Endometrial Thickening: Causes, Symptoms & Risks Explained

What is Endometrial Thickening?

Endometrial thickening occurs when the lining of the uterus is thicker than expected for a specific stage of the menstrual cycle. Normally, the lining grows and sheds each month under the influence of estrogen and progesterone.

It becomes a concern when the lining grows excessively, remains thick for an extended period or is detected after menopause. Persistent thickening can indicate endometrial hyperplasia, a condition in which the uterine lining grows abnormally and may require further evaluation to rule out serious problems.

What Causes Endometrial Thickening?

Endometrial thickening is most often caused by hormonal imbalance, especially excess estrogen without enough progesterone.

Common causes include:

• Hormonal imbalance, particularly unopposed estrogen
• Anovulatory cycles (when ovulation does not occur)
• Polycystic ovary syndrome (PCOS)
• Perimenopause or menopause-related hormonal changes
• Estrogen therapy without progesterone
• Obesity, as fat tissue produces extra estrogen
• Endometrial hyperplasia (abnormal thickening of the lining)
• Uterine polyps or fibroids

When is a Thickened Endometrium Considered Abnormal?

Endometrial thickening is considered abnormal when it does not correspond to a woman’s age, menstrual cycle phase or hormonal status.

Common concerning situations include:

• Persistent thickening despite regular periods
• Thickened lining after menopause
• Thickening accompanied by abnormal or unexpected bleeding

In postmenopausal women with bleeding, an endometrial thickness greater than 4 mm on transvaginal ultrasound usually requires further evaluation, such as endometrial sampling, as it is associated with a higher risk of pathology. Thickness of 4 mm or less in this group is linked to a very low risk of endometrial cancer.

What Are the Symptoms of Endometrial Thickening?

Symptoms of endometrial thickening can vary. Some women notice changes in their menstrual cycle, while others have no symptoms and discover it only during an ultrasound. The severity often depends on the underlying cause, age and hormonal status.

Common symptoms include:

• Heavy or prolonged menstrual bleeding
• Bleeding or spotting between periods
• Irregular cycles, including missed periods followed by heavy bleeding
• Postmenopausal bleeding, which always requires evaluation
• Mild pelvic discomfort or a feeling of pressure

These symptoms are often linked to hormonal imbalance, particularly excess estrogen without sufficient progesterone. This pattern is common in conditions such as irregular ovulation, polycystic ovary syndrome (PCOS), obesity, perimenopause and postmenopause and explains why the endometrium may thicken abnormally.

Can Endometrial Thickening Affect Fertility?

Yes. Abnormal endometrial thickening can interfere with implantation and reduce fertility. A lining that is too thick or hormonally unstable may:

• Lower the chances of embryo implantation if the endometrium is not receptive at the right time.
• Reflect irregular or absent ovulation, directly affecting fertility.
• Indicate hormonal imbalances, such as estrogen dominance or progesterone deficiency.
• Disrupt the timing between ovulation and endometrial readiness, making embryo attachment difficult.
• Be linked to conditions like endometrial hyperplasia, which may need treatment before conception.
• Affect fertility treatments, as an excessively thick or poorly prepared lining can reduce IVF or other assisted reproduction success.

How is Endometrial Thickening Diagnosed?

Diagnosis typically starts with imaging and may include tissue tests to determine the underlying cause. Common methods include:

• Transvaginal ultrasound: First-line test to measure endometrial thickness.
• Saline infusion sonography (SIS): Provides a clearer view of the uterine cavity.
• Pelvic examination: Assesses uterine size, shape and tenderness.
• Doppler ultrasound: Evaluates blood flow in the endometrium.
• Endometrial biopsy: Recommended if abnormalities are suspected, to rule out hyperplasia or cancer.
• Hysteroscopy: Allows direct visualisation and targeted sampling of the uterine lining.
• Dilation and curettage (D&C): Used if biopsy results are inconclusive.
• MRI scan: Detailed imaging in complex or high-risk cases.
• Hormonal blood tests: Identify estrogen or other hormonal imbalances linked to thickening.

What Thickness of Endometrium is Considered Concerning?

Concerning thickness depends on the reproductive stage:

What Are the Risks of Untreated Endometrial Thickening?

If a thickened endometrium is left untreated, it may continue to change over time. Risks depend on the underlying cause and duration of the condition:

• The lining may keep thickening, leading to endometrial hyperplasia, especially with prolonged high estrogen levels.
• Long-standing changes can slightly increase the risk of endometrial cancer.
• Persistent bleeding issues may occur, including heavier periods, spotting between cycles or postmenopausal bleeding.
• Fertility may be affected, as an unstable or excessively thick lining can make implantation difficult.
• Ongoing hormonal imbalance can drive further thickening.
• Delayed evaluation may allow related conditions, such as ovulatory or metabolic disorders, to remain undiagnosed.

How is Endometrial Thickening Treated?

Treatment depends on the cause, symptoms and reproductive goals. Common approaches include:

• Progesterone therapy: to balance hormones.
• Hormonal contraceptives: to regulate cycles and endometrial growth.
• Treatment of underlying conditions: such as PCOS.
• Surgical removal: of polyps or abnormal tissue.
• Regular monitoring: if no immediate risk is detected.

Can Lifestyle or Hormonal Changes Help?

Yes, lifestyle and hormonal adjustments can support treatment, though they do not replace medical management. Their effectiveness is clearer once the underlying cause of hormonal imbalance is identified:

• Body weight: Excess fat tissue can raise estrogen levels, affecting the uterine lining.
• Blood sugar and insulin resistance: Can disrupt normal hormone signals and cycle regulation.
• Thyroid and metabolic disorders: Often overlooked but common contributors to hormonal imbalance.
• Hormonal medications: Dosage and prolonged use should be periodically reviewed as they can influence endometrial growth.
• Diet and eating patterns: Irregular meals or poor nutrition can affect hormone metabolism.
• Physical activity: Lack of exercise may worsen insulin resistance and hormonal instability.
• Stress: Chronic stress can subtly disrupt reproductive hormones and menstrual cycles.
• Irregular ovulation: Prolonged estrogen exposure during missed or absent ovulation can worsen endometrial thickening.

Conclusion

Seeing endometrial thickening on a report can be confusing, but it does not always indicate a serious problem. For many women, especially those with regular menstruation, it may reflect normal hormonal changes.

The key is understanding why the thickening has occurred. Once the cause is identified, the next steps become clear: some cases require treatment, while others only need monitoring.

If you experience unusual bleeding, irregular periods, fertility concerns or an unexpected scan result, it is important to get a medical evaluation. Proper assessment provides clarity, reassurance and guidance, allowing you to make informed decisions calmly without unnecessary worry.