1. Dream Foret Obstetrics and Gynecology, Jeju, Korea.
2. Department of Obstetrics and Gynecology, Severance Hospital, Yonsei University College of Medicine, Seoul, Korea.
3. Institute of Women’s Life Medical Science, Yonsei University College of Medicine, Seoul, Korea.
4. Department of Obstetrics and Gynecology, Gangnam Severance Hospital, Yonsei University College of Medicine, Seoul, Korea.
5. Department of Statistics, University of Seoul, Seoul, Korea.