Funding for this research was provided by:
National Natural Science Foundation of China (81872685)
Natural Science Foundation of Hainan Province (2017JJ3215)
Key Laboratory of Environmental Pollution Monitoring and Disease Control, Guizhou Medical University (GMU-2017-HJZ-05)
Text and Data Mining valid from 2019-09-04
Received: 25 April 2019
Accepted: 30 August 2019
First Online: 4 September 2019
Ethics approval and consent to participate
: This study was reviewed by the Ethical and Confidentiality Committee of Central-South University (Reference XYGW-2016-01, approved on 3rd Mar 2016) and institution review boards (IRB) from the Liuyang Municipal Hospital of Maternal and Child Health. Written consent has been signed by all participants. All personal information has been recoded with initials or numbers which guaranteed no information of the participants can be identified in data analysis.
: Not applicable.
: The authors declare that they have no conflicting interests.