国家自然科学基金项目81172518;北京市科技新星交叉合作项目Z14111000180000;北京市卫生系统高层次卫生技术人才培养计划项目2014-2-016;首都医科大学附属北京妇产医院学科带头人项目2013-1。 This study was supported by National Natural Science Foundation of China81172518;Beijing Nova ProgramZ14111000180000;Beijing Municipality Health Technology High-level Talent2014-2-016;Project of Discipline Leader, Beijing Obstetrics and Gynecology Hospital, Capital Medical University2013-1