Acknowledgements
This study was supported by the Science and Technology Program of Shandong Province, China (No. 2012YD18066), the Health and Family Planning Commission of Shandong Province, China (No. 9, 2013), the Science and Technology Management Bureau of Jining City, China (No. 2012jnnk03), and the PhD Startup funds from the Affiliated Hospital of Jining Medical University (2016-BS-001).
Potential conflict of interest
Disclosure forms provided by the authors are available with the full text of this article online at http://dx.doi.org/10.1080/10428194.2017.1312378.