a Authors contributed equally.
* Correspondence to:
Hongbo Qi (Address: Department of Obstetrics, The First Affiliated Hospital of Chongqing Medical University, No. 1 Youyi Road, Yuzhong District, Chongqing 400016, China. E-mail: qihongbocy@gmail.com. Telephone: +86 13808376116);
Xin Luo (Address: Department of Obstetrics, The First Affiliated Hospital of Chongqing Medical University, No. 1 Youyi Road, Yuzhong District, Chongqing 400016, China. E-mail: lxcqmu@outlook.com. Telephone: +86 15826109160)
Manuscript word count: 3550
Abstract word count: 249