1 Department of Orthopedics, West China Hospital, Sichuan University, Chengdu, Sichuan, People's Republic of China.
2 Department of Gynecology and Obstetrics, West China Second University Hospital, Sichuan University, Chengdu, Sichuan, People's Republic of China.
3 Key Laboratory of Birth Defects and Related Diseases of Women and Children (Sichuan University), Ministry of Education, Chengdu, People's Republic of China.
4 Department of Epidemiology and Health Statistics, West China School of Public Health, Sichuan University, Chengdu, Sichuan, People's Republic of China.