1. Department of Obstetrics and Gynecology; Keio University School of Medicine; Tokyo Japan
2. The Perinatology Committee of the Japan Society of Obstetrics and Gynecology; Tokyo Japan
3. The Perinatal Research Network Group in Japan; Kyoto Japan
4. Department of Gynecology and Obstetrics; Kyoto University; Kyoto Japan
5. Department of Obstetrics and Gynecology; Faculty of Medicine; Juntendo University; Tokyo Japan