Late preterm infants contribute to significant neonatal intensive care unit health care resource utilization because of their sheer numbers. Determinants of the length of hospitalization (LOH) in this population are understudied. Gestational age (GA) is used most commonly as a predictor for LOH but there are many limitations including inaccurate dating and morbidities of prematurity which at least partly related to neurophysiological immaturity. The latter can be assessed by amplitude integrated electroencephalogram (aEEG, a simplified 5 lead EEG), and possibly by heart rate variability (HRV) and respiratory variability (RV). All 3 are non-invasive tests that can be done at the bedside. Our study hypothesis is to determine if neurophysiologic maturation as assessed by aEEG, HRV and RV within 24-96 hours following birth improves the correlation between gestational age and length of hospitalization compared to gestational age alone.

Inclusion Criteria:

• Gestational age of 340-346 weeks by Obstetric criteria (presence of a sure LMP or sonogram performed in the first trimester, or agreement between LMP and a sonogram performed between the first trimester and 20 weeks)
• Admitted to a NICU of a participating institution
• Post-natal age less than 96 hours

Exclusion Criteria:

• Major congenital anomaly/genetic anomaly
• Growth restriction (birth weight < 10%, Fenton growth curves)
• Unsure obstetric dating (e.g., absence of a sure LMP without a sonogram, earliest sonogram performed after 20 weeks without a sure LMP, or discrepancy between LMP and sonogram)
• Exposure to medications within the preceding 12 hrs which may affect CNS function (e.g., fentanyl, morphine, midazolam)
• Neonatal seizures
• Neonatal abstinence syndrome secondary to in-utero exposure to narcotics, methadone etc, or at high risk for development of abstinence
• Hypoxia-ischemia defined as the combination of fetal acidemia (cord gas or blood gas within 1 hour of birth: pH ≤ 7.15 or BE ≥ -10mEq/L), need for resuscitation at birth (PPV ± chest compressions or medications), and evidence of encephalopathy (Stage 1, 2 or 3 Sarnat). Stage 1 encephalopathy will be defined based on the level of consciousness which is characterized by a hyper-alert state, apparent alertness, and irritability. In the absence of a cord or early post-natal blood gas, there must be a history of a perinatal event which may have compromised oxygenation or blood flow to the fetus.
• Infants who are expected to be on mechanical (via an endotracheal tube) or high frequency ventilation for the first 96 hours after birth.
• Inability to obtain the informed consent

Neonatal intensive care unit Newborn nursery