Uterine Fibroids: What They Are and Why Their Location Changes the Symptoms

Imagine two people being told that an ultrasound has found a fibroid. One has been struggling with increasingly heavy periods, while the other has fairly normal bleeding but feels uncomfortable pressure low in the pelvis and needs to pass urine more often. Their fibroids might even be a similar size. What makes their experiences so different is often where the fibroid is growing.

A uterine fibroid, also called a leiomyoma, is a common, non-cancerous growth that develops from the smooth muscle of the uterus (womb). Some people have just one; others have several. Many cause no symptoms at all and are found by chance during an examination or scan. Finding a fibroid therefore tells us something about the anatomy, but we still need the person's story to understand whether it is causing a problem.

To picture why location matters, it helps to know the layers of the uterus. The endometrium is the lining that changes and sheds during menstruation. Around it sits the myometrium, the thick muscle that contracts during periods and childbirth. A fibroid begins in this muscle. As it grows, it may remain within the wall, push towards the cavity where the endometrium sits, or extend towards the outside of the uterus.

Where the fibroid grows changes what the patient feels

A submucosal fibroid grows towards or into the uterine cavity. It can change the shape of the endometrial surface, so even a relatively small one may be associated with heavy periods. Because it occupies space within the cavity, it can also matter when someone is trying to conceive, although the effect on fertility varies from person to person.

An intramural fibroid sits within the muscular wall. As it becomes larger, the uterus may change shape or increase in size. Depending on its position, it can contribute to heavier bleeding, period pain or a sense of pelvic fullness. A subserosal fibroid grows towards the outside of the uterus. It may have less effect on menstrual bleeding but, if sufficiently large or awkwardly placed, can press on neighbouring structures such as the bladder or bowel. Some fibroids grow on a stalk; these are described as pedunculated.

This is why a scan saying “4 cm fibroid” is only the beginning of the explanation. A 4 cm fibroid projecting into the cavity may cause quite different difficulties from a 4 cm fibroid growing outwards. The report's description of position, whether the uterine cavity is distorted and how many fibroids are present can be just as important as the measurements.

Fibroids are made of bundles of smooth-muscle cells and a collagen-rich supporting matrix. They form a more defined mass than the changes seen in adenomyosis, where tissue similar to the endometrium is found within the muscle wall. Their development is complex: oestrogen, progesterone, local growth signals and genetic changes all play a part. Fibroids are most common during the reproductive years and often shrink after menopause. They are also more common and can present earlier in Black women, but no individual's symptoms should be interpreted on ethnicity alone.

What about the heavy bleeding? A fibroid does not usually bleed into the uterus like an open wound. The mechanisms are more complicated and are not completely understood. Distortion of the cavity, changes to its blood vessels and lining, and altered contraction of the uterine muscle may all contribute. Normally, after the endometrium sheds, uterine contractions and local clotting help limit blood loss. When a fibroid affects those processes, periods can become much heavier. A fibroid mainly growing outwards may leave the cavity relatively undisturbed, so pressure can be the bigger complaint instead.

Pressure symptoms have a more straightforward anatomical explanation. The bladder lies close to the uterus, so an enlarged uterus may leave someone feeling they need to pass urine frequently. Pressure towards the bowel can contribute to constipation or discomfort. The relationship is not automatic, though: urinary frequency, pelvic pain and altered bleeding have other possible causes, and a fibroid found on a scan should not become the explanation for every symptom.

Following the symptoms into the appointment

Now return to the person with heavy periods. They tell you that on some days they avoid leaving home because they are frightened of bleeding through their clothes. They have been getting unusually tired and sometimes feel their heart racing after climbing stairs. The scan shows an intramural fibroid that distorts the uterine cavity. Suddenly, the history, the anatomy and the symptoms begin to fit together.

Repeated heavy blood loss can deplete iron stores and eventually cause iron-deficiency anaemia. That may help explain the fatigue, palpitations, dizziness or breathlessness. But heavy menstrual bleeding matters even when haemoglobin is normal. It can affect work, sleep, relationships and day-to-day confidence. NICE places the effect on quality of life at the centre of its assessment; a patient does not have to prove a particular volume of blood loss before their experience is taken seriously.

In practice, you might ask how long the periods last, how often menstrual products need changing, whether there are clots or flooding, and whether bleeding occurs between periods. Ask about pelvic pain or pressure, possible pregnancy where relevant, medicines and how symptoms affect normal life. If someone reports significant blood loss, it is also worth asking about the symptoms of anaemia rather than waiting for a blood result to tell the whole story.

NICE recommends a full blood count when someone presents with heavy menstrual bleeding. Further tests are guided by the history and clinical assessment; iron studies may be useful in selected circumstances rather than being automatic for every patient. Results help put the symptoms into context, but they do not replace what the person has told you.

For someone whose main complaint is pressure or urinary frequency, the conversation takes a different direction. You would want to know when those symptoms began, whether they are getting worse and what else might account for them. A fibroid growing towards the outer wall could explain the pressure, but urinary or bowel conditions still need consideration. That combination of listening and keeping an open mind is what makes the scan meaningful.

An ultrasound is commonly used to identify fibroids and describe their size, number and position. If the history suggests a submucosal fibroid, a polyp or another problem within the uterine cavity, hysteroscopy may be offered because it allows the clinician to look directly inside that cavity. NICE recommends choosing the initial investigation according to the symptoms and examination, rather than using the same test for everyone.

Persistent bleeding between periods, for example, needs to be explored in its own right. It would be easy to see a known fibroid in the notes and assume the matter is settled, but there may be another cause of the bleeding that requires investigation. The scan result is one part of the assessment, not the whole diagnosis.

Sometimes the team needs a more detailed map before planning treatment. MRI may be considered when ultrasound has not provided enough information about the fibroids' position, number or relationship to surrounding structures, particularly before procedures such as myomectomy or uterine artery embolisation. It is not automatically needed for every patient with fibroids.

What treatment is trying to change

Once the symptoms and anatomy are clear, the treatment conversation becomes easier to follow. For a patient who has a small fibroid and feels well, no treatment may be needed. For someone whose periods are exhausting them, reducing bleeding and treating any anaemia may be the first priority. For someone with substantial pelvic pressure, controlling the bleeding alone may not make much difference if the problem is the bulk of the fibroid.

Treatment also depends on the person's preferences, other health conditions and whether they hope to become pregnant. These details are not an afterthought. Two patients with very similar scan reports might reasonably choose different approaches because they want different outcomes.

Medicines can be useful when heavy bleeding is the main difficulty. Tranexamic acid helps reduce menstrual blood loss by slowing the breakdown of clots. Non-steroidal anti-inflammatory drugs can help with period pain and may also reduce bleeding for some people. Hormonal treatments, including combined hormonal contraception and a levonorgestrel-releasing intrauterine system (LNG-IUS), may help control bleeding, depending on suitability and how much the uterine cavity is distorted. They do not all remove or substantially shrink the fibroid itself.

NICE recommends considering an LNG-IUS as a first treatment for heavy menstrual bleeding when fibroids are smaller than 3 cm and do not distort the cavity, if it is suitable for the patient. Fibroids measuring 3 cm or more may prompt referral for specialist assessment and discussion of other options. That threshold guides decisions about management; it is not a boundary between a safe fibroid and a dangerous one.

For some people with moderate to severe fibroid symptoms, specialist medical treatments that act on reproductive hormones are another option. NICE has recommended selected gonadotrophin-releasing hormone (GnRH) antagonist treatments, including relugolix combination therapy and linzagolix, for eligible patients. These require an individual discussion about benefits, contraindications, monitoring and reproductive plans.

Procedures may be considered when medicines are not enough or the anatomy makes an intervention more suitable. A submucosal fibroid projecting into the cavity can sometimes be removed during hysteroscopy. Myomectomy removes fibroids while retaining the uterus, though fibroids can return and the operation carries risks. Uterine artery embolisation reduces the fibroid's blood supply so it can shrink; the possible effects on future pregnancy need specialist discussion. Hysterectomy removes the uterus and is a definitive treatment for fibroids, but it also means the person will no longer be able to carry a pregnancy.

Notice how we have come back to the same question as at the beginning: what is the fibroid actually doing to this person? If the problem is bleeding, the plan needs to improve bleeding. If the problem is pressure, the treatment needs to address the mass effect. And throughout, the patient's priorities help determine which benefits and trade-offs are acceptable.

What this looks like for a student nurse

You may meet someone with fibroids long before a treatment decision is made, or you may care for them following a procedure. Either way, the most helpful starting point is often a simple conversation about what has changed for them. Has bleeding become difficult to manage? Are they dizzy when standing or breathless walking to the bathroom? Is pressure affecting their sleep? Are they worried about fertility or recovery time? Those answers help you understand what matters alongside the investigation results.

If someone is experiencing substantial bleeding, observe and report concerns such as worsening dizziness, marked breathlessness, palpitations or signs of haemodynamic compromise, and follow the local assessment and escalation process. After a procedure, nursing care includes monitoring pain, bleeding, observations and mobilisation according to the procedure and local guidance. Asking about symptoms, checking the results and recording what the patient hopes treatment will achieve all contribute to safe, person-centred care.

The most useful thing to remember is that a fibroid's position gives meaning to its size. Once you can picture the endometrium, the muscular wall and the structures next to the uterus, it becomes much easier to understand why one patient comes with heavy periods, another comes with pelvic pressure and a third has no symptoms at all.

Related Bleepbook reading: Adenomyosis explores changes within the uterine muscle that can produce similar symptoms, while The menstrual cycle explains what normally happens to the endometrium and hormones during a period.

References

NICE (2018; updated 2021). Heavy menstrual bleeding: assessment and management (NG88). www.nice.org.uk/guidance/ng88.

NICE. Heavy menstrual bleeding: rationale and impact. www.nice.org.uk/guidance/ng88/chapter/rationale-and-impact.

NHS. Fibroids: symptoms, diagnosis and treatment. www.nhs.uk/conditions/fibroids/.

University College London Hospitals NHS Foundation Trust. Fibroids: patient information. www.uclh.nhs.uk/patients-and-visitors/patient-information-pages/fibroids.

Munro, M.G., Critchley, H.O.D., Fraser, I.S. and FIGO Menstrual Disorders Committee (2018). The two FIGO systems for normal and abnormal uterine bleeding symptoms and classification of causes: 2018 revisions. International Journal of Gynecology & Obstetrics, 143(3), 393–408. doi.org/10.1002/ijgo.12666.

NICE (2024). Linzagolix for treating moderate to severe symptoms of uterine fibroids (TA996). www.nice.org.uk/guidance/ta996.

NICE (2022). Relugolix–estradiol–norethisterone acetate for treating moderate to severe symptoms of uterine fibroids (TA832). www.nice.org.uk/guidance/ta832.