Funding for this research was provided by:
National Health and Family Planning Commission of the People's Republic of China (WKJ2014-2-011)
Zhejiang Province Public Welfare Technology Application Research Project (2015C33107)
Received: 14 September 2019
Accepted: 22 December 2019
First Online: 6 January 2020
Ethics approval and consent to participate
: The study was approved by human research ethics committee of the second affiliated hospital of Zhejiang University School of Medicine (2018–025). Due to the retrospective observational nature of the study, the Institutional Review Board waived the need for informed consent.
: Not applicable.
: The authors declare that they have no competing interests.