The absence of the vomer in the first and early second trimester of pregnancy - A new marker of trisomy 21 and trisomy 13

Abstract

Purpose: 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 1st and early 2nd trimester, in order to ascertain whether they can be used as markers for trisomy 21 and trisomy 13. Materials and 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 1st and early 2nd 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. Conclusion: If the vomer cannot be visualized in the 1st 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. © Georg Thieme Verlag KG Stuttgart · New York.