Ethics approval and consent to participate
Study approval statement: This randomized controlled prospective study was carried out at the neonatal intensive care units (NICUs) of Asan Medical Center (Seoul, South Korea) and Haeundae Paik Hospital (Busan, South Korea) after obtaining approval by the respective institutional review boards (Asan Medical Center, #2015-0367; Haeundae Paik Hospital, #129792-2015-039). All subjects have given their written informed consent.