Funding for this research was provided by:
Shanghai Municipal Population and Family Planning Commission (GWIV-26)
Text and Data Mining valid from 2020-02-14
Received: 12 September 2019
Accepted: 7 January 2020
First Online: 14 February 2020
Ethics approval and consent to participate
: An ethical approval was obtained from the Ethics Review Board of the Xinhua hospital, Shanghai Jiao Tong University School of Medicine and other participating hospitals. Conventional informed consent was not necessary in this study.
: Not applicable.
: The authors declare that they have no competing interests.