The lining of the uterus, the endometrium, thickens monthly during reproductive years in preparation for potential pregnancy, driven by estrogen and progesterone. If pregnancy does not occur, the lining sheds during menstruation. After menopause, the ovaries cease hormone production, causing a dramatic reduction in endometrial thickness as it enters a state of atrophy. Monitoring postmenopausal uterine health is done by measuring endometrial thickness using a transvaginal ultrasound. This non-invasive measurement serves as an initial screening tool to determine if further diagnostic steps are necessary.
Defining Normal Endometrial Thickness
The interpretation of transvaginal ultrasound measurements depends heavily on whether a woman is experiencing symptoms. For postmenopausal women presenting with vaginal bleeding, the clinical threshold for a reassuringly thin endometrium is typically 4 millimeters or less. A measurement at or below 4 mm has a high negative predictive value, making the presence of endometrial cancer extremely unlikely. This thin range often allows clinicians to confidently rule out malignancy without needing further invasive procedures.
For asymptomatic postmenopausal women, the interpretation is more nuanced. A measurement of 5 millimeters or less is often considered within a normal or low-risk range for these women. The goal of screening is to identify a thickness threshold sensitive enough to detect possible cancer without prompting excessive, unnecessary invasive procedures.
Clinical guidelines suggest that an asymptomatic postmenopausal woman usually does not require an immediate biopsy unless the thickness exceeds 10 to 11 millimeters. This higher threshold reflects that many benign conditions can cause slight thickening, and the risk of malignancy remains low without bleeding. The risk of underlying disease is determined by combining the measurement with the presence or absence of postmenopausal bleeding.
Potential Causes of Increased Thickness
An endometrial thickness measurement exceeding the normal threshold does not automatically indicate serious disease, as several conditions can cause the lining to thicken. A common cause is endometrial polyps, which are benign, localized growths projecting into the uterine cavity. Polyps are frequently found in postmenopausal women and often cause asymptomatic thickening detected incidentally during an ultrasound.
Another cause of increased thickness is endometrial hyperplasia, an overgrowth of the tissue. This condition is usually driven by unopposed estrogen, which continuously stimulates the lining without the counteracting effect of progesterone. Endometrial hyperplasia is considered a precancerous condition, with risk varying based on the presence of atypical cells.
Hormone Replacement Therapy (HRT) also influences measurements, as some regimens intentionally stimulate the lining with estrogen. Women on continuous combined HRT (estrogen and progesterone) typically maintain a thin endometrium. However, those on unopposed estrogen or certain sequential regimens may have an expected thickness of up to 8 to 11 millimeters, requiring different interpretation. The most concerning cause of a thickened endometrium is endometrial carcinoma, or cancer.
Diagnostic Steps Following Abnormal Results
When a transvaginal ultrasound reveals a measurement above the established threshold, the next step is to obtain a tissue sample for microscopic examination. The most common initial procedure is an endometrial biopsy, often performed using a thin, flexible tube called a Pipelle. This office-based procedure samples cells from the lining, which are analyzed to diagnose or rule out conditions like hyperplasia or cancer.
If the ultrasound suggests a focal abnormality, such as a polyp or fibroid, Saline Infusion Sonography (SIS), or sonohysterography, may be performed first. SIS involves injecting sterile saline solution into the uterine cavity during the ultrasound. This distends the uterus, allowing clearer visualization of the endometrial surface and helping distinguish global thickening from a localized mass.
If the initial biopsy is inconclusive, or if SIS reveals a suspicious focal lesion, a more comprehensive procedure may be necessary. This often involves hysteroscopy, where a thin telescope with a camera is inserted through the cervix to directly visualize the entire uterine cavity. Hysteroscopy can be combined with Dilation and Curettage (D&C), where the cervix is widened and a larger tissue sample is removed for analysis. Identifying underlying pathology is crucial, as early detection of endometrial cancer leads to high prognosis and cure rates.