Fibroids in Pregnancy

Being told you have fibroids at your first scan

Many women learn they have fibroids for the first time at a pregnancy scan, having had no symptoms at all. The NHS notes that "sometimes, fibroids can be found during other tests or scans, such as a pregnancy scan".

Fibroids are benign growths of the muscle of the uterus. ACOG describes them as "benign (not cancer) growths that develop from the muscle tissue of the uterus", also called leiomyomas or myomas, and "the most common type of growth found in a woman's pelvis". Their size range is wide: ACOG notes they "can range in size from small, pea-sized growths to large, round ones that may be more than 5 to 6 inches wide", and that there "may be only one fibroid or many of varying sizes".

NICE Clinical Knowledge Summaries lists the risk factors as "increasing age (until the menopause); early menarche; older age at first pregnancy; comorbidities such as obesity and hypertension; black and Asian ethnicity; family history". Fibroids are substantially more common in Black women, and ACOG notes they "seem to occur at a younger age and grow more quickly in Black women", adding that "these differences may be due to racism and inequities in society, which can increase the risk of health problems".

What pregnancy does to a fibroid

Fibroids are hormone-responsive, so the general expectation is that some grow during pregnancy, particularly in the first half, and that many then stabilise. ACOG notes that outside pregnancy a fibroid "may remain very small for a long time and suddenly grow rapidly, or grow slowly over a number of years" — unpredictability is characteristic of them.

Growth by itself causes no symptoms in most pregnancies. Where fibroids do cause trouble, position matters more than size: a fibroid in the wall of the uterus behaves differently from one on a stalk on the outer surface or one bulging into the cavity.

Red degeneration, and why the pain is so sudden

This is the complication most likely to bring you to hospital. When a fibroid grows faster than its blood supply, the tissue inside it begins to break down. The result is sudden, severe, localised abdominal pain, often with tenderness directly over one spot, sometimes with a low-grade temperature and a raised white cell count. It typically happens in the second trimester.

It is alarming and it is usually self-limiting. Management is conservative: rest, fluids, and pain relief suitable for pregnancy, with the pain usually settling over several days to a couple of weeks. Discuss pain relief with your team rather than self-medicating, because some over-the-counter anti-inflammatory painkillers are not suitable in pregnancy.

The important thing is that severe abdominal pain in pregnancy always needs assessing rather than self-diagnosing as fibroid pain. Placental abruption, appendicitis, a torted ovarian cyst and a urinary infection can all present similarly, and only assessment separates them.

What fibroids can affect, and how often

NICE CKS lists "obstetric complications" among the potential complications of fibroids, alongside iron deficiency anaemia from heavy bleeding, bladder and bowel compressive symptoms, subfertility, and torsion of a pedunculated fibroid.

In practice, the associations discussed in pregnancy are with the baby lying in an unusual position, with a raised chance of caesarean birth where a fibroid sits low in the uterus and blocks the way out, and with heavier bleeding after birth because a uterus containing fibroids may not contract down as efficiently. Most women with fibroids have none of these.

Anaemia is worth watching specifically. Many women with fibroids enter pregnancy with depleted iron stores after years of heavy periods. NICE CKS defines anaemia in pregnancy as haemoglobin below 110 g/L, noting a level of 105 g/L "appears adequate in the second and third trimesters". If your iron was low before pregnancy, say so at booking.

Why they are not removed while you are pregnant

Surgery to remove fibroids during pregnancy is avoided except in rare and specific circumstances, because a pregnant uterus has a dramatically increased blood supply and the bleeding risk is serious. This includes at caesarean section: removing fibroids during a caesarean is not routine practice, and is avoided in most situations for the same reason.

The same logic applies to treatments used outside pregnancy. Uterine artery embolisation and the medicines used to shrink fibroids are not options during pregnancy, and the NHS treatment options for fibroids are framed around non-pregnant care. Fibroid treatment is a conversation for after birth.

Birth planning

Having fibroids does not by itself mean a caesarean. What matters is where they are. A fibroid low in the uterus, in the path the baby would take, is the one that changes the plan; fibroids higher up in the wall of the uterus often do not.

Ask specifically where your fibroids are, whether any is in the lower segment, and whether that changes the recommended mode of birth. If you have had fibroids removed in a previous operation, tell your team, because whether the cavity of the uterus was opened during that surgery affects birth planning.

Because of the raised chance of heavier bleeding after birth, expect active management of the third stage and, in some units, a plan for extra measures to be immediately available. That is precaution rather than prediction.

After birth

Fibroids commonly shrink after pregnancy as hormone levels fall, and NICE CKS notes they "typically develop in women of reproductive age and regress after the menopause". A fibroid that caused problems in this pregnancy does not automatically do so in the next, and it is worth a gynaecology review a few months after birth if symptoms persist.