An Introduction to Fibroids

This article provides an overview of the symptoms, causes and diagnosis of uterine fibroids. This will be of help to any woman who thinks she may be suffering from this common condition.



Uterine fibroids, which are non-cancerous tumours, occur in up to 77% of women. Although they only cause symptoms in around a quarter of cases they remain the most common cause of hysterectomy before the menopause.

Hysterectomy rates are falling quickly in the United Kingdom as women seek alternatives to radical surgery. In many cases conservative measures can be offered to treat symptoms and avoid hysterectomy. In some cases, however, hysterectomy is still the best option for complete and timely resolution of what can be severely debilitating symptoms for some women.

Although fibroids are one of the most common conditions affecting women we know surprisingly little about them and their natural history. In this article I will outline the facts of which we are aware and dispel some of the myths about fibroids. I will also look at some of the important consequences of having fibroids, as well as discuss some the techniques doctors use to diagnose them.

In the subsequent articles I shall concentrate on the diagnosis and investigation of fibroids and the various options for treatment.These three articles, in combination, are useful for the lay-woman and her family to gain an understanding of the condition and the options for management. There is also an article in this series aimed at medical professionals and the well-informed lay person which goes more deeply into the research and technical aspects of the procedures.

What are fibroids?

Fibroids are benign (non-cancerous) tumours or growths affecting the uterus. The uterus is composed almost entirely of muscle fibres which are not capable of voluntary contraction, but nonetheless contract strongly during childbirth, expelling the baby through the birth canal.

Fibroids are not composed of fibrous tissue at all, but each fibroid appears to grow by clonal replication of a single muscle cell. In other words, a single muscle cell starts to grow and replicate itself many thousands of times over, creating a firm muscular tumour with some associated new blood vessels and supporting tissues within it.  

The normal controlling mechanisms restricting growth and replication of individual cells appear to be lost when a fibroid starts to grow.  It is not clear why this happens, nor why some fibroids grow more rapidly than others and why some women have a greater tendency to develop fibroids than others.  

How are fibroids categorised?

Fibroids are categorised according to their site in the uterus and their relation to the muscular wall of the uterus.

Fibroids that lie in a superficial position where the greater part of their diameter is outside the muscular wall of the uterus are termed subserous fibroids.

Some may even begin to separate away from the uterus on a stalk or pedicle containing the blood vessels which supply blood and nutrients to the fibroid. These are known as pedunculated fibroids. Rarely the fibroid can become attached to other structures in the abdomen such as the bowel or omentum (fatty tissue around the bowel) from which they may develop a blood supply. These pedicle attachments to the uterus can then sometimes become thinner and more tenuous and in some cases may even break off completely allowing the fibroid to become completely detached from the uterus and migrate elsewhere in the abdomen.

Fibroids that have the majority of their diameter within the muscle of the uterus or extend to both the internal and external surfaces of the uterus are called intramural fibroids. Sometimes it is difficult to distinguish between subserous and intramural fibroids, especially with very large fibroids when the outer muscular layer can be stretched very thinly over the surface of the fibroid.

Fibroids that extend predominantly over the internal (endometrial) surface of the uterus are known as submucous fibroids. Where less than 50% extends into the cavity of the uterus they are categorised as Type II, when more than 50% protrudes into the cavity they are called Type I and when they are completely inside the cavity or on an internal stalk they are called Type 0 submucous fibroids.

Who gets fibroids?

Studies have shown that African American women are up to three times more likely to develop fibroids than white, Hispanic or Asian Americans. We know that fibroids are also more common in black women elsewhere in the world, so there appears to be a genetic rather than environmental component determining whether or not women will develop fibroids.  

It is not related to a single gene, but defects of the chromosomes of the cells making up fibroids can be demonstrated in over 50% of cases. Unfortunately we are not yet in a position to predict who will go on to develop fibroids on the basis of genetic testing. 

What controls the growth of fibroids?

Fibroids are sensitive to the ovarian steroid hormones, oestrogen and progesterone. Progesterone seems to be the most import factor in causing the muscular cells to divide, increasing the number of cells in the fibroid, but oestrogen affects the size of the cells. This is why most fibroids tend to shrink when a woman reaches the menopause and oestrogen levels in the blood fall.  

There are other signalling proteins in the body called growth factors which can also determine the rate at which fibroids (and other tissues) grow. Some are more plentiful in women who go on to develop fibroids. However we still know surprisingly little about why some women develop fibroids and why they grow more quickly in some women than in others.

Although many will claim otherwise, there is no convincing evidence that diet or avoidance of any particular dietary components has any effect on whether or not you will develop fibroids. Furthermore, if you do have fibroids there is no known dietary or drug treatment that will make them go away. Some drugs and complementary remedies may improve your symptoms and make it easier to manage with fibroids, but the fibroids, themselves, will not go away.

Can fibroids turn malignant (cancerous)?

In theory, malignant change in a fibroid is possible and has been used as an excuse for removing fibroids in the past. A study in Australia looking at the hospital records of patients at two major teaching hospitals over a 28 year period identified just 48 women with a malignant change in a uterine fibroid. That equates to less than one woman in a million in Australia developing a cancerous fibroid each year.  

We believe the statistics are similar in this country. Therefore, routine removal of fibroids cannot be justified on the basis of avoiding cancer alone. However if a fibroid is growing very rapidly, the possibility of removal should be considered and some of the modern imaging techniques which can detect specific features suggestive of a potential malignancy should be employed.

How do I know that I have fibroids?

Fibroids are so common that they develop in up to 77% of women. Many women do not know that they have them as probably only a quarter of fibroids will cause symptoms. There is no need to worry about fibroids unless they start to cause symptoms. If you do develop some of the symptoms listed below you should see your doctor who will examine you and organise an ultrasound scan in the first instance. Or, your doctor may refer you directly to a gynaecologist who can perform a scan for you and discuss what treatment, if any, is required.

What symptoms can fibroids cause?

Fibroids can cause a variety of symptoms. Often the onset is insidious, as they tend to grow slowly and you may not notice that there has been any deterioration until they are quite large.  

Perhaps the most common symptom is heavy and painful menstruation, typically caused by submucous and intramural fibroids. Sometimes there are cramps as the uterus tries to expel the fibroid with painful contractions. Larger subserous fibroids tend to cause local pressure symptoms leading to pain when opening the bowels or passing urine. The sheer size of these fibroids can cause abdominal distension and bloating.  In addition, pressure on the bladder can lead to increased frequency of passing urine. 

Submucous and intramural fibroids can cause a delay in conception and increased risk of miscarriage. All fibroids can cause complications during pregnancy, such as placental separation (abruption), premature delivery, obstructed labour and painful degeneration of the fibroid.

What investigations should I have?

The first line investigation is a careful history to determine what problems or potential problems you have encountered to help to guide in management. An internal examination will usually demonstrate enlargement of the uterus. Confirmation of the size, site and number of fibroids can usually be obtained by performing an ultrasound scan

If your periods have been heavy it is sensible to perform a full blood count to check your haemoglobin in case you have become anaemic. It is also sensible to perform a blood coagulation screen, particularly if surgery is under consideration, in case you have a tendency to bleed excessively or your blood has a tendency to clot more strongly putting you at risk of thrombosis.

Sometimes an ultrasound scan is not conclusive, especially if your fibroids are very large, or if the endometrium is not distinct. A magnetic resonance (MR) scan is very useful in these cases.

Based on the results of these basic investigations, an experienced gynaecologist can help you to decide which is the right treatment option for you. We shall explore these options and look at methods of diagnosis more fully in the next articles.

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The part of the body that contains the stomach, intestines, liver, gallbladder and other organs. Full medical glossary
Relating to the abdomen, which is the region of the body between the chest and the pelvis. Full medical glossary
Placental lining separates from the uterus. Full medical glossary
Not dangerous, usually applied to a tumour that is not malignant. Full medical glossary
The organ that stores urine. Full medical glossary
A fluid that transports oxygen and other substances through the body, made up of blood cells suspended in a liquid. Full medical glossary
A common name for the large and/or small intestines. Full medical glossary
Abnormal, uncontrolled cell division resulting in a malignant tumour that may invade surrounding tissues or spread to distant parts of the body. Full medical glossary
Malignant, a tumour that may invade surrounding tissues or spread to distant parts of the body. Full medical glossary
The basic unit of all living organisms. Full medical glossary
Structures in the cell nucleus that carry genetic information. Full medical glossary
Blood that has coagulated, that is, has moved from a liquid to a solid state. Full medical glossary
A combination of laboratory tests designed to assess the blood clotting quality of blood. Full medical glossary
A condition that is linked to, or is a consequence of, another disease or procedure. Full medical glossary
The fertilisation of an ovum by a sperm cell: the start of pregnancy. Full medical glossary
The process of determining which condition a patient may have. Full medical glossary
Relating to the endometrium. Full medical glossary
The layer of tissue lining the uterus. Full medical glossary
One of the three main food constituents (with carbohydrate and protein), and the main form in which energy is stored in the body. Full medical glossary
A benign tumour, most often in the uterus. Full medical glossary
Benign tumours, most often in the uterus. Full medical glossary
The basic unit of genetic material carried on chromosomes. Full medical glossary
Relating to the genes, the basic units of genetic material. Full medical glossary
A chemical that stimulates new cell growth and maintenance in the body. Full medical glossary
The oxygen carrying pigment that is present in red blood cells. Full medical glossary
A substance produced by a gland in one part of the body and carried by the blood to the organs or tissues where it has an effect. Full medical glossary
The surgical removal of the uterus (womb). Full medical glossary
An element present in haemoglobin in the red cells. Full medical glossary
A large abdominal organ that has many important roles including the production of bile and clotting factors, detoxification, and the metabolism of proteins, carbohydrates and fats. Full medical glossary
Describes a tumour resulting from uncontrolled cell division that can invade other tissues and may spread to distant parts of the body. Full medical glossary

The time of a woman’s life when her ovaries stop releasing an egg (ovum) on a monthly cycle, and her periods cease

Full medical glossary
The shedding of the lining of the uterus (period), as part of the female reproductive cycle. Full medical glossary
The spontaneous loss of pregnancy. Full medical glossary
Tissue made up of cells that can contract to bring about movement. Full medical glossary
A hormone involved in female sexual development, produced by the ovaries. Full medical glossary
relating to the ovaries Full medical glossary
Attached to or supported on a stalk (peduncle). Full medical glossary
A craving to eat non-food substances such as earth or coal. Full medical glossary
The organ that nourishes the embryo during pregnancy and also eliminates waste. Full medical glossary
the period from conception to birth Full medical glossary
Compounds that form the structure of muscles and other tissues in the body, as well as comprising enzymes and hormones. Full medical glossary
The process by which DNA makes copies of itself when a cell divides. Full medical glossary
The formation of a blood clot. Full medical glossary
A group of cells with a similar structure and a specialised function. Full medical glossary
An abnormal swelling. Full medical glossary
A diagnostic method in which very high frequency sound waves are passed into the body and the reflective echoes analysed to build a picture of the internal organs – or of the foetus in the uterus. Full medical glossary
The process of using high-frequency sound waves to produce internal images of the body. Full medical glossary
The womb, where embryo implantation occurs and the growing foetus is nourished. Full medical glossary