Funding for this research was provided by:
China Postdoctoral Science Foundation (No.2019M650773)
National Key Research and Development Program of China (No.2016YFC1301500)
Hebei Provincial Health and Family Planning Commission (No.20181258 and 20181264)
Received: 5 May 2020
Accepted: 26 October 2020
First Online: 29 October 2020
Ethics approval and consent to participate
: All protocols were approved by the Institutional Review Board of Beijing Tiantan Hospital. The appropriate permissions to access the patient database which provided the data for our study were granted by Beijing Tiantan Hospital.
: Not applicable.
: The authors have no financial conflicts of interest.