1 National Human Genetic Resources Center, National Research Institute for Family Planning, Beijing, 100081, People's Republic of China.
2 Prenatal Diagnosis Center, Shijiazhuang Obstetrics and Gynecology Hospital, Hebei Province, Shijiazhuang, 050011, People's Republic of China.
3 Genetic Center, National Research Institute for Family Planning, Beijing, 100081, People's Republic of China.
4 Department of Obstetrics, Shijiazhuang Obstetrics and Gynecology Hospital, Hebei Province, No. 206, East Zhongshan Road, Shijiazhuang, 050011, People's Republic of China. chgr2013@163.com.