The majority of women with fibroids have uncomplicated pregnancies. But fibroids can interact with pregnancy in ways that are worth understanding clearly — both to reduce anxiety from vague information and to know what specific risks deserve monitoring.
How Common Is This?
Fibroids are present in 2–12% of pregnancies, with many discovered incidentally on first-trimester ultrasound. Most of these findings represent small or well-positioned fibroids that carry minimal obstetric risk. The anxiety a fibroid finding generates in pregnancy is often disproportionate to the actual risk profile for that specific fibroid.
How Pregnancy Affects Fibroids
The high estrogen and progesterone environment of pregnancy can cause unpredictable fibroid behaviour. Approximately 50–60% remain stable in size. Around 22–32% grow — predominantly in the first trimester. A smaller percentage shrink, particularly in the third trimester. Growth that occurs tends to slow after the first trimester as hormonal levels stabilise. Most fibroids that grow during pregnancy regress significantly postpartum.
Risks by Fibroid Type
Submucosal fibroids carry the highest obstetric risk — associated with higher miscarriage risk and may contribute to preterm labour. Small ones may be removed before trying to conceive. See our article on submucosal fibroids explained.
Large intramural fibroids may increase risk of preterm labour, placental abruption, and caesarean section due to fetal malpresentation. Fibroids over 5–6cm warrant closer monitoring through pregnancy.
Subserosal fibroids generally carry the lowest risk — they do not contact the cavity and typically do not affect the fetus unless very large.
Fibroid Degeneration in Pregnancy
The most common painful complication. As fibroids rapidly expand blood supply in early pregnancy, some outgrow their supply and undergo degeneration — sudden, localised, intense pain with tenderness over the fibroid site, sometimes with low-grade fever. Managed with rest and paracetamol. Uncomfortable but not usually dangerous to the pregnancy. Can last days to 2 weeks before resolving. See our article on fibroid pain causes for distinguishing degeneration from other pain patterns.
What Good Monitoring Looks Like
If you have fibroids and are pregnant: confirm fibroid size, type, and location at first-trimester ultrasound. Ensure follow-up scanning is planned if fibroids are significant. Discuss delivery planning explicitly — whether a fibroid near the lower uterine segment or cervix could obstruct labour. Be explicit with your obstetric team that you have fibroids and want the monitoring plan to account for them specifically. For the broader fertility and preconception picture, see our article on trying to conceive with fibroids.
Read next If you want to understand the hormonal side of this, how estrogen drives fibroid growth — and what shifts it.