The FIGO Classification System: Understanding Your Fibroid's Location

When you look at an ultrasound or MRI report, you may see your fibroids assigned a number from 0 to 8. This is the FIGO classification system, a standardized “mapping” tool used by doctors worldwide to describe exactly where a fibroid is located within the uterus ^[1].

In the world of fibroids, location is highly important, though size, cavity distortion, and the number of fibroids all play a role in your symptoms. A small fibroid inside the uterine lining can sometimes cause severe bleeding, while a large outer fibroid might primarily cause pressure ^[2][3]. Understanding your FIGO type helps you and your doctor decide which treatment is most likely to work for you.

The FIGO Scale: A Map of the Uterus

The uterus has three main layers: the endometrium (the inner lining where a period comes from), the myometrium (the thick muscle wall), and the serosa (the thin outer skin). The FIGO system numbers fibroids based on which of these layers they touch or inhabit ^[4][5].

1. Submucosal Fibroids (The “Inner” Layer: Types 0, 1, 2)

These fibroids grow just under or into the uterine lining (the cavity). They are the most likely to cause menorrhagia (heavy menstrual bleeding) ^[3].

• Type 0: Completely inside the uterine cavity, often attached by a small stalk (pedunculated).
• Type 1: Mostly inside the cavity, but less than 50% of the fibroid extends into the muscle wall.
• Type 2: At least 50% of the fibroid is buried in the muscle wall, with the rest bulging into the cavity.

Impact: These types are common culprits for heavy bleeding and infertility, as they “distort” the cavity where an embryo would implant ^[6][3]. Because they are accessible from the inside, Types 0-2 are often removed through the vagina and cervix by hysteroscopy when technically suitable, though a large or deeply embedded Type 2 may require staged or non-hysteroscopic approaches ^[7].

2. Intramural Fibroids (The “Middle” Layer: Types 3, 4)

These grow entirely within the muscular wall of the uterus ^[4].

• Type 3: 100% of the fibroid is in the muscle wall, but it is so close that it actually touches the inner lining.
• Type 4: 100% of the fibroid is in the muscle, not touching the inner or outer layers.

Impact: Type 3 fibroids are “hybrids” in terms of symptoms; while they are in the wall, their contact with the lining can still cause heavy bleeding ^[3]. Type 4 fibroids primarily cause the uterus to enlarge, leading to “bulk” symptoms like pressure or a visible enlargement of the abdomen ^[8].

3. Subserosal Fibroids (The “Outer” Layer: Types 5, 6, 7)

These grow on the outer surface of the uterus ^[4].

• Type 5: More than 50% of the fibroid is in the muscle wall, but it bulges out from the surface.
• Type 6: Less than 50% of the fibroid is in the muscle; most of it is on the outside.
• Type 7: Attached to the outside of the uterus only by a stalk (pedunculated).

Impact: While they do not often cause heavy bleeding directly because they are far from the lining ^[9], they can still contribute to bleeding if there are other coexisting issues. Instead, they frequently cause bulk symptoms: pressing on the bladder (frequent urination), the rectum (constipation), or nerves (back pain) ^[8][10].

4. The “Others” (Type 8 and Hybrids)

• Type 8: Fibroids in unusual locations, such as the cervix or the ligaments holding the uterus in place ^[4].
• Hybrid Types (e.g., Type 2-5): These are transmural fibroids. They are large enough to stretch all the way from the inner lining, through the muscle wall, to the outer surface ^[11]. These often require more complex surgical planning because they affect every layer of the uterus ^[12].

Why the FIGO Number Matters for Your Care

Your doctor uses these numbers to build your surgical or treatment roadmap ^[1].

• Fertility: If you are trying to conceive, doctors focus heavily on Types 0, 1, 2, and 3, because cavity-distorting fibroids have the strongest link to miscarriage and implantation failure ^[6][13].
• Surgical Route: Route decisions cannot be made from the FIGO number alone; surgical expertise, fibroid size, and number all play a role ^[12][14].
• Bleeding Risk: Size is not a perfect predictor of blood loss. Identifying the FIGO type ensures the doctor evaluates which specific fibroid is causing your symptoms.