1. Department of Obstetrics, The Haining Maternal and Child Health Hospital, Haining
2. Department of Obstetrics and Gynecology, The First Affiliated Hospital of Guangxi Medical University, Nanning
3. Department of Obstetrics, Changsha Ning Er Maternity Hospital, Changsha
4. Reproductive Medicine Research Center, The First Affiliated Hospital of Guangxi Medical University, Nanning, P. R. China