1. Department of Preventive Medicine, Seoul National University College of Medicine, Seoul, Korea.
2. Environmental Health Center, Seoul National University College of Medicine, Seoul, Korea.
3. Department of Statistics, University of Pittsburgh, Pittsburgh, PA, USA.
4. Institute of Environmental Medicine, Seoul National University Medical Research Center, Seoul, Korea.
5. Department of Surgery, Wonkwang University Sanbon Hospital, Gunpo, Korea.
6. Department of Obstetrics and Gynecology, Seoul National University College of Medicine, Seoul, Korea.