were LAINAs and accounted for 31.2% of all NICU patient-days. Mean length of stay for all NICU admissions was 12.9 days, compared with 8.0 days for LAINAs. The most common LAINA diagnostic categories included respiratory distress (43.0%), suspected infection (39.6%), admission policy based only on birthweight/gestational age (30.7%), hyperbilirubinemia (28.9%), and feeding difficulty (25.6%). NICUs varied widely in the diagnostic categories represented. CONCLUSIONS: LAINAs outnumbered high-illness-acuity admissions in most NICUs, accounting for almost a third of NICU patient-days. These findings merit reflection and research on data elements needed to describe service provision and clinical outcome and on preferable hospital settings for clinical management.