The endometrium is the inner lining of the uterus. Menopause is defined as twelve consecutive months without a period, after which the body’s hormonal environment fundamentally changes. This lack of hormonal stimulation causes the endometrium to atrophy, or thin out. Measuring this lining after menopause is a standard procedure used to assess uterine health and screen for precancerous changes or endometrial cancer. Deviations from this expected thinning prompt further medical investigation.
The Expected Postmenopausal Measurement
The normal thickness of the endometrium in a woman who has completed menopause and is not using hormone therapy is generally quite thin, which is a sign of good health. Without the cyclic stimulation of estrogen and progesterone, the tissue becomes quiescent. It should measure 4 millimeters (mm) or less.
This numerical threshold is not a one-size-fits-all rule and is interpreted differently based on the patient’s symptoms. For women who experience postmenopausal bleeding, a measurement of 4 mm or less is highly reassuring, as it rules out endometrial cancer with high certainty. When the measurement is below this threshold, the risk of malignancy is less than one percent, meaning no further invasive testing is usually necessary.
For postmenopausal women who are asymptomatic, the interpretation of the measurement can be more flexible. While 4 mm or less is ideal, some clinicians find measurements up to 8 mm or even 11 mm acceptable in the absence of symptoms. This difference reflects that in asymptomatic women, a slightly thicker lining is more likely to be a benign finding, such as a small polyp, rather than cancer. The diagnostic focus is much sharper for women who present with bleeding.
Symptoms That Prompt Evaluation
The most significant symptom prompting evaluation is Postmenopausal Bleeding (PMB). PMB is defined as any instance of vaginal bleeding, spotting, or staining that occurs after a woman has reached menopause. This symptom is the primary reason a physician orders a measurement of the endometrial lining.
Because bleeding is the most common presenting symptom of endometrial cancer, it must be thoroughly investigated to rule out malignancy. Approximately 90% of women diagnosed with endometrial cancer first experience PMB. Any report of bleeding, even a single episode of light spotting, should be immediately reported to a healthcare provider.
The investigation begins with a transvaginal ultrasound to measure the endometrial thickness. This measurement helps the physician quickly stratify the patient’s risk. If the thickness is within the normal, thin range, the cause of the bleeding is likely benign, such as atrophy or an issue with the lower genital tract. If the thickness is above the established threshold, additional procedures are needed to determine the precise cause.
Conditions That Cause Thickening
When the endometrial thickness exceeds the normal range, it indicates the lining is being stimulated to grow, usually by estrogen. This unopposed estrogen exposure can be generated within the body (e.g., significant obesity) or introduced externally through certain medications. Understanding the cause of the thickening is necessary to determine the appropriate course of action.
One common cause is Hormone Replacement Therapy (HRT), specifically regimens that include estrogen. Estrogen alleviates menopausal symptoms, but it intentionally causes the endometrium to proliferate, resulting in a thicker lining. For women on combination HRT, which includes progesterone, a thickness of up to 5 mm is often the acceptable limit. For those on sequential HRT, which involves cyclical bleeding, the thickness will vary throughout the cycle.
Beyond HRT, endometrial hyperplasia is a condition where the lining becomes overly thick and may contain abnormal cells. This condition is categorized as either simple hyperplasia (generally benign) or atypical hyperplasia (a precancerous condition with a higher potential to progress to cancer). Endometrial polyps, which are localized, usually benign overgrowths, are another frequent finding that can increase the total measured thickness.
The most serious cause of a thickened endometrium is Endometrial Carcinoma, a cancer of the uterine lining. While most cases of thickening are benign, the risk of cancer increases incrementally as the measurement rises above the 4 mm or 5 mm threshold.
Diagnostic Procedures Following Abnormal Results
The first step in evaluating a concerning endometrial measurement is typically a Transvaginal Ultrasound (TVUS). This procedure uses sound waves transmitted through a probe inserted into the vagina to create an image of the uterus, allowing for the precise, non-invasive measurement of the double-layer lining. If the TVUS reveals a thickness above the concerning threshold, further diagnostic steps are required to obtain a tissue sample.
The definitive method for diagnosing the cause of the thickening is an Endometrial Biopsy. This involves taking a small sample of the uterine lining for microscopic examination. The procedure is often performed in an outpatient setting using a thin suction catheter, such as a Pipelle, to collect cells from the entire cavity. The biopsy determines if the thickening is due to benign tissue, hyperplasia, or carcinoma.
If the biopsy sample is insufficient or if a focal lesion, like a polyp, is suspected, Hysteroscopy may be utilized. This involves inserting a thin, lighted tube with a camera through the cervix into the uterus to visually inspect the uterine cavity. During this inspection, targeted biopsies can be taken, or focal lesions can be removed.
Sometimes, a Dilation and Curettage (D&C) procedure is performed, often with a hysteroscopy, to fully scrape the lining and obtain a larger tissue sample for diagnosis.