1. Antenatal Health Care Department National Center for Women and Children's Health, China CDC Beijing China
2. School of Public Health and Primary Care The Chinese University of Hong Kong Sha Tin Hong Kong
3. Antenatal Health Care Department Maternal and Child Health Hospital of Guangxi, Zhuang Autonomous Region Nanning China
4. Antenatal Health Care Department Yunnan Maternal and Child Health Care Hospital Kunming China
5. The Chinese University of Hong Kong Shenzhen Research Institute Shenzhen China