title: The absence of the vomer in the first and early second trimester of pregnancy - a new marker of trisomy 21 and trisomy 13.
abstract: OBJECTIVE
  The aim of this study was to measure the two frontomaxillo-facial (FMF) angles: the FMF-vomer (FMF-v) and the FMF-palate (FMF-p), and to visualize the vomer in the 1(st) and early 2(nd) trimester, in order to ascertain whether they can be used as markers for trisomy 21 and trisomy 13.
  
  
  METHODS
  A 2D ultrasound scan was performed in the 340 normal and 12 abnormal pregnancies, using the linear, convex and endovaginal probes.
  
  
  RESULTS
  We visualized the FMF angles within 1 to 5 minutes in 253 (72 %) of cases by using the linear probe. FMF-v angle was significantly smaller that the FMF-p angle (79.8° vs. 89.7°, 71.5° vs. 84.5° for the two trimesters, respectively), and that the value of both angles decreased in the second trimester. There was not one single case of trisomy in which vomer could be identified in the 1 (st) and early 2 (nd) trimester. The FMF-p angle failed to present difference between normal cases and the ones with trisomy (89.5°). There was not one single case of trisomy (21 or 13) in which vomer or FMF-v could be identified in the first or early second trimester. The diagnostic accuracy of vomer as a marker for trisomy was 0.985.
  
  
  CONCLUSIONS
  If the vomer cannot be visualized in the 1 (st) and early 2 (nd) trimester, it is important to check the karyotype, and it is not necessary to measure the FMF-p angle. The high resolution probe (L 12 - 5 Mhz) enables easier assessment of the vomer.
authors.affiliation: Department of Radiology, Ultramedica Clinic.
authors.forename: T
authors.initials: T
authors.lastname: Mihailovic
authors.forename: B V
authors.initials: BV
authors.lastname: Stimec
authors.forename: M
authors.initials: M
authors.lastname: Terzic
authors.forename: A
authors.initials: A
authors.lastname: Dmitrovic
authors.forename: J
authors.initials: J
authors.lastname: Micic
mesh_terms: D000649:Amniocentesis; D015193:Chorionic Villi Sampling; D025063:Chromosome Disorders / Q000000981:diagnostic imaging* / Q000196:embryology; D002882:Chromosomes, Human, Pair 13 / Q000000981:diagnostic imaging; D004314:Down Syndrome / Q000000981:diagnostic imaging* / Q000196:embryology; D019160:Endosonography / Q000379:methods*; D005260:Female; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D021621:Imaging, Three-Dimensional / Q000379:methods*; D009295:Nasal Bone / Q000002:abnormalities / Q000000981:diagnostic imaging; D048208:Nuchal Translucency Measurement / Q000379:methods; D011237:Predictive Value of Tests; D011247:Pregnancy; D011261:Pregnancy Trimester, First; D011262:Pregnancy Trimester, Second; D012680:Sensitivity and Specificity; D014262:Tricuspid Valve Insufficiency / Q000000981:diagnostic imaging / Q000196:embryology; D014314:Trisomy; D000073839:Trisomy 13 Syndrome; D016216:Ultrasonography, Prenatal / Q000379:methods*; D055172:Vomer / Q000002:abnormalities* / Q000000981:diagnostic imaging / Q000196:embryology