Endometrium

What is the endometrium?

The endometrium is a mucous membrane that lines the inside of your uterus. It’s the tissue that sheds when you have your period. And it’s essential for maintaining a pregnancy.

The endometrium constantly changes and regenerates during your menstrual cycle. Researchers estimate that the endometrium regenerates about 400 times during the years that you menstruate.

What is the function of the endometrium?

The endometrium is essential for reproduction. It has three main functions:

• To prepare for a fertilized egg to embed in it (implantation)
• To maintain pregnancy if implantation happens
• To shed and exit your vagina when implantation doesn’t happen (menstruation)

Progesterone and estradiol are the main hormones that control the growth and shedding of your endometrium. The amount of these two hormones changes in a specific way throughout your menstrual cycle. Your ovaries make progesterone and estradiol.

What is the endometrium made of?

Your endometrium has two main layers:

• The basal layer: This lower layer attaches to the smooth muscle tissue of your uterus (myometrium). It doesn’t change much during your menstrual cycle.
• The functional layer: This upper layer changes drastically during your menstrual cycle. It’s what a fertilized egg implants into. And it’s what sheds during your period.

Your endometrium contains:

• Epithelial cells (cells that cover the internal and external surfaces of your body)
• Immune cells
• Stromal cells (a class of connective tissue cells)
• Vascular (blood vessel) cells

When you have your period, the fluid is made up of endometrial cells and blood from blood vessels in your uterus.

How thick is the endometrium?

The thickness of your endometrium varies throughout your menstrual cycle. For a healthy reproductive endometrium, the thickness is typically:

• 12 to 13 millimeters (mm) — about half an inch — during the proliferative phase (before ovulation)
• 16 to 18 mm thick before your period
• 1 to 4 mm thick during your period

After menopause, your endometrium is typically less than 5 mm thick. Your healthcare provider can check the thickness of your endometrium with a transvaginal ultrasound or an MRI.

What happens if the endometrium is too thick?

When your endometrium is too thick, it’s called endometrial hyperplasia. It’s a treatable condition that can cause abnormal menstrual bleeding and infertility. Untreated atypical endometrial hyperplasia can become cancerous.

What are the conditions that affect the endometrium?

Conditions that affect or involve your endometrium include:

• Adenomyosis (tissue similar to your endometrium starts to grow into the muscle wall of your uterus, the myometrium)
• Endometrial cancer (endometrial cells grow out of control)
• Endometrial hyperplasia (abnormally thick endometrium)
• Endometrial polyps (growths in the inner lining of your uterus)
• Endometriosis (tissue similar to your endometrium grows in places other than your uterus)
• Endometritis (inflammation of your endometrium due to infection)

Most of these conditions are treatable or manageable with medication or surgery.

Symptoms that may mean your endometrium isn’t working right

Common symptoms that may signal there’s an issue with your endometrium include:

• Abnormal uterine bleeding
• Heavy menstrual bleeding
• Infertility
• Irregular periods
• Painful menstrual cramps
• Pelvic pain with or without severe cramping

It’s important to see a gynecologist if you’re having any of these symptoms. While these symptoms may be your usual, they’re not medically normal. Know that you don’t have to live with the discomfort that these symptoms can cause.