1. National Research Institute for Family Planning Beijing China
2. National Human Genetic Resource Center Beijing China
3. Graduate School of Peking Union Medical College Beijing China
4. Department of Epidemiology, Fuwai Hospital, National Center for Cardiovascular DiseaseChina Academy of Medical Sciences and Peking Union Medical College Beijing China
5. Institute of Epidemiology and Statistics, School of Public HealthLanzhou University Lanzhou China
6. Department of Maternal and Child HealthNational Health and Family Planning Commission of the PRC Beijing China