1. Graduate School of Peking Union Medical College, Beijing, China.
2. Center for Genetics, National Research Institute for Family Planning, Beijing, China.
3. Department of Orthopedic Trauma, Tianjin Hospital, Tianjin, China.
4. Tianjin and Huabei Oil Field Hospital, Hebei, China.
5. World Health Organization Collaborating Centre for Research in Human Reproduction, Beijing, China.