1. Department of Obstetrics and GynecologyUniversity of Ulsan College of Medicine, Asan Medical Center Seoul Republic of Korea
2. Division of Neonatology, Department of PediatricsUniversity of Ulsan College of Medicine, Asan Medical Center Seoul Republic of Korea
3. Department of RadiologyUniversity of Ulsan College of Medicine, Asan Medical Center Seoul Republic of Korea
4. Department of Clinical Epidemiology and BiostatisticsUniversity of Ulsan College of Medicine, Asan Medical Center Seoul Republic of Korea