Funding for this research was provided by:
National Natural Science Foundation of China (81671477)
Beijing Municipal Science and Technology Commission (Z161100000516160)
National Key Research and Development Program of China (2016YFC1000304)
Received: 16 July 2020
Accepted: 29 September 2020
First Online: 8 October 2020
Ethics approval and consent to participate
: The study was approved by the Ethics Committee of Beijing Obstetrics and Gynecology Hospital (2012-KY-012, 2016-KY-066). Written informed consent was obtained from all participants. All procedures were performed in compliance with the Declaration of Helsinki.
: Not applicable.
: The authors declare that they have no competing interests.