1. Department of Obstetrics and Gynecology; National Medical Center; Seoul Korea
2. Department of Obstetrics and Gynecology; Hanyang University College of Medicine; Seoul Korea
3. Department of Obstetrics and Gynecology; Kangbuk Samsung Hospital; Sungkyunkwan University School of Medicine; Seoul Korea
4. Park's Obstetrics and Gynecology Clinics; Seoul Korea
5. Department of Obstetrics and Gynecology; Guro Hospital, College of Medicine; Korea University; Seoul Korea
6. Maria Fertility Hospital; Seoul Korea