The cervix is the aperture or route through which the infant must pass before to vaginal birth. To anticipate preterm birth, ultrasound can identify early changes in the cervix, such as shortening of the cervical length. > span Using ultrasound to measure the thickness of the cervix has been proposed as a method for predicting who will go into labor prior to term. The hypothesis is that women with thinned out cervices will begin to show signs of labor earlier than those with thicker cervices. However, there is no evidence that this technique is effective for predicting premature birth. Ultrasound is also used to diagnose diseases of the uterus and ovaries, such as cancer. This image shows two large blood vessels in the uterus, known as the uterine arteries. These vessels are usually visible on ultrasound images of the pelvis. They can be identified by their dark appearance against the lighter colored myometrium (muscle wall) of the uterus. Uterine fibroids are common benign (noncancerous) tumors of the uterus. They may cause menorrhagia (heavy menstrual bleeding), infertility, and abdominal pain. Fibroids contain collagen and muscle fibers like those found in the uterus itself but are composed mainly of fatty tissue. They do not invade surrounding tissues nor do they metastasize (spread) via the blood stream or lymph system.