Funding for this research was provided by:
National Natural Science Foundation of China (81672831, 81471038)
the special research grant for non-profit public service from the National Health and Family Planning Commission (201502011)
Received: 4 May 2019
Accepted: 18 July 2019
First Online: 24 July 2019
Ethics approval and consent to participate
: The study was approved by the ethics committee of the Changhai Hospital Clinical Research Ethics Committee. Written informed consent was obtained before the data collection and analysis.
: Not applicable.
: The authors declare that they have no competing interests.