Educational guide
Endometrium: Anatomy, Function & Conditions
Locations: AdvertisementAdvertisement The endometrium (uterine lining) is essential for reproduction. It’s what a fertilized egg implants into. It’s also what sheds during your period. Certain health conditions involve your endometrium, like endometriosis and
This guide cannot diagnose a condition or recommend a personal treatment plan. Discuss medical questions with a qualified professional.
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The endometrium (uterine lining) is essential for reproduction. It’s what a fertilized egg implants into. It’s also what sheds during your period. Certain health conditions involve your endometrium, like endometriosis and endometrial hyperplasia.
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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.
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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.
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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.
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
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When you have your period, the fluid is made up of endometrial cells and blood from blood vessels in your uterus.
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.
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.
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.
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.
The endometrium is a dynamic tissue that’s key to your reproductive health. Any abnormalities with your period could be a sign that there’s an issue with your endometrium. It’s always a good idea to see your healthcare provider if you’re having period issues. They can recommend tests to check the health of your endometrium.
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Cleveland Clinic’s health articles are based on evidence-backed information and review by medical professionals to ensure accuracy, reliability and up-to-date clinical standards.
Cleveland Clinic’s health articles are based on evidence-backed information and review by medical professionals to ensure accuracy, reliability and up-to-date clinical standards.
- Ang CJ, Skokan TD, McKinley KL. Mechanisms of Regeneration and Fibrosis in the Endometrium (https://pubmed.ncbi.nlm.nih.gov/37843929/). Annu Rev Cell Dev Biol. 2023;39:197-221. Accessed 7/29/2025.
- Critchley HOD, Maybin JA, Armstrong GM, Williams ARW. Physiology of the Endometrium and Regulation of Menstruation (https://pubmed.ncbi.nlm.nih.gov/32031903/). Physiol Rev. 2020;100(3):1149-1179. Accessed 7/29/2025.
- Deryabin PI, Borodkina AV. The Role of the Endometrium in Implantation: A Modern View (https://pubmed.ncbi.nlm.nih.gov/39273693/). Int J Mol Sci. 2024;25(17):9746. Accessed 7/29/2025.
- Giri SK, Nayak BL, Mohapatra J. Thickened Endometrium: When to Intervene? A Clinical Conundrum (https://pmc.ncbi.nlm.nih.gov/articles/PMC8310815/). J Obstet Gynaecol India. 2021;71(3):216-225. Accessed 7/29/2025.
- The Female Reproductive System. In: Mescher AL, eds. Junqueira's Basic Histology: Text and Atlas. 17th ed. McGraw-Hill; 2024. Accessed 7/29/2025.
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