国家自然科学基金81370277,81370279;江苏省科技厅临床医学专项BL2013003;江苏省卫生厅妇幼保健科研课题重点资助项目 F201309 National Natural Science Foundation of China81370277, 81370279;Jiangsu Provincial Special Pro-gram of Medical ScienceBL2013003;Jiangsu Provincial Key Support for Maternal and Child Health CareF201309