LIU Jing
Graduate School of Peking Union Medical College, Beijing 100730, China;National Research Institute for Family Planning, Beijing 100081, ChinaHE Jia-ling
National Research Institute for Family Planning, Beijing 100081, ChinaBAO Guo
National Research Institute for Family Planning, Beijing 100081, ChinaLI Nan
National Research Institute for Family Planning, Beijing 100081, ChinaWANG Tian-qi
National Research Institute for Family Planning, Beijing 100081, ChinaZHANG Chang-yong
National Research Institute for Family Planning, Beijing 100081, ChinaSUN De-ming
National Research Institute for Family Planning, Beijing 100081, China