Sonographic images of monochorionic twins Sonographic images of monochorionic twins. A: Absence of visible intertwin septum in a 7-week pregnancy with closely located embryos. B: T sign in a 12-week twin gestation with the 2 layers of amnion justaposed. C: Three-dimensional scan showing the 2 layers of amnion. Source: SONOGRAPHY IN MULTIPLE GESTATION, Sonography in Obstetrics and Gynecology: Principles & Practice, 7e Citation: Fleischer AC, Toy EC, Lee W, Manning FA, Romero RJ. Sonography in Obstetrics and Gynecology: Principles & Practice, 7e; 2014 Available at: https://obgyn.mhmedical.com/DownloadImage.aspx?image=/data/books/1414/fle_ch13_f011.png&sec=76391808&BookID=1414&ChapterSecID=76391764&imagename= Accessed: November 15, 2017 Copyright © 2017 McGraw-Hill Education. All rights reserved