Xuyan Dong, Department of Obstetrics, Huangshi Maternity & Children's Health Hospital, Edong Healthcare Group, Women's & Children's Hospital Affiliated to Hubei Polytechnic University, Xianning 435003, Hubei, P.R. China. Hongjun Li, Department of Obstetrics, Xiaogan xiaonan district maternal and child care service center, Xiaogan 432100, Hubei, P.R. China. Tianjiao Zhu Department of Obstetrics, Xianning Central Hospital, The First Affiliated Hospital of Hubei University of Science and Technology, Xianning 431000, Hubei, P.R. China.