**Author details**

Nguyen Thi Trang\* and Vu Thi Huyen Hanoi Medical University, Hanoi, Vietnam

\*Address all correspondence to: trangnguyen@hmu.edu..vn

© 2018 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.
