Funding for this research was provided by:
Xi’an Jiaotong University (DW080038K0000004)
China Postdoctoral Science Foundation (2015M582678)
Health and Family Planning Commision of Shaanxi Province (2016D091)
Received: 27 December 2017
Accepted: 17 July 2018
First Online: 24 July 2018
Ethics approval and consent to participate
: The study protocol was approved by the Ethical Committee of Xi’an Jiaotong University Health Science Center (No. 2015-639). Written informed consent was obtained from all participants.
: Not applicable.
: The authors declare that they have no competing interests.
: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.