The endometrium is the inner lining of the uterus. Its primary function involves preparing for a potential pregnancy each month. This uterine lining thickens in response to hormonal signals, creating a hospitable environment for a fertilized egg to implant and grow. The thickness of the endometrium serves as an important indicator of uterine health and function.
Understanding Endometrial Thickness
This measurement is typically obtained through a transvaginal ultrasound, an imaging technique that uses sound waves to create detailed images of the uterus. Clinicians use this measurement to assess the health and condition of the endometrium, which can vary significantly depending on a person’s hormonal state and life stage.
The ultrasound measurement captures the thickest echogenic area of the lining. This imaging helps identify structural changes or abnormalities within the uterine cavity. The appearance of the endometrium on ultrasound also changes, from a thin, bright stripe during menstruation to a thicker, more uniform appearance in later phases of the menstrual cycle.
Normal Thickness Across Life Stages
The normal thickness of the endometrium is not a single, fixed number; instead, it fluctuates considerably based on a person’s age and hormonal status.
In pre-menopausal women, endometrial thickness undergoes cyclical changes throughout the menstrual cycle. During menstruation, when the lining is shed, its thickness is at its lowest, typically ranging from 2 to 4 millimeters (mm).
Immediately following menstruation, in the early proliferative phase (around days 5 to 14), estrogen causes the endometrium to begin rebuilding, reaching about 5 to 7 mm. As the cycle progresses into the late proliferative or pre-ovulatory phase, the lining continues to thicken, potentially reaching up to 11 mm. Following ovulation, during the secretory phase (approximately days 15 to 28), the endometrium becomes even thicker and more receptive, often measuring between 7 and 16 mm, and sometimes up to 18 mm.
For post-menopausal women not undergoing hormone replacement therapy (HRT), the endometrium typically becomes much thinner due to reduced hormone production. A normal endometrial thickness in this group is generally 3 to 5 mm or less.
However, for post-menopausal women who are on hormone replacement therapy, the endometrium can be thicker, as HRT introduces hormones that mimic the body’s natural processes. In these cases, an endometrial thickness of up to 8 to 11 mm may be considered acceptable, though 5 mm is often still a threshold for further evaluation. The specific type and regimen of HRT can influence this measurement.
When Thickness Deviates from Normal
When endometrial thickness falls outside of these expected ranges, it can indicate various conditions, some of which may require medical attention.
An endometrium that is too thick, a condition known as endometrial hyperplasia, often results from an imbalance of hormones, particularly an excess of estrogen without sufficient progesterone. Estrogen stimulates the growth of endometrial cells, while progesterone helps to regulate this growth and trigger shedding. Without enough progesterone, the lining continues to thicken abnormally.
This can lead to symptoms such as unusually heavy or prolonged menstrual bleeding, bleeding between periods, or post-menopausal bleeding. While not always cancerous, some forms of endometrial hyperplasia, particularly atypical hyperplasia, can increase the risk of endometrial cancer. Other causes of a thickened endometrium can include endometrial polyps or fibroids.
Conversely, an endometrium that is too thin can also present concerns, particularly for fertility. A thin endometrium is generally defined as a lining less than 7 mm. This condition can be caused by hormonal imbalances, such as low estrogen levels, or by uterine scarring from previous procedures or infections, a condition known as Asherman’s syndrome.
Poor blood flow to the uterus, chronic inflammation, or certain medical conditions like thyroid disorders and diabetes can also contribute to a thin lining. A thin endometrium may make it difficult for a fertilized egg to implant, potentially leading to infertility or recurrent miscarriages.
What Happens Next
If an abnormal endometrial thickness is detected, healthcare providers will typically recommend further evaluation to determine the specific cause.
One common diagnostic step is saline infusion sonohysterography (SIS), also known as a sonohysterogram. This procedure involves introducing a sterile saline solution into the uterus while performing an ultrasound, which helps to expand the uterine cavity and provide clearer images of the endometrial lining. This allows for better visualization of any polyps, fibroids, or other structural abnormalities that might be causing the thickening.
Another procedure that may be performed is a hysteroscopy. During a hysteroscopy, a thin, lighted tube with a camera is inserted through the vagina and cervix into the uterus, allowing the healthcare provider to directly visualize the uterine cavity. This direct view can help identify and, in some cases, remove polyps, fibroids, or scar tissue. Often, a hysteroscopy is combined with an endometrial biopsy, where a small tissue sample is taken from the lining for microscopic examination.
An endometrial biopsy helps determine if abnormal cells, hyperplasia, or cancerous cells are present. This can be done in an office setting or during a hysteroscopy. In some cases, a dilation and curettage (D&C) might be performed, especially if a larger tissue sample is needed or if a previous biopsy was inconclusive. A D&C involves dilating the cervix and gently scraping or suctioning tissue from the uterine lining. The management approach, which could include monitoring, medication, or surgical intervention, will depend on the findings from these diagnostic tests.