1. Department of Obstetrics and Gynecology, Sungkyunkwan University School of Medicine, Seoul, Korea.
2. Department of Obstetrics and Gynecology, Hallym University College of Medicine, Anyang, Korea.
3. Department of Obstetrics and Gynecology, Hanyang University School of Medicine, Seoul, Korea.
4. Department of Obstetrics and Gynecology, Chung-Ang University College of Medicine, Seoul, Korea.
5. Department of Obstetrics and Gynecology, Seoul National University College of Medicine, Seoul, Korea.
6. The Institute of Reproductive Medicine and Population, Medical Research Center, Seoul National University College of Medicine, Seoul, Korea.