Measurement of the pelvis sometimes requires testing from the anus, and the main purpose of the test is to determine whether the back half of the pelvis is normal. The anterior half of the pelvis can be examined through a vaginal examination, but if the tailbone is found to be more convex, or if there is a possibility of narrowing of the sciatic spine, a further anal examination should be done. The anal examination can detect the curvature of the tailbone and the distance between the sciatic spines to further examine the shape of the pelvis. In addition to measuring the pelvis, anal examination can also clarify the stiffness of the cervix and the degree of dilatation of the uterine opening, making anal examination an important test during pregnancy.