Uterus

The uterus is a hollow, pear-shaped organ in the female reproductive system. It’s where a fertilized egg implants and grows into a fetus. The lining of your uterus, called the endometrium, sheds during your period.

Your uterus is an organ that plays a key role in reproduction. Learning about its functions can help you better understand your body. A gynecologist or obstetrician can help diagnose and treat conditions related to your uterus.

What is the function of a uterus?

Your uterus plays a key role in your reproductive health. The four main jobs of your uterus involve aiding:

• Menstrual cycles: Your uterine lining sheds during your period (menstruation). When you feel period cramps, it’s your uterus squeezing to shed this tissue.
• Fertility: A fertilized egg typically implants in your uterus after conception. This step is needed for pregnancy to continue.
• Pregnancy: Your uterus stretches as the fetus grows during pregnancy. The placenta attaches to your uterus to deliver nutrients from you to the fetus through the umbilical cord.
• Labor and delivery: During labor, your uterus contracts (squeezes) regularly to help open up your cervix. These contractions also help push your baby through your vagina.

What are the parts of a uterus?

Parts of your uterus include:

• Fundus: The fundus is the uppermost and widest part of your uterus. It connects to your fallopian tubes. It’s usually the most muscular part of your uterus. Providers check the positioning of your fundus, called fundal height, during pregnancy and after birth.
• Corpus: This is the main body of your uterus. It’s where a fertilized egg typically implants during pregnancy.
• Isthmus: The isthmus is the part of your uterus between your corpus and cervix. It’s where your uterus starts to narrow.
• Cervix: The cervix is the lowest part of your uterus. Your cervix opens to your vagina.

Your uterus also consists of three layers of tissue:

• Perimetrium: This is the outermost, protective layer. It’s made of epithelial cells.
• Myometrium: This is the highly muscular middle layer. It’s what expands during pregnancy and contracts to push your baby out.
• Endometrium: This is the inner layer or lining of your uterus (uterine lining). It sheds during your period.

Where is it located?

Your uterus sits in the space in your pelvis between your bladder and rectum. The following tissues help keep your uterus in place:

• Pelvic floor muscles
• Perineal body (the central tendon of your perineum)
• Ligaments in your pelvis, lower back and hips

Uterus positions

A uterus can have several different positions in your body. The most common position is anteverted. This is when your uterus tilts forward toward your bladder.

If you don’t have an anteverted uterus, you might have a:

• Retroverted uterus: This is a common variation where your uterus tilts backwards towards your rectum. About 20% to 25% of women have a retroverted uterus. It’s also called a “tilted” or “tipped” uterus.
• Anteflexed uterus: This is a common variation where your uterus is angled or “bent” forward towards your bladder.
• Retroflexed uterus: Your uterus is bent backward towards your rectum.
• Midposition uterus: This is when your uterus is positioned straight up and down, pointing towards your head.

What does it look like?

When you see a diagram of your uterus head-on, it looks like a light bulb or an upside-down pear. If you look at a side view of your uterus, it resembles a kidney bean.

How big is it?

If you’re not pregnant, your uterus is about the size of your fist or a lemon. It’s about 3 inches long and 2 inches wide. It’s about 1 inch thick.

During pregnancy, your uterus stretches. It can grow to the size of a watermelon. Your uterus shrinks down to its regular size and position over about six weeks postpartum. This process is called involution.

How much does it weigh?

In a non-pregnant state, your uterus weighs around 1 ounce (28 grams). At the end of the third trimester of pregnancy, it can weigh up to 2 pounds (almost 1 kilogram).

What are the common conditions of the uterus?

Several health conditions can affect your uterus. Some include:

• Adenomyosis: Endometrial tissue grows into the muscle of your uterus
• Asherman’s syndrome: Scar tissue in your uterus
• Endometriosis: Uterine lining tissue grows in places other than your uterus
• Pelvic inflammatory disease: An infection of your reproductive organs
• Uterine cancer: Cancer of your uterus, like endometrial cancer or uterine sarcoma
• Uterine factor infertility: Trouble getting pregnant due to uterine problems
• Uterine fibroids: Small, noncancerous tumors in your uterus
• Uterine polyps: Growths in the endometrial lining of your uterus
• Uterine prolapse: Pelvic floor muscles and ligaments weaken, causing your uterus to sag
• Uterine rupture: Tearing of your uterus

Uterine abnormalities

Some people are born with different-shaped uteruses. Some uterine abnormalities include:

• Bicornuate uterus: You have a heart-shaped uterus with two separate uterine horns rather than a single cavity.
• Arcuate uterus: A small, shallow indentation forms at the top of your uterine cavity. It ranges from mild to severe.
• Septate uterus: A membrane divides your uterus into two parts.
• Unicornuate uterus: You have one fallopian tube and an irregularly shaped uterus.
• Didelphys uterus: You have two uteruses.

These differences may also affect your fallopian tubes, cervix and upper vagina. They may cause infertility or pregnancy complications.

People with Mayer-Rokitansky-Küster-Hauser syndrome have underdeveloped or absent uteruses.

Common symptoms of uterine issues

Symptoms that can suggest there’s an issue with your uterus include:

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

Reach out to a gynecologist if you have these symptoms.