Thickened womb lining: what it means and when it needs investigating

The womb lining, called the endometrium, is the tissue that thickens each month in preparation for a pregnancy and is shed as a period. On an ultrasound scan its thickness is measured in millimetres. A thickened lining simply means that the measurement is higher than expected for your stage of life. It is a description, not a diagnosis, and the significance depends heavily on whether you are before or after the menopause and on whether you have symptoms.

Patient.info explains that the mean endometrial thickness in postmenopausal women is much thinner than in premenopausal women, and that thickening may indicate pathology. In general, the thicker the endometrium, the higher the likelihood that something important, such as endometrial cancer, is present. That is why a thick lining is followed up, even though most women with these findings turn out to have a benign cause.

For women who have been through the menopause and have bleeding, the interpretation is relatively specific. Patient.info says the British Gynaecological Cancer Society's 2021 guidelines recommend a cut-off endometrial thickness of 4 mm: women with postmenopausal bleeding and an endometrial thickness of less than 4 mm, without irregularities in the endometrium, can be reassured without further investigation unless bleeding recurs. It notes some uncertainty about the optimal cut-off, with some advocating 5 mm to improve specificity. Its endometrial hyperplasia reference says a cut-off of 3 to 4 mm is usually advised, and that where the endometrium measures more than this, further investigation is required.

Before the menopause the lining changes through the cycle, so a single measurement is less helpful. Patient.info says no standardised cut-off has been established in premenopausal women, thickness is less helpful because of cyclical change and overlap between normal proliferative endometrium and hyperplasia, and that an endometrial thickness below 7 mm is unlikely to represent hyperplasia. A scan report that mentions a thick lining in the second half of a cycle may therefore be entirely normal, and timing of the scan matters.

Patient.info lists causes of postmenopausal bleeding, which is often how a thick lining comes to light: vaginal atrophy (the most common cause), use of HRT, endometrial hyperplasia, endometrial cancer, endometrial or cervical polyps and, more rarely, cancers of the cervix, ovary, vagina or vulva. In the lining itself, thickening may reflect hyperplasia, polyps, hormonal treatment, or cancer.

Endometrial hyperplasia is caused by oestrogen that is not balanced by progesterone. Patient.info lists obesity, oestrogen use without cyclical progesterone, some oestrogen-secreting ovarian tumours, tamoxifen, polycystic ovary syndrome, never having had children, hereditary non-polyposis colorectal cancer and diabetes as risk factors, and says use of the combined oral contraceptive decreases risk. It also says the risk of progression to cancer is less than 5 percent over 20 years for hyperplasia without atypia, and as high as 28 percent over the same period for untreated atypical hyperplasia.

Patient.info says endometrial hyperplasia usually presents as abnormal vaginal bleeding: bleeding between periods, irregular bleeding, heavy periods or bleeding after the menopause, and there may be a vaginal discharge. Some thickening is found by chance when a scan is done for another reason, with no symptoms.

The NHS lists bleeding or spotting from the vagina after the menopause, heavy periods that are unusual for you, bleeding between periods and a change in vaginal discharge as the main symptoms of womb cancer, and says to see a GP if you have any of them. It stresses that these symptoms are common and have many causes, that having them does not definitely mean cancer, and that you should not wait to get them checked. Patient.info says NICE recommends urgent referral to a gynaecological cancer service for women over 55 with postmenopausal bleeding.

• Any bleeding after the menopause, including spotting, needs a GP appointment.

• Bleeding between periods or unusually heavy periods should be checked.

• Tell your doctor if you take tamoxifen or HRT, as this changes how findings are interpreted.

The NHS lists the main tests for suspected womb cancer as a transvaginal scan, blood tests, hysteroscopy and a biopsy of the womb lining, which may be done during hysteroscopy or separately. It says the tests should not be painful, but some are uncomfortable, and that results should arrive within a few weeks.

Patient.info describes the options in more detail. A transvaginal ultrasound is the first-line test to identify which women are at higher risk. An endometrial biopsy, now usually an outpatient procedure using a sampler such as a Pipelle, gives a histological diagnosis, though it can miss some pathology and an adequate sample is not always obtained. Hysteroscopy, in which a thin telescope is passed through the cervix, is the preferred technique for detecting polyps and other benign lesions, and may be done as an outpatient or occasionally under general anaesthetic. Referral to one-stop clinics, where several investigations are done at one visit, is described as ideal.

Treatment depends on the cause. If the biopsy shows no atypia, Patient.info describes reassurance, addressing risk factors such as obesity and hormonal medicines, and sometimes watchful waiting with follow-up biopsies. Progestogen treatment is the usual management, with the levonorgestrel intrauterine system as first-line because it is more effective and has fewer adverse effects, and continuous oral progestogens as second line, with follow-up biopsies until two consecutive samples are negative. Hysterectomy is not normally indicated but may be offered if there is no regression after a year of treatment, a change to atypical hyperplasia, relapse, or personal preference.

For atypical hyperplasia, Patient.info says total hysterectomy is advisable for all women because of the risk of malignant progression, with removal of the ovaries in postmenopausal women, while progestogen with regular biopsy may be used where fertility is to be preserved. Hysteroscopy is also the preferred technique to detect polyps and other benign lesions. If cancer is found, a specialist team will explain staging tests and treatment.

On the NHS, bleeding after the menopause is referred urgently to a gynaecology service, often a one-stop clinic. Premenopausal findings are assessed in the context of symptoms and may be repeated. Private gynaecology scans and hysteroscopy are available in the UK. Because an incidental thick lining on a private scan can cause worry, take the report to your GP or gynaecologist for interpretation.