**Conflict of interest**

We declare no conflict of interest.

### **Author details**

Jinlin Liu1 , Yvon Englert<sup>2</sup> and Wei-Hong Zhang2,3,4\*

1 Research Center for the Belt and Road Health Policy and Health Technology Assessment, Xi'an Jiaotong University, Xi'an, China

2 Research Laboratory for Human Reproduction, Faculty of Medicine, School of Public Health, Université Libre de Bruxelles (ULB), Brussels, Belgium

3 International Centre for Reproductive Health (ICRH), Department of Public Health and Primary Care, Ghent University, Ghent, Belgium

4 Research Centre for Public Health, Tsinghua University, Beijing, China

\*Address all correspondence to: weihong.zhang@ugent.be

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
