1. Nursing Department, Baoji Maternal and Child Health Hospital, Baoji, China
2. No. 986 Air Force Hospital of PLA, Xi’an, China
3. Department of Obstetrics and Gynecology, the First Affiliated Hospital of Xi’an Jiaotong University, Xi’an, China
4. School of Life Science and Technology, Xi’an Jiaotong University, Xi’an, China