Fibroids Explained
Understanding Uterine Fibroids: What They Are, Why They Develop and How They Can Affect Your Health
Introduction
Being told you have fibroids can be unsettling.
Perhaps they were discovered during a routine scan, while investigating heavy periods, or as part of fertility investigations. Whatever led to your diagnosis, it's natural to have questions.
"What exactly are fibroids?"
"Are they cancer?"
"Will they keep growing?"
"Will they stop me having children?"
The reassuring news is that fibroids are extremely common. In fact, many women have them without ever knowing. They are almost always benign, meaning they are not cancer, and many never cause symptoms or require treatment.
However, for some women, fibroids can significantly affect quality of life. Depending on their size and where they develop within the uterus, they may cause heavy menstrual bleeding, pelvic pain, pressure on nearby organs or fertility problems.
Understanding fibroids begins with understanding the uterus itself. Once you know how the womb normally works, it's much easier to understand what fibroids are and why they sometimes cause symptoms.
In this article, we'll explain what fibroids are, why they develop, how they affect the body and why every woman's experience is different.
Quick Summary
Fibroids are benign (non-cancerous) growths that develop from the muscle of the uterus.
They are extremely common, affecting up to 70–80% of women by the age of 50, although many never develop symptoms.
Fibroids vary enormously in size, number and location.
Some women never know they have fibroids, while others experience heavy periods, pelvic pain or fertility problems.
Fibroids are influenced by female hormones, particularly oestrogen and progesterone.
Most fibroids are not dangerous and many require no treatment.
Why Understanding Fibroids Matters
Hearing the word "growth" or "tumour" can be frightening.
Many women immediately worry about cancer.
Fortunately, fibroids are almost always benign.
Understanding this distinction can remove a great deal of unnecessary anxiety.
It's also important to understand that not all fibroids behave the same way.
A tiny fibroid inside the cavity of the womb may have a much greater effect on fertility than a much larger fibroid growing on the outside of the uterus.
Likewise, one woman may have several large fibroids and no symptoms at all, while another has a single small fibroid that causes heavy bleeding.
The size of a fibroid isn't always the most important factor.
Its location often matters far more.
What Are Fibroids?
Fibroids are growths made from the same smooth muscle tissue that forms the wall of the uterus.
Rather than being a foreign lump that develops inside the womb, a fibroid is more like an area where some of the normal muscle cells begin multiplying more than they should.
Imagine the uterus as being made of tightly woven muscle fibres.
If one small group of those muscle cells starts growing more rapidly than the surrounding tissue, it gradually forms a firm, rounded lump.
That lump is a fibroid.
Because fibroids grow from the uterine muscle itself, they remain attached to the uterus, although some develop on narrow stalks called peduncles.
Fibroids can be as small as a pea or become large enough to distort the shape of the uterus.
Most women develop more than one fibroid during their lifetime.
How the Uterus Normally Works
To understand why fibroids cause symptoms, it helps to understand how the uterus normally functions.
The uterus is a remarkable muscular organ.
Its walls are made of smooth muscle called the myometrium, which has two important jobs.
During pregnancy, the muscle stretches dramatically to accommodate a growing baby.
During labour, those same muscle fibres contract powerfully to help deliver the baby.
The inside of the uterus is lined by the endometrium, which thickens each month in preparation for pregnancy before being shed during menstruation if pregnancy doesn't occur.
Fibroids develop within the muscle layer, but depending on where they grow, they may press into the uterine cavity, remain within the wall itself or project outwards from the surface of the uterus.
Their position largely determines the symptoms they cause.
Different Types of Fibroids
One of the reasons fibroids affect women so differently is that they can grow in several different locations.
Intramural Fibroids
These develop within the muscular wall of the uterus.
They are the most common type and may enlarge the uterus or contribute to heavy menstrual bleeding.
Submucosal Fibroids
These grow just beneath the lining of the uterus and bulge into the uterine cavity.
Although often smaller than other fibroids, they are the type most likely to cause heavy bleeding and fertility problems because they distort the space where an embryo would normally implant.
Subserosal Fibroids
These grow on the outer surface of the uterus.
Rather than affecting menstrual bleeding, they are more likely to cause pressure symptoms if they become large enough to press on nearby organs such as the bladder or bowel.
Pedunculated Fibroids
Some fibroids develop on a narrow stalk, either inside or outside the uterus.
These are known as pedunculated fibroids and may occasionally twist on their stalk, causing sudden pain.
Why Do Fibroids Develop?
Despite being so common, we still don't know exactly why fibroids develop.
Researchers believe they arise from a combination of genetic, hormonal and environmental factors.
Fibroids are particularly influenced by the female hormones oestrogen and progesterone.
These hormones stimulate normal uterine muscle growth during the reproductive years, but they also appear to encourage fibroids to grow.
This helps explain why fibroids are uncommon before puberty, often grow during the reproductive years and usually shrink after menopause, when hormone levels naturally fall.
Genetics also play a role.
Women with a close family member who has fibroids are more likely to develop them themselves, suggesting inherited factors influence susceptibility.
How Big Can Fibroids Become?
Fibroids vary enormously in size.
Some are so small they can only be detected on ultrasound.
Others become large enough to enlarge the uterus to the size of a pregnancy.
Doctors may describe fibroids using measurements in centimetres or compare the size of the uterus with the number of weeks of pregnancy, such as saying it is "the size of a 16-week pregnancy."
Although large fibroids often attract attention, size alone doesn't determine how troublesome they are.
A small fibroid inside the uterine cavity can sometimes cause more symptoms than a much larger fibroid growing harmlessly on the outside of the uterus.
Why Do Fibroids Cause Symptoms?
Many women have fibroids without experiencing any symptoms at all.
When symptoms do occur, they usually result from one of three things:
Distortion of the uterus, affecting the lining of the womb or the shape of the cavity.
Pressure on nearby organs, such as the bladder or bowel.
Changes in blood supply and muscle function, which can contribute to heavy menstrual bleeding and pain.
Exactly which symptoms develop depends largely on where the fibroid is growing.
Are Fibroids Cancer?
This is one of the biggest fears women have after diagnosis.
The answer is reassuring.
Almost all fibroids are benign.
A very rare cancer called a leiomyosarcoma develops from the muscle of the uterus, but current evidence suggests it usually develops independently rather than from an existing fibroid.
In other words, having fibroids does not mean they will "turn into cancer."
Your doctor may recommend further investigations if a fibroid behaves unusually or grows rapidly after menopause, but for the vast majority of women, fibroids remain completely benign.
Why Every Woman's Experience Is Different
Fibroids are incredibly variable.
One woman may have a single fibroid that never changes throughout her life.
Another may develop several fibroids that gradually increase in size over many years.
Some women experience heavy bleeding.
Others mainly notice pelvic pressure.
Many never realise they have fibroids until they undergo a scan for an unrelated reason.
This variation explains why treatment must always be tailored to the individual rather than the fibroid alone.
Looking Ahead
Being diagnosed with fibroids doesn't automatically mean you'll need treatment.
Many fibroids can simply be monitored over time.
If symptoms develop, there are many effective treatments available, ranging from medication to minimally invasive procedures and surgery.
The right option depends on your symptoms, the size and location of the fibroids, your age and whether you hope to have children in the future.
Understanding your fibroids is the first step towards deciding whether treatment is needed and, if so, which approach is likely to be most suitable.
Key Takeaways
Fibroids are benign growths that develop from the muscle of the uterus.
They are extremely common and often cause no symptoms.
Their location is usually more important than their size.
Fibroids are influenced by oestrogen and progesterone and usually shrink after menopause.
Having fibroids does not mean you have cancer.
Many women never need treatment, while others have a wide range of effective treatment options available.
Frequently Asked Questions
Can fibroids disappear on their own?
Fibroids don't usually disappear completely during the reproductive years, but they may stop growing or shrink. After menopause, many fibroids become smaller as oestrogen and progesterone levels fall naturally.
Can stress cause fibroids?
There is no good evidence that stress directly causes fibroids. They are thought to develop because of a combination of genetic and hormonal factors. However, living with symptoms such as heavy bleeding or chronic pain can certainly be stressful.
If my mother had fibroids, will I get them too?
Having a close relative with fibroids increases your risk, but it doesn't mean you will definitely develop them. Genetics appear to play an important role, but they're only part of the picture.
Do all fibroids need to be removed?
No. Many fibroids never cause symptoms and can simply be monitored. Treatment is usually recommended only if fibroids are causing significant symptoms, affecting fertility or growing in a way that requires further investigation.
References
This article should be supported by evidence from:
National Institute for Health and Care Excellence (NICE)
Royal College of Obstetricians and Gynaecologists (RCOG)
European Society of Human Reproduction and Embryology (ESHRE)
American College of Obstetricians and Gynecologists (ACOG)
Peer-reviewed research on uterine fibroids, hormone biology and reproductive health.