Funding for this research was provided by:
National Natural Science Foundation of China (71774059, 71473098)
Text and Data Mining valid from 2020-05-08
Received: 6 November 2019
Accepted: 23 April 2020
First Online: 8 May 2020
Ethics approval and consent to participate
: This study was approved by the Research Ethics Committee of Tongji Medical College, Huazhong University of Science and Technology (IORG No: IORG0003571). Consent from women whose records were included was not sought because their private information, such as name and identity card information, was not obtained.
: Not applicable.
: The authors declare that they have no competing interests.