Ultrasound Anatomy of the Uterus at Term

The evaluation of uterine anatomy at term is challenging. The grown fetus usually obstructs the view of the posterior elements of the uterus. The evaluation of adnexa and ovaries is also often not possible as the structures are high up in the abdominal cavity and out of the scanning depth. Luckily, pathologies requiring the assessment of adnexa are relatively rare at term pregnancies. The focus of anatomic ultrasound at term is the evaluation of the lower uterine segment, the placenta, the cervix, and the bladder. These structures have clinical relevance due to conditions such as placenta previa, placenta accrete spectrum (PAS), and risk assessment for a trial of labor after cesarean. The uterus undergoes significant changes throughout pregnancy and at term; the fully developed lower uterine segment (LUS) is present by 37 weeks’ gestation. We will discuss the formation of LUS and its surgical relevance later on in this chapter.