Fibroids in Pregnancy

Read on to learn about fibroids in pregnancy

What is a fibroid?

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A uterine fibroid is a benign, firm, usually roundish, swelling (tumour) that develops within the muscular wall of the uterus (womb). A fibroid can vary in size from being as tiny as a pea to as large as a melon. Fibroids are very common. The figures quoted vary, but it is estimated that between 25 per cent and 80 per cent of women have a fibroid or fibroids if you look very carefully. In a typical case a woman will have several fibroids present within her uterus and these will usually be of varying sizes. Fibroid tumours are benign (they are not cancerous and do not spread to other parts of the body). They usually cause no symptoms at all and are often present without a woman knowing that she has them. If they become larger then they are more likely to result in symptoms or problems such as pain or discomfort. If fibroids enlarge and distort the endometrium (lining of the womb) then they cause heavy periods.

Having a fibroid during pregnancy and the potential problems it can cause.

Gynaecologists in the past used to be concerned that a fibroid may grow quickly due to the rising oestrogen levels in pregnancy and cause major problems. Recent medical research has shown that most fibroids do not actually become larger during pregnancy, and those that do often return to their pre-pregnancy size afterwards.

However, there are several ways that a fibroid may affect a pregnancy.

A uterine fibroid can cause uncomfortable feelings of discomfort, pressure, heaviness or even pain if they grow larger and press on surrounding organs or pelvic structures. A fibroid may lead to sharp pain in the lower back (lumbar region) and legs if there is pressure on a nerve.

Read about how to shrink fibroids naturally

Red degeneration of a fibroid during pregnancy

A rare complication of a fibroid during pregnancy is a problem known medically as red degeneration. If red degeneration occurs there is haemorrhage within the centre of the fibroid. This usually happens in the middle trimester (three months) of pregnancy and is thought to result from the leiomyoma (fibroid tumour) growing rapidly and outgrowing its blood supply. Red degeneration can be very painful, usually requires treatment with strong painkillers, but nearly always settles down without causing serious problems or needing specific treatment.

With regard to falling pregnant, fibroids are thought to account for about two to three per cent of all infertility problems. If a fibroid or fibroids develop just under the endometrium (surface lining of the uterus) this may affect the way in which a fertilised egg attaches or implants in the endometrium of the womb. A fibroid therefore, may cause recurrent early miscarriage, which is often so early that a woman is not even aware that she has been pregnant.

More rarely a fibroid may obstruct the canal of the cervix or the opening of the fallopian tubes into the womb. Sometimes later in pregnancy, fibroids may also disrupt the normal development and growth of the uterus, leading to premature labour and childbirth. Extremely rarely, fibroids may lead to a miscarriage before 23 weeks of pregnancy.

The most frequent problem with fibroids in pregnancy is that they can lead to slightly early labour and delivery of the baby two to three weeks early, which is of very little threat to the baby. Rarely a fibroid can develop and enlarge in the lower part of the uterus and lead to cause partial blockage of the birth canal. If this happens, then a caesarean section operation is usually necessary to deliver the baby.

When a woman who is having infertility problems is discovered have uterine fibroids, they may be treated and removed they are sufficiently large, to try and increase the likelihood of conception. Gynaecologists usually advice that small fibroids are best left untreated. Medical research has indicated that if there is cause found for the fertility problem, treating and removing the fibroids increases the chance of falling pregnant by about 40% to 80%.

In more detail

Fibroids are very common. It is estimated that between 25 and 80% of all women have uterine fibroids. Therefore many women who are pregnant will have a fibroid or fibroids. Many women who are trying to fall pregnant will have fibroids. It is easy to diagnose fibroids with ultrasound scanning, and most pregnant women have one or more ultrasound examinations. Before the advent of ultrasound scanning many women who were pregnant did not know that they had fibroids. Nowadays many women are diagnosed with fibroids during pregnancy.

If you have been diagnosed with a fibroid that is causing no symptoms and want to fall pregnant, then it is usually safe to continue to try to conceive. I would advise that you discuss your fibroid with your family doctor or gynaecologist if you are trying to fall pregnant. If you want to start a family or try to fall pregnant it is sensible to discuss this with your GP or gynaecologist anyway. This is because pre-conception counselling can improve the chances of having a healthy baby.

Uterine fibroids usually grow during pregnancy. Some fibroids will stay the same size and some may even shrink during pregnancy. If you are pregnant and a fibroid is diagnosed, it is quite likely that it has been present for some time, many months or even many years.

If you are having difficulty falling pregnant or if you have had recurrent miscarriages, then investigation is important. Gynaecologists recommend that a couple, without risk factors for infertility, that has been trying to conceive for a year or more, should have tests for infertility.

If a couple is known to have factors that make infertility more likely, then most doctors will advise that a gynaecology opinion is sought after 6 months of trying to conceive. The most common reason for earlier assessment is if the woman is 35 years old or older. Other factors include a woman having irregular periods or a man who has a history of chemotherapy.

If you are known to have fibroid or fibroid symptoms then it is advisable to seek investigation after 6 months of trying to conceive.

The problems of fibroids in pregnancy

A Fibroid or Fibroids are very often discovered in the womb (uterus) during a pelvic examination or more frequently during a routine ultrasound scan when a woman is pregnant. Medical research has shown that the most uterine fibroids do not grow or shrink during pregnancy. It has been found that about a third of fibroids may enlarge during the first three months (known medically as the first trimester) of pregnancy. Studies have shown that the vast majority of women with fibroids have an uncomplicated pregnancy and childbirth. However it has been found that some women do unfortunately have some problems due to their fibroids. It is known that uterine fibroids are linked to a greater rate of spontaneous miscarriage, placental abruption, early onset of childbirth (preterm labour), malpresentation of the baby (abnormal position of the baby e.g. breech baby), an abnormal or difficult childbirth( labour dystocia), need for caesarean section and bleeding after the baby is born (postpartum haemorrhage).

Fibroids (leiomyomas) are benign (non-cancerous) tumours or swellings made up of uterine smooth muscle which develop in the muscular wall of the womb. They are very common. By the time they are 35 years of age it is estimated that 40-60% of women will have at least one fibroid, and by the time they reach the age of 50 approximately 70-80% will have fibroids. The exact cause of fibroids is still unknown. Making the diagnosis of fibroids during pregnancy is neither simple nor straightforward.

Research has shown that only 42% of fibroid greater than 5cm (labelled as large) and 12% of smaller fibroids (measuring 3-5 cm) can be felt and diagnosed on pelvic examination. Surprisingly, making the diagnosis using ultrasound is also difficult. This is mainly because of the difficulty of distinguishing fibroids from the normal thickening of the lining of the womb (myometrium). It is therefore thought likely by specialists that the frequency of fibroids during pregnancy is actually underestimated.

There is an increasing trend in the Western world for pregnancy to be delayed until women are older. Research has shown that the incidence of uterine fibroids in older women who are having medical treatment for infertility is approximately 12-25%.

Even though they are becoming more common, the exact nature and reasons for leiomyomas causing infertility and problems when a woman is pregnant are not fully understood.

Medical evidence from ultrasound studies which monitored the size of fibroids during pregnancy has shown that most fibroids (60-78%) did not change in size significantly throughout pregnancy. The volume of fibroids was monitored prospectively. Some fibroids did grow (22-32%) and increased in volume and most of this growth took place in the first three months of pregnancy. In particular most growth occurred during the first 10 weeks of pregnancy and it is interesting to note that very little growth took place during the last 6 months of pregnancy (i.e. during the second and third trimesters).

The vast majority of fibroids cause no symptoms. A well described, but rare complication of fibroids is known as “red degeneration”. This is most likely to happen to a pedunculated subserosal fibroid. Red degeneration causes severe localised abdominal pain. Fibroids can also cause pain simply due to their size and larger fibroids (those greater than 5cm) are those that most often cause pain, usually during the second and third trimesters of pregnancy. In fact pain is the most common complication of fibroids during pregnancy.

A study investigated the frequency of red degeneration in fibroids during pregnancy using ultrasound scans. It was found that 9% of fibroids had ultrasound evidence (showed a heterogeneous echogenic pattern or cystic change) of red degeneration. The women were asked about their symptoms and about 70% of these women had experienced severe abdominal pain compared with about 12% of women whose ultrasound scans showed no sign of red degeneration in their fibroids.

Why does red degeneration cause pain?

There are three medical hypotheses which have been proposed to explain why red degeneration of a fibroid causes severe pain.

  1. The first theory is that the rapid speed of growth of the fibroid causes the tissue in the middle of the fibroid to outgrow its blood supply resulting in death of the tissue (known as infarction).
  2. The second theory is that the growing uterus disrupts the blood supply to the fibroid by kinking the blood vessels in some way (there is thought to be a change in the architecture of the blood vessels). This happens even if the fibroid does not grow.
  3. The third theory is that the pain is due to prostaglandin chemicals produced by damage of the cells in the fibroid. This theory is supported by the fact that NSAIDS drugs (such as ibuprofen or diclofenac) which work by inhibiting prostaglandin quickly and effectively control the pain.

Effect of Fibroids on Pregnancy

Outcome It has been found that between 10% and 30% of women with fibroids have problems or complications during their pregnancy. However, medical specialists have criticised the way that some of these studies have been carried out. (They have commented that there have been problems such as: selection bias, small and differing characteristics of the populations studied, low occurrence of adverse outcomes, varying inclusion criteria and inadequate confounding variables.) The studies carried out so far have found varying and inconsistent correlations between fibroids and the frequency of complications in pregnancy. More research into fibroids during pregnancy needs to be carried out.

It is not known yet precisely how fibroids cause complications in pregnancy. It is hypothesised that mechanical obstruction or impaired distensibility (stretchability) of the uterus may explain some of the problems caused by fibroids.

Early Pregnancy


It is known that the frequency of spontaneous miscarriage is increased in pregnant women who have fibroids. One study found that the rate of miscarriage in women with fibroids was 14% compared with 7% in women without fibroids. Research has found that the size of a fibroid does not affect the risk of miscarriage, but that the number of fibroids may do. Multiple fibroids increase the risk of miscarriage (miscarriage rate found to be 23%) compared with a single fibroid (miscarriage rate was 8%). It is also thought that the position of the fibroid in the uterus is important. Early spontaneous miscarriage happens more often when the fibroids are in the main body of the uterus when compared with fibroids being in the lower segment of the uterus or those fibroids which are intramural or submucosal. It is not known exactly how fibroids cause miscarriage. Possible mechanisms include: increased irritability of the uterus, mechanical compression by the fibroid and/or damage to the blood supply to the growing placenta or foetus.

Bleeding in early pregnancy

The risk of bleeding during early pregnancy is affected by the location of the fibroid in the womb. If the placenta has implanted close to where the fibroid is then the risk of bleeding is increased significantly to 60% from a risk of 9% if there is no contact between the fibroid and the placenta.

Late Pregnancy

Preterm labour and preterm premature rupture of membranes

Uterine fibroids increase the risk of premature labour and childbirth. The risk of preterm labour when fibroids are present is 16% in contrast with a risk of 8% when no fibroids are present. The rate of preterm delivery is 16% in contrast with a risk of 11% when there are no fibroids present.

Having multiple fibroids and having fibroids that are in direct contact with the placenta have been shown to be independent risk factors for premature onset of labour.

It is interesting that fibroids are not an independent risk factor for preterm premature rupture of the membranes (PPROM) of the amniotic sac around the baby. In fact recent research has suggested that fibroids may actually decrease the risk of PPROM.

Placental abruption

Data from medical studies suggests that placental abruption is three times as common in those women who have fibroids during pregnancy. Independent risk factors for placental abruption are: submucosal fibroids, retroplacental fibroids and fibroids with a volume of >200 cm3.

A study which looked retrospectively found that placental abruption occurred in 57% of women who had retroplacental fibroids, in contrast with 2.5% of women who had fibroids in other areas of their womb. It is thought that one way that fibroids make placental abruption more likely is that there is reduced blood flow to the fibroid and the surrounding uterine tissue. This then leads to reduced blood flow (partial ischemia) and decidual necrosis in the tissue of the placenta over the underlying leiomyoma.

Placenta praevia

Only 2 research papers have been published about the relationship between placenta praevia and fibroids. They both indicated that the rate of placenta praevia is doubled even when adjustments were made for previous surgical procedures such as myomectomy and caesarean section.

Foetal abnormalities (anomalies) and foetal growth retardation

Medical research has found that the growth of the baby is not affected by the existence of uterine fibroids. Studies have suggested that women with fibroids were slightly at greater risk of having a baby whose growth had been slowed, these studies were not adjusted for gestational age of the foetus or the age of the mother, and these studies have been criticised by specialists in this area. A large fibroid or fibroids can rarely press on and distort the cavity of the uterus and may then lead to a foetal abnormality. The congenital abnormalities that have been shown to occur with large submucosal fibroids include: torticollis ( an abnormal twisting of the neck), dolichocephaly (lateral compression of the baby’s skull) and limb reduction defects.

Labour and Delivery

Malpresentation, caesarean section and labour dystocia

The rate of malpresentation of the foetus in women with fibroids is 13% in contrast with a rate of 4.5% in women with no fibroids. Independent risk factors for malpresentation are multiple fibroids, large fibroids and fibroids in the lower uterine segment.

Many medical studies have found that having a uterine fibroid increases the risk of caesarean section. A systematic review discovered that having fibroids increased the rate of caesarean section by a factor of 3.7 (from 13.3% - no fibroid to 48.8% - fibroids present). This is partly due to an increase in labour dystocia. Predisposing factors for caesarean section are: multiple fibroids, foetal malpresentation, large fibroids, submucosal fibroids and leiomyomas in the lower uterine segment.

However, obstetricians usually advise that the presence of uterine fibroids is not a contra-indication to a trial of labour.

Postpartum haemorrhage

Medical evidence and studies have provided conflicting data about the rate of postpartum haemorrhage (bleeding), however pooled cumulative figures have suggested that the rate of haemorrhage following childbirth is greater in those women who have uterine fibroids (risk – 2.5%) when compared with women with no fibroids (risk – 1.4%).

A fibroid may distort the architecture of the womb and also interfere with contractions of the uterine muscle (myometrium) leading to loss of muscle strength (atony) of the uterus and postpartum haemorrhage. These factors may also explain why fibroids increase the rate of hysterectomy in the weeks following childbirth (during the puerperium).

Retained placenta

A medical study has shown that the rate of retained placenta of the uterus is more frequent in those women who had a fibroid, but only if it was located in the lower segment of the womb. But pooled cumulative data has suggested that the risk of having retained placenta is more frequent in all women with leiomyomas regardless of the position of the fibroid (1.4% - fibroid present - compared with 0.6%- no fibroid present).

Uterine rupture following myomectomy

This is complication is extremely rare. One study looked at 120 women who had a baby at term having had a previous abdominal myomectomy (in which the uterine cavity was not entered) and there were no cases of uterine rupture. It is uncertain whether the same is true with laparoscopic myomectomy. Researchers report that there are many case reports of uterine rupture occurring during childbirth in women who had previously had a laparoscopic myomectomy. Recent research has shown that uterine ruptures take place before the start of labour at the site of the previous myomectomy carried out by laparoscope. Fortunately the risk of uterine rupture following laparoscopic myomectomy is reported to be low at 0.5% to 1%.

The management of fibroid complications in pregnancy

The management of fibroid pain during pregnancy

The management of fibroid pain during pregnancy depends on the severity of the pain. Mild pain requires just simple painkillers like paracetamol. More severe pain requires assessment by a doctor and following any necessary investigations is usually managed conservatively with bed rest, hydration and analgesics. Sometimes doctors will prescribe prostaglandin synthetase inhibitors like non-steroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen or diclofenac.

It is important to note that medications which are prostaglandin synthetase inhibitors (such as NSAIDs like ibuprofen, diclofenac, naproxen and indomethacin) should be used with care (especially if taken for more than 2 days) in the third trimester. This is because these drugs are known to be linked with potential side-effects on the foetus and newborn infant. These side-effects include: pulmonary hypertension, premature closure of the foetal ductus arteriosus, intracranial bleeding and oligohydramnios.

If pain is very severe then stronger painkillers (such as opiates) may be needed, or other methods of providing analgesia may be utilised such as epidural analgesia.

Rarely surgical treatment such as myomectomy may be needed.

Myomectomy as a treatment for fibroids and pregnancy

In those women who have had a fibroid diagnosed before they fall pregnant, gynaecologists may consider surgical treatment such as myomectomy. However, it is not clear whether myomectomy does improve the chances of falling pregnant or whether it affects positively the perinatal outcomes.

It is rare for leiomyomata to be operated on in the first 4-5 months of pregnancy. Several studies have looked at the safety aspects of carrying out a myomectomy on a woman who is pregnant during the first and second trimesters (i.e in the first 6 months of pregnancy).

Obstetricians advice that acceptable reasons for performing a myomectomy during pregnancy include: a fibroid undergoing red degeneration and causing pain that cannot be controlled (particularly if the fibroid is pedunculated or subserosal), a very large or rapidly growing fibroid or any large (greater than 5cm in size) leiomyoma present in the lower segment of the uterus. Researchers have studied the health of the baby and health problems of the mother in women who have had a myomectomy and compared these with women who were looked after and treated without surgery on their fibroid. They found that there was no significant difference in neonatal and obstetric outcomes. However, those women who had had a myomectomy in pregnancy were more likely to have a lower segment caesarean section because the doctors were concerned about the risk of rupture of the uterus.

With regard to carrying out a myomectomy to remove a fibroid when a caesarean section is performed, most obstetricians agree that this is not advisable. This is because of the well documented risks of severe bleeding problems (necessitating blood transfusion, uterine artery ligation and/or hysterectomy). It is advised that myomectomy should only be carried out at the time of a caesarean section if this is unavoidable to allow the safe delivery of the baby or to allow closure of the hysterotomy (incision in the womb). Obstetric consultants agree that it is generally safe to remove pedunculated subserosal fibroids during a caesarean section without there being an increased risk of bleeding.

Uterine artery embolization (UAE)

Interventional consultant radiologists have been carrying out bilateral uterine artery embolization for many years. More recently UAE has become a treatment for large symptomatic fibroids in those women who are not pregnant and who, most importantly, do not wish to become pregnant in the future. A recent medical study found that UAE that was performed straight after a caesarean section in women with leiomyomata may be an effective means of reducing bleeding after childbirth and reducing the need for myomectomy or hysterectomy by causing shrinkage of the leiomyomata. There are several reports of successful and uncomplicated pregnancies following UAE for fibroids, but generally pregnancy is not advisable following a uterine artery embolization.


Fibroids are very common in women of reproductive age. Most fibroids do not grow (or become smaller) in pregnancy, but about 30% may enlarge during the first three months of pregnancy. The results from studies are somewhat conflicting, but it is reassuring to note that the majority of women with uterine fibroids will have uncomplicated pregnancies and childbirth.

Uterine fibroids are linked to an increased rate of spontaneous miscarriage, preterm labour, foetal malpresentation, placental abruption, labour dystocia, caesarean section and postpartum haemorrhage.

The most frequent complication of a fibroid in pregnancy is pain. The symptoms can generally be managed with conservative treatment (i.e. surgery is not required), but very rarely surgical treatment is necessary. A caesarean section may be advisable for those women who have previously had a myomectomy, especially if the cavity of the womb was opened.

Those women who have previously had a myomectomy should probably have a caesarean section performed before labour starts, especially if the cavity of the uterus was opened. Uterine artery embolization is a reasonable alternative treatment option to surgery in the event of fibroids causing severe problems, but UAE is absolutely contra-indicated during pregnancy and in those women who wish to fall pregnant in the future.

Learn how to shrink fibroids naturally