Endometrium on ultrasound: how I read the thickness and the report

Endometrial thickness by cycle day

The endometrium is the lining of the inside of the uterus. Every cycle it follows the same path: it grows under estrogen, after ovulation it becomes denser under progesterone and prepares to receive an embryo, and if there is no pregnancy it is shed. That is why it looks different on ultrasound from day to day, and why it has to be compared not with “normal in general” but with normal for that day.

These ranges are guides, not borders beyond which disease begins. A difference of 2–3 mm between two healthy women on the same cycle day is ordinary.

How the endometrium is measured

I measure with a transvaginal probe: it sits a couple of centimeters from the uterus, so the layers are clearly visible. Thickness can be estimated through the abdomen too, but much more roughly.

• I bring the uterus into a longitudinal (sagittal) view, so that the whole cavity is visible from the fundus to the cervix.
• I measure at the thickest point, perpendicular to the cavity, from outer border to outer border. The figure includes both layers at once, front and back, which is why reports sometimes say “double-layer thickness”.
• The dark rim around the endometrium is already the inner layer of the uterine muscle; it is not included.
• If there is fluid in the cavity, each layer is measured separately and the two are added; the fluid itself does not count.

A difference of 1–2 mm between two scans or two examiners is ordinary measurement error, not “growth” or “thinning”. Sometimes the endometrium cannot be shown in full: a fibroid, adenomyosis or the position of the uterus gets in the way. The right thing then is to write “not clearly visualized” rather than put down a guess.

Words in the report and what they mean

• Endometrial stripe, endometrial echo. The same measurement under another name: the thickness of the endometrium in millimeters. Reports from Ukraine and Russia call it “M-echo”.
• Three-layer (trilaminar). The pattern of the first half of the cycle: the endometrium is growing under estrogen. Before ovulation it is a good sign.
• Hyperechoic, secretory type. The bright, uniform endometrium of the second half of the cycle. It means ovulation most likely happened and progesterone is at work.
• Heterogeneous. The vaguest word of all. Just before a period and in its first days the endometrium is heterogeneous in everyone. If that is written on day 5–10, I look for a cause: a polyp, an area of hyperplasia, tissue left after a miscarriage or birth, occasionally inflammation.
• Does not match the cycle day. Most often the cycle itself has shifted: ovulation came later than usual or did not come at all. Hormonal medication gives the same picture. And a thick “secretory” endometrium with a late period is first of all a reason to take a pregnancy test.
• Suspected endometrial polyp. A bright, well-outlined structure in the cavity, often with a single feeding vessel. It shows best right after a period, while the lining is thin. If I am unsure, I ask the patient back for a repeat scan on day 5–10 of the next cycle.
• Suspected hyperplasia. An endometrium thicker than it should be for the day, often heterogeneous. Hyperplasia is a diagnosis made under the microscope: ultrasound can only raise the suspicion, and examining the tissue confirms or dismisses it.
• Thin endometrium. Usually written when it measures less than 7 mm before ovulation. On the contraceptive pill or with a hormonal coil a thin endometrium is the expected effect of the medication, not a finding.

How to read the other lines — uterus, ovaries, free fluid — is covered in my article on the pelvic ultrasound report.

The endometrium when you are trying to conceive

Two things matter here: thickness before ovulation, and pattern. The usual guide is 7 mm or more with a three-layer structure. It comes from reproductive medicine: in IVF programs pregnancy is less frequent when the endometrium is thinner. But that is statistics, not a threshold below which pregnancy is impossible: pregnancies happen at 6 mm too, and a 10 mm endometrium guarantees nothing on its own.

If the endometrium is thin cycle after cycle, I look for the reason first: past curettage or surgery on the uterus, long-term hormonal contraception, ovulation induction with clomiphene, low estrogen, past inflammation. Reliable ways of “thickening” the endometrium with proven benefit are few — professional guidelines say so as well — so I do not prescribe everything at once “for thickness”.

It makes sense to assess the endometrium on the same days the follicle is maturing, during folliculometry. One visit shows both the size of the dominant follicle and whether the lining is ready. The whole cycle is described in my article on ovulation on ultrasound.

After menopause the logic is different

Once periods have been absent for a year or more, the endometrium stops changing with the cycle and stays thin. The question is no longer “which day” but “is there any bleeding or spotting”.

• There is bleeding or spotting. An endometrium of 4 mm or less makes endometrial cancer very unlikely — that is the position of the American College of Obstetricians and Gynecologists (ACOG, 2018); some European protocols use 4–5 mm as the limit. Thicker than that calls for a tissue diagnosis: hysteroscopy or endometrial biopsy. And most importantly: if the bleeding comes back, evaluation is needed whatever the thickness.
• No bleeding, thickening found by chance. The 4 mm threshold does not carry over. What counts is the figure, the structure and the risk factors: obesity, diabetes, estrogen taken without a progestogen. Around 11 mm is often quoted as a guide for further tests without bleeding, but the decision is always individual.
• Tamoxifen. On tamoxifen the endometrium often looks thick and “cystic” on ultrasound with no disease at all. So a scan “just in case” adds little for women taking it, while any bleeding is a reason to be evaluated.
• Menopausal hormone therapy. On a cyclical regimen the endometrium follows the medication and is best measured right after the withdrawal bleed ends. On a continuous regimen spotting in the first months is common; if it lasts longer than six months or starts later, it needs evaluation.

One more thing: a thin, even stripe is reassuring only when the endometrium is seen in full. If it could not be shown, the number cannot be trusted — and I say so plainly in the report.

When not to wait

• any bleeding or spotting after menopause, even once and even slight;
• bleeding between periods or after sex;
• periods have become clearly heavier: a pad or tampon lasting an hour or two, clots, weakness, low hemoglobin;
• the scan report says “polyp”, “hyperplasia?” or “lesion in the uterine cavity”;
• no pregnancy after a year of trying, or after six months if you are over 35.

What I do at the visit and what it costs

At the visit I examine the endometrium transvaginally, measure it by the rules described above, assess its structure and blood flow, and explain straight away what I see and what follows from it. A routine pelvic ultrasound is best done on day 5–10 of the cycle: the lining is thin, and a polyp or a fibroid in the cavity has nowhere to hide. If the question is ovulation and whether the endometrium is ready, we pick the days by folliculometry. After menopause, or with bleeding, there is no day to choose — come right away.

• pelvic ultrasound — 250 zł;
• consultation — 290 zł;
• consultation with ultrasound at one visit — 450 zł;
• folliculometry — 160 zł per visit.

I take endometrial biopsies in the office: it is a short procedure without general anaesthesia, and the sample goes for histology; I will tell you the price when you book. I do not perform hysteroscopy in the office — it is an operating-room procedure: I will explain why it is needed and where it is done, and give you a detailed ultrasound description. We can then go through the histology result together.

I see patients in Warsaw, in the Targówek district, at ul. Głębocka 9/U1. Consultations are in Polish, Ukrainian or Russian. No referral or insurance is needed. You can choose a time on the booking page.

Short answers

Sources

The primary sources this text rests on. Links open in a new tab.

1. ACOG Committee Opinion No. 734: The Role of Transvaginal Ultrasonography in Evaluating the Endometrium of Women With Postmenopausal Bleeding (2018)American College of Obstetricians and Gynecologists — the 4 mm threshold in postmenopausal bleeding and what to do when bleeding recurs
2. Leone FPG et al. Terms, definitions and measurements to describe the sonographic features of the endometrium and intrauterine lesions: a consensus opinion from the International Endometrial Tumor Analysis (IETA) group. Ultrasound Obstet Gynecol 2010;35:103–112the IETA group consensus — how the endometrium is measured and which terms describe it
3. NICE guideline NG88: Heavy menstrual bleeding: assessment and managementNICE, UK — assessment of heavy periods: when ultrasound, when hysteroscopy and biopsy
4. Liu KE, Hartman M, Hartman A. Management of thin endometrium in assisted reproduction: a clinical practice guideline from the Canadian Fertility and Andrology Society. Reprod Biomed Online 2019;39:49–62Canadian Fertility and Andrology Society — what is known about thin endometrium and why reliable ways to “thicken” it are few
5. Smith-Bindman R, Weiss E, Feldstein V. How thick is too thick? When endometrial thickness should prompt biopsy in postmenopausal women without vaginal bleeding. Ultrasound Obstet Gynecol 2004;24:558–565the origin of the roughly 11 mm guide for an incidental finding after menopause without bleeding

This text describes the general picture and does not replace a consultation. Timings and indications differ from woman to woman and are decided at the appointment, from your history and test results.