The endometrium is the lining of the uterus. The body prepares the endometrium to host an embryo during the menstrual cycle. Depending on what stage of the cycle a person is in, endometrial thickness varies from 1–18 millimeters (mm).

Two hormones, estrogen and progesterone, prompt the cycles of endometrial growth and shedding through menstruation if a pregnancy does not occur.

This article explains the typical range for endometrial thickness, causes of changes, and when to contact a doctor.

A note about sex and gender

Sex and gender exist on spectrums. This article will use the terms “male,” “female,” or both to refer to sex assigned at birth. Click here to learn more.

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The typical thickness of the endometrium changes throughout a person’s life, from childhood to puberty, through reproductive years, and after menopause.

Older research reports that in imaging tests of females who have not yet begun menstruating, the endometrium is present but smaller than it likely will be later in life.

According to a 2021 study, the endometrium is at its thinnest during menstruation, typically measuring between 1–4 mm in thickness.

The first half of the proliferative phase starts between days 5–14 of a person’s cycle, or the time between the end of one menstrual cycle, when bleeding stops, and before ovulation. During this phase, the endometrium begins to thicken and may measure between 10–16 mm.

About 14 days into a person’s cycle, hormones trigger the release of an egg. During this secretory phase, endometrial thickness is at its greatest and can reach 18 mm.


Endometrial thickness is important in pregnancy. If a person wishes to become pregnant, healthcare professionals link the best chance of a full-term pregnancy with an endometrium that is neither too thin nor too thick. This optimal thickness allows the embryo to implant correctly and receive the nutrition it needs. The endometrium gets thicker as the pregnancy progresses.

However, more recent research suggests a thin endometrium (less than 7 mm) has a detrimental effect on pregnancy outcomes. There may be increased risks of:

  • hypertensive disorders of pregnancy
  • infants who are small for their gestational age
  • decreased birth weight of newborns


The Radiological Society of North America states that in otherwise well people who have undergone menopause, the endometrium typically measures about 5 mm or less, according to older research.

However, there is a lack of consensus about the significance of endometrial thickness of more than 4 mm in people who have undergone menopause.

A study from 2022 suggests that females who have undergone menopause with an endometrial thickness of 9.5 mm or more are more likely to experience endometrial malignancy, including endometrial cancer.

Ultrasound is the most common way to measure the thickness of the endometrium. It is the method that healthcare professionals tend to use first, especially if an individual has reported abnormal vaginal bleeding.

When ultrasound is not suitable, often due to the position of a person’s uterus or other health conditions, a healthcare professional may recommend an MRI.

The thickness of the endometrium changes during a person’s menstrual cycle, but other factors can prompt changes as well.

One of the more common causes of changes in endometrial thickness is pregnancy. A person experiencing an ectopic pregnancy or who is less than 5 weeks pregnant may show signs of a thickening endometrium, according to older research.

Cancer of the endometrium or the ovaries is one of the most severe conditions that can lead to an increase in endometrial thickness.

According to the American Cancer Society, endometrial cancer is the most common cancer of the female reproductive system. It develops more often in African American people than white people and is rare in people under 45 years old. The average age at diagnosis is 60 years old.

Other factors contributing to a greater thickness of the endometrium include:

Endometrial hyperplasia is the medical term for a condition in which the endometrium becomes too thick. This often has links with excessive levels of estrogen or estrogen-like compounds and not enough progesterone. The condition itself is not cancer, but it can lead to the development of cancer.

It is also possible for the endometrium to be too thin. Older research defines a thin endometrium as 7 mm or less. Typically, experts associate low readings of endometrial thickness with age. However, they report that 5% of people under 40 years old and 25% of people over 40 years old had a thin endometrium.

Possible causes of a thin endometrium include inflammation, medical treatment, or the structure and nature of the endometrium itself.

The most common signs of excessive endometrial thickness include:

Treatments for excessive endometrial thickness include progestin, a female hormone that prevents ovulation, and hysterectomy.

Studies show that it is more difficult for a pregnancy to progress when readings for endometrial thickness are low. Treatments for a thin endometrium can include:

  • estrogen
  • human chorionic gonadotrophin, which is a hormone that the placenta produces after an embryo implants in the uterus wall
  • medications and supplements used to improve blood flow

However, research shows that these treatments are not consistently effective.

People should contact a doctor if they notice abnormal vaginal bleeding, which can include:

  • spotting between periods
  • unusually heavy flows
  • irregular, short blood flows
  • vaginal bleeding or spotting after menopause

People experiencing pelvic pain of unknown origin should contact a doctor for evaluation and to rule out endometrial cancer. Other symptoms to watch out for are bloating and a feeling of fullness without eating much.

Below are some commonly asked questions about endometrium thickness.

What is typical endometrium thickness?

What experts consider a typical endometrium thickness changes throughout a person’s life. During menstruation, depending on what stage in their cycle a person is in, endometrial thickness varies from 1–18 mm.

How thick is a cancerous endometrium?

Endometrium thickness alone may not be a definitive indicator of cancer.

Doctors typically diagnose cancerous changes in the endometrium, such as endometrial cancer, using imaging studies, biopsy, or other medical procedures.

One study suggests that females who have undergone menopause and who have an endometrial thickness of 9.5 mm or more are more likely to experience endometrial malignancy, including endometrial cancer.

However, experts need to conduct more research on this topic.

Having endometrial thickness measured may help people who are trying to become pregnant to understand the best way to optimize their chance of conception.

Changes in endometrial thickness are common throughout a person’s life. However, if someone notices abnormal bleeding, discharge, pelvic pain, or other changes in the way their body feels, they should consult a doctor.

Endometrial cancer is one of the most severe health problems that can occur if a person’s endometrium is too thick. However, endometrial cancer often has a high survival rate if diagnosed early.