1. Division of Neonatology, Center of Maternal-Fetal, Neonatal and Reproductive Medicine, National Center for Child Health and Development, Tokyo, Japan
2. Division of Pediatrics and Perinatology, Tottori University Faculty of Medicine, Yonago, Japan
3. Department of Pediatrics, Kyorin University School of Medicine, Tokyo, Japan
4. Department of Social Medicine, Research Institute, National Center for Child Health and Development, Tokyo, Japan