Fibroids During Pregnancy: What You Need to Know

Fibroids and Pregnancy

Being diagnosed with fibroids during pregnancy can be worrying, but it is an extremely common finding. Fibroids are detected in an estimated 2 to 12 per cent of pregnancies on routine ultrasound scans, and the vast majority of women with fibroids go on to have healthy, uncomplicated pregnancies. Understanding what to expect can help alleviate unnecessary anxiety. For more background on fibroids, visit our fibroids information page.

How Do Fibroids Behave During Pregnancy?

The behaviour of fibroids during pregnancy is somewhat unpredictable. Fibroids are sensitive to hormones, particularly oestrogen and progesterone, both of which increase significantly during pregnancy. As a result:

• Some fibroids grow — approximately one-third of fibroids increase in size during pregnancy, most commonly during the first trimester. Growth is usually modest, and most fibroids do not exceed 25 per cent of their pre-pregnancy size.
• Some fibroids stay the same — many fibroids show no significant change throughout pregnancy.
• Some fibroids shrink — a small proportion of fibroids may actually decrease in size during pregnancy.

After delivery, fibroids that grew during pregnancy typically return to their pre-pregnancy size within three to six months as hormone levels normalise.

Potential Complications

While most pregnancies with fibroids proceed without significant problems, fibroids can occasionally cause complications. The risk depends on the size, number, and location of the fibroids:

Pain (Red Degeneration)

One of the most common fibroid-related complications during pregnancy is acute pain caused by red degeneration. This occurs when a growing fibroid outstrips its blood supply, causing the tissue to become ischaemic. It typically presents as sudden, severe, localised pain in the abdomen, often accompanied by a low-grade fever and nausea. Red degeneration most commonly occurs in the second trimester and is managed conservatively with rest, fluids, and pain relief.

Miscarriage

The risk of miscarriage is slightly elevated in women with fibroids, particularly if the fibroids are submucosal (growing into the uterine cavity) or if there are multiple large fibroids. However, the absolute increase in risk is relatively small.

Preterm Labour

Large fibroids or multiple fibroids may increase the risk of preterm delivery. This is thought to be related to the fibroids causing uterine irritability or reducing the space available for the growing baby.

Placental Problems

Fibroids located near the placental implantation site may increase the risk of placental abruption (premature separation of the placenta) or placenta praevia (where the placenta lies low in the uterus, covering the cervix).

Malpresentation and Obstructed Labour

Large fibroids in the lower part of the uterus may physically prevent the baby from moving into the normal head-down position for delivery, or may obstruct the birth canal. In these cases, a planned caesarean section is usually recommended.

Management During Pregnancy

The general approach to fibroids during pregnancy is conservative — that is, treatment of fibroids themselves is avoided during pregnancy unless absolutely necessary. The focus is on monitoring and managing any symptoms or complications that arise:

• Regular monitoring — your obstetric team will monitor fibroid size and position throughout pregnancy using ultrasound scans
• Pain management — if pain occurs (as in red degeneration), it is managed with rest and pregnancy-safe painkillers such as paracetamol
• Delivery planning — if fibroids are large or positioned near the cervix, your obstetric team will plan the safest mode of delivery, which may involve a caesarean section

Surgical removal of fibroids (myomectomy) during pregnancy is almost never recommended due to the risk of significant bleeding. In extremely rare circumstances, surgery may be considered, but this is the exception rather than the rule.

After Pregnancy

Once you have delivered and recovered, if your fibroids were causing significant symptoms before pregnancy or have grown substantially, it is worth discussing treatment options with a specialist. This is particularly important if you are planning another pregnancy, as treating symptomatic fibroids between pregnancies can reduce the risk of complications in future pregnancies.

If you have fibroids and are pregnant or planning a pregnancy, our specialist team can offer advice and reassurance. Book a consultation at the North London Fibroid Clinic to discuss your individual situation.