Funding for this research was provided by:
Natural Science Foundation of Liaoning Province (2015020549)
Dalian Municipal Health and Family Planning Project (1711014)
National Natural Science Foundation of China (81300985)
Article History
Received: 22 January 2018
Revised: 27 June 2018
Accepted: 6 July 2018
First Online: 12 July 2018
Compliance with Ethical Standards
:
: The authors declare that they have no conflict of interest.