Nanjing Medical University - Department of Epidemiology and Biostatistics, Women and Children Branch Hospital of Jiangsu Province Hospital/Jiangsu Women and Children Health Hospital - Department of Group Health, Nanjing Medical University - Department of Maternal, Child and Adolescent Health, Nantong Municipal Maternal and Child Health Hospital, Binhai People's Hospital - Department of Obstetrics and Gynecology, Shuyang Hospital of Traditional Chinese Medicine - Department of Obstetrics and Gynecology, Xinyi People's Hospital - Department of Obstetrics and Gynecology, Yixing People's Hospital - Department of Obstetrics and Gynecology, Guannan People's Hospital - Department of Obstetrics and Gynecology, Shuyang People's Hospital - Department of Obstetrics and Gynecology, Nanjing Medical University - Department of Obstetrics and Gynecology, Nanjing Jiangbei People's Hospital - Department of Obstetrics and Gynecology, Nantong First People's Hospital - Department of Obstetrics and Gynecology, Nantong University - Department of Obstetrics and Gynecology, Nanjing Medical University - State Key Laboratory of Reproductive Medicine, Nanjing Medical University - Department of Epidemiology and Biostatistics, Nanjing Medical University - Department of Epidemiology, Women and Children Branch Hospital of Jiangsu Province Hospital/Jiangsu Women and Children Health Hospital - Department of Group Health, Nanjing Medical University - Department of Epidemiology and Biostatistics, Government of the People's Republic of China - Department of Biliary Tract Surgery I and Nanjing Medical University - State Key Laboratory of Reproductive Medicine