General Information
Know your Uterus!

Know your Uterus!

How does your uterus work?

Your uterus plays a critical role in menstruation, fertility, and pregnancy. The uterus is a pear-shaped organ and for individuals who are not pregnant, it is only around three inches long and two inches wide – though the exact size will vary from person to person. During pregnancy, this amazing organ can increase to the size of a watermelon and will sit just underneath your ribs – expanding to more than 500 times its original size![1]

Understanding your uterus

The corpus is the main body of the uterus. It’s very muscular and can stretch to accommodate a developing foetus. The uterine wall is made up of three layers; the endometrium, the myometrium and the perimetrium.[2]


The corpus is lined by a mucus membrane called the endometrium. This membrane responds to reproductive hormones by changing its thickness during each menstrual cycle. If an egg is fertilised, it attaches to the endometrium. If no fertilisation occurs, the endometrium sheds its outer layer of cells, releasing them during menstruation.[3]

The myometrium is the thick, middle, muscular layer. This layer expands throughout pregnancy to create space for a growing baby and contracts during labour and delivery. [2]

The perimetrium is a protective outer serous layer of the uterus. This serous layer secretes a lubricating fluid that helps to reduce friction. [2]

What happens to your uterus during menstruation?

The lining of your uterus goes through several changes throughout your menstrual cycle. Your period is the result of the endometrial lining shedding, which happens every cycle unless pregnancy occurs.[4]

For some, this lining is thicker than average, which results in heavy menstrual bleeding.[5]

What happens to your uterus during pregnancy?

The uterus is the only organ that can create a whole other organ. Once pregnant, the uterus expands as the baby grows. The placenta is grown within the uterus to nourish the growing baby, who is connected to the mother through the umbilical cord – which is attached to the uterine wall.[6]

During labour, the muscular walls of the uterus contract to help push the baby through the cervix and vagina. In the following weeks after birth, the uterus shrinks to its pre-pregnancy size.[2]

Learn more about periods and heavy bleeding by visiting #BeBloodyConfident. Heavy bleeding can impact both physical and mental health, so if you are concerned about your menstrual cycle, please seek advice from your GP. Use our resources to help get the conversation started.



[1]- The Science Behind the ‘Mom Bod’: Permanent and Temporary Changes Caused byPregnancy. [online] Available at: [last accessed26/06/2023]

[2]- Cleveland clinic (2022). Uterus: Anatomy, Function, Size, Position & Conditions. [online]Cleveland Clinic. Available at:[last accessed 26/06/2023]

[3]- Cornforth, T. (2020). The Role the Endometrium Plays in Your Reproductive Health.[online] Verywell Health. Available at: [last accessed 26/06/2023]

[4]- NHS (2019). Overview – Periods. [online] NHS. Available at: [last accessed 26/06/2023]

[5]- NHS Choices (2019). Overview – Heavy periods. [online] NHS. Available at: [last accessed 26/06/2023]

[5]- Mayo Clinic. (n.d.). Know the role the placenta plays in pregnancy. [online] Available at: depth/placenta/art-20044425#:~:text=The%20placenta%20attaches%20to%20the. [lastaccessed 26/06/2023]

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