1. Department of Gynecology and Obstetrics, Peking Union Medical College Hospital, Peking Union Medical College, Beijing, People’s Republic of China;
2. Department of Epidemiology and Statistics, Institute of Basic Medical Sciences, Chinese Academy of Medical Science and School of Basic Medicine, Peking Union Medical College, Beijing, People’s Republic of China;
3. Department of Gynecology and Obstetrics, Children’s Hospital of Shanxi Province, Shanxi, People’s Republic of China;
4. Department of Gynecology and Obstetrics, Maternal and Child Health Hospital of Wuxi, Jiangsu, People’s Republic of China;
5. Department of Gynecology and Obstetrics, Maternal and Child Health Hospital of Gansu Province, Lanzhou, People’s Republic of China;
6. Department of Gynecology and Obstetrics, Maternal and Child Health Hospital of Foshan, Guangdong, People’s Republic of China;
7. Department of Gynecology and Obstetrics, Maternal and Child Health Hospital of Guiyang, Guizhou, People’s Republic of China;
8. Department of Gynecology and Obstetrics, ShengJing Hospital of China Medical University, Shenyang, People’s Republic of China