Finding out you have fibroids during pregnancy — or discovering you are pregnant while already managing fibroids — triggers understandable anxiety. The reassuring starting point: the majority of women with fibroids go through pregnancy without significant complications. But the risks that do exist are real, depend heavily on fibroid type and location, and are worth understanding clearly.
How Common Is This?
Fibroids are present in 2–12% of pregnancies, though the true figure is likely higher since many are never detected. Many women discover fibroids for the first time on a routine first-trimester ultrasound — a finding that is common enough to be fairly standard practice to investigate. In the majority of these cases, the fibroids are small or in positions that pose minimal obstetric risk, and the pregnancy proceeds normally with monitoring.
How Pregnancy Affects Fibroids
The high estrogen and progesterone environment of pregnancy can cause fibroids to behave unpredictably. Studies show that approximately 50–60% of fibroids remain stable in size during pregnancy. Around 22–32% grow — predominantly in the first trimester. A smaller percentage actually shrink. The growth that occurs tends to slow or stop after the first trimester as the hormonal surge stabilises.
Predicting which fibroids will grow is currently not possible from baseline characteristics alone. The most practical approach is regular ultrasound monitoring — typically more frequent during the first and second trimesters if fibroids are known.
Risks By Fibroid Type and Location
Risk level varies significantly by fibroid position:
Submucosal fibroids carry the highest obstetric risk. Those distorting the uterine cavity are associated with higher miscarriage risk, particularly in the first trimester. They may also contribute to preterm labour and fetal malpresentation (baby in an awkward position) as pregnancy progresses.
Intramural fibroids carry intermediate risk. Large ones (over 5cm) or those that distort the cavity are more concerning than small ones that do not. The research on intramural fibroids and pregnancy outcomes is less consistent than for submucosal fibroids — some studies show increased risk, others do not, with cavity distortion being the key variable.
Subserosal fibroids generally carry the lowest obstetric risk. They do not contact the uterine cavity and typically do not affect the fetus directly. Very large subserosal fibroids can occasionally cause mechanical complications, but these are uncommon.
Specific Complications That Can Occur
Miscarriage: Particularly associated with submucosal fibroids that distort the cavity. The fibroid physically interferes with implantation and early placental development.
Placenta previa: When the placenta implants over or near the cervical opening. Fibroids can limit where the placenta can implant, increasing this risk.
Placental abruption: Separation of the placenta from the uterine wall before delivery. More common with fibroids, possibly related to the disrupted uterine wall structure.
Preterm labour: Fibroids can trigger early uterine contractions. This is more likely when fibroids are large or multiple.
Caesarean section: Higher rates of C-section in women with fibroids, partly due to fetal malpresentation (the fibroid limiting the baby’s ability to rotate head-down) and partly due to impaired uterine contractions during labour.
Fibroid degeneration: The most common painful complication. When a fibroid outgrows its blood supply, it undergoes painful degeneration — typically a localised area of acute pelvic pain with tenderness, sometimes fever. Managed with rest and paracetamol. Uncomfortable but not usually dangerous to the pregnancy.
Postpartum haemorrhage: Elevated risk because fibroids can prevent the uterus from contracting normally after delivery, impairing the mechanism that closes off blood vessels at the placental site.
What Good Monitoring Looks Like
If you have fibroids and are pregnant, the minimum reasonable monitoring includes: documentation of all fibroid sizes, types, and locations at the first-trimester ultrasound; follow-up ultrasound(s) to reassess growth and position; a plan for third-trimester assessment of fetal position relative to any fibroids near the cervix or lower segment; and a delivery plan that accounts for any elevated risk factors specific to your situation.
Be explicit with your midwife or obstetrician that you have fibroids and want your monitoring plan to account for them. This sounds obvious but fibroids found incidentally are not always flagged clearly in ongoing maternity notes.
After Delivery
Many fibroids shrink significantly postpartum as hormone levels drop. Some women find their fibroid symptoms are substantially reduced after completing their family. This is worth keeping in mind if you have been delaying treatment decisions: the postpartum period provides a natural reassessment point with updated imaging. For more on fibroids and fertility planning, see our article on fibroids and infertility.
