1. Department of Obstetrics and Gynecology, Samsung Cheil Hospital, Sungkyunkwan University, Seoul, Korea.
2. Department of Obstetrics and Gynecology, Samsung Medical Center, Sungkyunkwan University, Seoul, Korea.
3. Department of Obstetrics and Gynecology, Asan Medical Center, University of Ulsan, Seoul, Korea.
4. Department of Obstetrics and Gynecology, Cheil Women's Clinic, Seoul, Korea.
5. Department of Obstetrics and Gynecology, Ilsan Cheil Hospital, Ilsan, Korea.
6. Department of Obstetrics and Gynecology, Bombit Women's Hospital, Seoul, Korea.
7. Department of Obstetrics and Gynecology, Ewha Women's University Mokdong Hospital, Seoul, Korea.
8. Institute for Occupation and Environmental Health, Seoul, Korea.
9. Department of Obstetrics and Gynecology, Kangnam St. Mary's Hospital, The Catholic University of Korea, Seoul, Korea.
10. Department of Obstetrics and Gynecology, Sanggye Baik Hospital, Inje University, Seoul, Korea.
11. Department of Obstetrics and Gynecology, Seoul National University Hospital, Seoul, Korea.