1. College of Life Science and OceanographyShenzhen University Shenzhen 518060 P. R. China
2. Department of Obstetrics and GynecologyAffiliated Hospital of Guizhou Medical University Guiyang 550004 P. R. China
3. School of Public HealthGuizhou Medical University Guiyang 550025 P. R. China
4. Maternal and Child Health Hospital of Baoan Shenzhen 518100 P. R. China