1. Department of Obstetrics and Gynecology, Seoul National University College of Medicine, Seoul, Korea.
2. Department of Obstetrics and Gynecology, SMG-SNU Boramae Medical Center, Seoul, Korea.
3. Department of Pediatrics, SMG-SNU Boramae Medical Center, Seoul, Korea.
4. Department of Radiology, SMG-SNU Boramae Medical Center, Seoul, Korea.