Peking University - Department of Maternal and Child Health, National Research Institute for Family Planning, Harvard University - Department of Epidemiology, Johns Hopkins University - Department of Epidemiology, Government of the People's Republic of China - National Health and Family Planning Commission, Government of the People's Republic of China - National Health and Family Planning Commission, Johns Hopkins University - Department of Health Policy and Management, Johns Hopkins University - Department of Epidemiology, Peking University - Department of Maternal and Child Health, Chinese Academy of Medical Sciences - National Research Institute for Family Planning, National Research Institute for Family Planning, Peking University - Department of Maternal and Child Health and National Research Institute for Family Planning