Funding for this research was provided by:
National Natural Science Foundation of China (81871133)
Beijing Municipal Administration of Hospitals Clinical Medicine Development (ZYLX201830)
Text and Data Mining valid from 2020-02-29
Received: 10 June 2019
Accepted: 10 February 2020
First Online: 29 February 2020
Ethics approval and consent to participate
: Ethical approval was obtained from the Ethics Committee of the Beijing Obstetrics and Gynecology Hospital, Capital Medical University.
: Not applicable.
: All authors have declared that they have no competing interests.