1. Research Center of Clinical Epidemiology, Peking University Third Hospital, Beijing, China
2. Department of Epidemiology and Biostatistics, School of Public Health, Peking University, Beijing, China
3. Department of Obstetrics, Tongzhou Maternal and Child Health Hospital, Beijing, China
4. Department of Obstetrics, The Second Affiliated Hospital of Kunming Medical University, Kunming, Yunnan Province, China
5. Department of Obstetrics, Qianjiang Maternal and Child Health Hospital, Qianjiang City, Hubei Province, China
6. Department of Obstetrics, Qianjiang Central Hospital, Qianjiang City, Hubei Province, China
7. Department of Obstetrics, Qujing Maternal and Child Health Hospital, Qujing City, Yunnan Province, China
8. Department of Obstetrics, Shexian Maternal and Child Health Hospital, Shexian City, Hebei Province, China
9. National Health Commission Key Laboratory of Reproductive Health, Peking University Health Science Center, Beijing, China