Avoiding ambiguity in the sonographic determination of the direction of umbilical cord twists

The helical twisting pattern of umbilical cord vessels is a well-recognized phenomenon, and the direction of twisting can be easily determined by gross pathologic inspection. With the cord held vertically, vessels along the anterior surface that spiral downward from high left to low right, angled like the left side of the letter V, indicate a left helix. Those angled like the right side of the V form a right helix. However, confusion can occur in determining the direction of spiraling on prenatal sonographic images depending on whether the image plane transects the cord along the surface toward or away from the observer. For correct identification of the direction of the cord twist, images must be obtained along the nearer surface.