The Normal Uterus

The uterus as a reproductive organ undergoes changes in response to ovarian hormones in preparation for implantation of the fertilized ovum and maintenance of pregnancy. Most changes are at the level of the endometrium and can be detected by pelvic sonography. Ultrasound is the modality of choice for pelvic organ imaging. Early proliferative endometrium appears as a thin echogenic line. Under the influence of increasing estradiol hormone levels (secreted by the growing ovarian follicles), the endometrial proliferation occurs. Sonographically, this is visualized as thickening of the lining into the trilaminar layer with an anterior and posterior hypoechoic layers bordering the myometrium separated by hyperechogenic central line. The post-ovulatory endometrium is under the influence of progesterone secreted by the corpus luteum, and the lining is characterized by loss of the trilaminar appearance and the development of a uniform echogenic stripe. The cervix also undergoes cyclical changes that are detectable on sonography.