Figure 2.

Illustration of different types of challenges. A, The white arrows show the substantial interference of noise and shadowing effect. B, In the upper graph, the blue box represents the real brain midline, and the orange box is the confusing anatomical structure with a similar shape. In the lower figure, the orange box represents the actual gallbladder, and the blue box represents the real umbilical vein. These 2 structures have a very similar shape. C, FS images with different fetal positions, which will cause significant variations for the appearance of the images. FS = fetal sonographic.