1 Institute of Reproductive and Child Health, National Health Commission Key Laboratory of Reproductive Health, Peking University Health Science Center, Beijing 100191, China; Office for National Maternal and Child Health Statistics of China, School of Public Health, Peking University Health Science Center, Beijing 100191, China; Department of Epidemiology and Biostatistics, School of Public Health, Peking University Health Science Center, Beijing 100191, China.
2 Department of Obstetrics and Gynecology, Brigham and Women's Hospital, Harvard Medical School, Boston, MA 02115, USA.
3 Office for National Maternal and Child Health Statistics of China, School of Public Health, Peking University Health Science Center, Beijing 100191, China; Department of Child, Adolescent and Women's Health, School of Public Health, Peking University Health Science Center, Beijing 100191, China.
4 Departments of Pediatrics and Environmental Medicine, NYU School of Medicine, NY 100016, USA; Department of Population Health, NYU School of Medicine, NY 100016, USA; NYU Wagner School of Public Service, NY 100012, USA.
5 Department of Obstetrics and Gynecology, Center for Reproductive Medicine, Peking University Third Hospital, Beijing 100191, China; Key Laboratory of Assisted Reproduction, Ministry of Education, Beijing 100191, China; Reproductive Health Research Center of Peking University Health Science Center, Beijing 100191, China. Electronic address: jie.qiao@263.net.
6 Department of Population Health, NYU School of Medicine, NY 100016, USA; NYU Wagner School of Public Service, NY 100012, USA.
7 Institute of Reproductive and Child Health, National Health Commission Key Laboratory of Reproductive Health, Peking University Health Science Center, Beijing 100191, China; Office for National Maternal and Child Health Statistics of China, School of Public Health, Peking University Health Science Center, Beijing 100191, China; Department of Epidemiology and Biostatistics, School of Public Health, Peking University Health Science Center, Beijing 100191, China; Reproductive Health Research Center of Peking University Health Science Center, Beijing 100191, China. Electronic address: liujm@pku.edu.cn.