- Correspondence to Professor Lin-Hong Wang, Maternal and Child Healthcare Center, Chinese Center for Disease Control and Prevention, Beijing 100081, China; ; Dr Lei Zhang, Department of Epidemiology and Biostatistics, School of Public Health, Xi'an Jiaotong University, Xi'an, Shaanxi, China;
- Received April 2, 2018
- Revised August 10, 2018
- Accepted September 18, 2018
- First published October 18, 2018.
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