Study population characteristics.
infection, NEC, congenital anomalies, neurological problems
INFECTION, NECROTIZING ENTEROCOLITIS

Healthy in this study is defined as babies in room air, not requiring respiratory support such as high flow nasal canula (HFNC), continuous positive airway pressure (CPAP), Nasal intermittent positive pressure ventilation (NIPPV), conventional mechanical ventilation (CMV), no evidence of major congenital anomalies, neurological problems, necrotizing enterocolitis (NEC) or infection. The reason baby is admitted in the NICU will be recorded.