[1] Torloni MR,Vedmedovska N,Merialdi M,et al. Safety of ultrasonography in pregnancy:WHO systematic review of the literature and meta-analysis [J]. Ultrasound Obstet Gynecol,2009,33:599-608.[2] Fowlkes JB. American Institute of Ultrasound in Medicine consensus report on potential bioeffects of diagnostic ultrasound[J]. J Ultrasound Med,2008,27:503-515.[3] American Institute of Ultrasound in Medicine. AIUM practice guideline for the performance of obstetric ultrasound examinations[J]. J Ultrasound Med,2013,32:1083-1101.[4] Whitworth M,Bricker L,Neilson JP,et al. Ultrasound for fetal assessment in early pregnancy[J].Cochrane Database Syst Rev,2010,CD007058. doi:10.1002/14651858.CD007058.[5] Taipale P,Hiilesmaa V. Predicting delivery date by ultrasound and last menstrual period in early gestation[J]. Obstet Gynecol,2001,97:189-194.[6] Salomon LJ,Alfirevic Z,Bilardo CM,et al. ISUOG practice guidelines:performance of first-trimester fetal ultrasound scan[J]. Ultrasound Obstet Gynecol,2013,41:102-113.[7] Syngelaki A,Chelemen T,Dagklis T,et al. Challenges in the diagnosis of fetal non-chromosomal abnormalities at 11–13 weeks[J]. Prenat Diagn,2011,31:90-102.[8] National Collaborating Centre for Women’s and Children’s Health. Antenatal care:routine care for the healthy pregnant woman[M].London UK:RCOG Press,2008.[9] Rochon M,Eddleman K. Controversial ultrasound findings[J].Obstet Gynecol Clin North Am,2004,31:61-99.[10] Bromley B,Lieberman E,Shipp TD,et al. The genetic sonogram:a method of risk assessment for Down syndrome in the second trimester[J]. J Ultrasound Med,2002,21:1087-1096.[11] Bromley B,Lieberman E,Shipp TD,et al. Fetal nose bone length:a marker for Down syndrome in the second trimester[J]. J Ultrasound Med,2002,21:1387-1394.[12] Bahado-Singh RO,Oz UA,Mendilcioglu I,et al. The mid-trimester genetic sonogram[J]. Semin Perinatol,2005,29:209-214.[13] Yeo L,Vintzileos AM. The use of genetic sonography to reduce the need for amniocentesis in women at high-risk for Down syndrome[J]. Semin Perinatol,2003,27:152-159.[14] Warshak CR,Eskander R,Hull AD,et al. Accuracy of ultrasonography and magnetic resonance imaging in the diagnosis of placenta accreta[J]. Obstet Gynecol,2006,108:573-581.[15] McLean LA,Heilbrun ME,Eller AG,et al. Assessing the role of magnetic resonance imaging in the management of gravid patients at risk for placenta accreta[J]. Acad Radiol,2011,18:1175-1180.[16] Magann EF,Doherty DA,Ennen CS,et al. The ultrasound estimation of amniotic fluid volume in diamniotic twin pregnancies and prediction of peripartum outcomes[J]. Am J Obstet Gynecol,2007,196:570.e1-e6.[17] Hu LS,Caire J,Twickler DM. MR findings of complicated multifetal gestations [J]. Pediatr Radiol,2006,36:76-81.[18] Kline-Fath BM,Calvo-Garcia MA,O’Hara SM,et al. Twin-twin transfusion syndrome:cerebral ischemia is not the only fetal MR imaging finding[J]. Pediatr Radiol,2007,37:47-56.[19] Avni FE,Guibaud L,Robert Y,et al. MR imaging of fetal sacrococcygeal teratoma:diagnosis and assessment[J]. AJR Am J Roentgenol,2002,178:179-183.(2015-04-03收稿)