1. Department of Obstetrics and Gynecology, National Taiwan University Hospital Yunlin Branch, Douliu, Taiwan
2. Department of Obstetrics and Gynecology, National Taiwan University Hospital, Taipei, Taiwan
3. Institute of Statistical Science, Academia Sinica, Taipei, Taiwan
4. College of Medicine, National Taiwan University, Taipei, Taiwan
5. Graduate Institute of Epidemiology and Preventive Medicine, National Taiwan University, Taipei, Taiwan