1. Department of Obstetrics and Gynecology, Peking University International Hospital, Beijing 102206, P.R. China
2. Department of Orthodontics, School of Stomatology, Capital Medical University, Beijing 100050, P.R. China
3. Department of Translational Medicine Laboratory, First Medical Center of People's Liberation Army General Hospital, Beijing 100039, P.R. China
4. Department of Prenatal Diagnosis Center, Haidian Maternal and Child Health Care Hospital, Beijing 100080, P.R. China