Endometrial Thickness — What Is Normal, and When It Is Not

A postmenopausal lining should be thin and stay thin, because the hormone cycle that thickens it each month has stopped. Published thresholds exist below which cancer is considered unlikely enough to avoid a biopsy, but the exact figure varies between guidelines and between units, and it only applies to a specific situation: a postmenopausal woman being investigated for bleeding. It does not transfer to a woman with no symptoms, or to a woman on hormone therapy. Rather than take a number from a website, ask the clinician who ordered your scan which threshold they use and how your result compares.

Not automatically, and this is a genuinely common scenario — a thickened lining found on a scan ordered for something else entirely. The published thresholds were derived in women who had bled, and applying them to women without symptoms leads to a large number of biopsies that find nothing. What usually happens instead is that the finding is weighed against your risk factors: age, body weight, diabetes, hormone use, and family history. Some women in that situation are offered sampling and many are not. It is a judgement, and it should be an explained one.

Yes, in several situations. If you are still having periods, a thick lining in the second half of your cycle is exactly what should be there. If you are on hormone replacement therapy, the lining stays more active and reads thicker, and that is expected rather than abnormal. If you are on certain hormonal breast cancer treatments, thickening occurs in most women who take them. And sometimes the measurement is an artefact — a fibroid pressing on the cavity or fluid inside it can both inflate the figure without the lining itself being abnormal.

No — and this is the single most useful thing on this page. A thin lining makes endometrial cancer unlikely, but persistent bleeding is a stronger signal than a reassuring measurement. A small focal cancer, or one inside a polyp, can sit in a lining that measures thin overall. Ongoing or recurrent bleeding after a normal scan is a recognised indication to investigate further, usually with tissue sampling or hysteroscopy so the cavity can be looked at directly. If you feel your continuing symptoms are being weighed against an old scan, say so plainly.

Not reliably. The measurement reflects how much tissue is present, which is affected by where a tumour sits, whether there is a polyp, whether blood or fluid is in the cavity, and how well the scan visualised things. It is not a measure of stage or grade. Staging comes from what is found at surgery together with imaging such as MRI, and grade comes from the pathologist examining the cells. Women sometimes arrive very frightened by a large number on a scan report; it is genuinely not the number that determines the outlook.