北京市卫生系统高层次卫生技术人才培养计划项目2009-3-52;首都医科大学附属北京妇产医院,北京妇幼保健院学科带头人项目2013-1。@@@@This study was supported by Beijing Municipality Health Technology High-level Talent2009-3-52;Project of Discipline Leader, Beijing Obstetrics and Gynecology Hospital, Capital Medical University, Beijing Maternal and Child Health Care Hospital2013-1