Uterine fibroids are the most common tumors found in the uterus, and most people who have them go on to deliver healthy babies. But fibroids do raise the odds of certain pregnancy complications, from preterm birth and cesarean delivery to placental problems and postpartum bleeding, with the severity depending heavily on where the fibroids sit, how many there are, and how large they grow. Understanding these risks helps you and your care team make better decisions before, during, and after pregnancy.
How Common Fibroids Are in Pregnancy
Fibroids affect a large share of people of reproductive age. Estimates vary depending on how they are detected, but roughly a quarter of those who menstruate experience symptoms from fibroids at some point. Rates also differ sharply by race and ethnicity. A large study within an integrated U.S. health care system found that Black patients were diagnosed with fibroids at about three times the rate of White patients, while South Asian, East Asian, Southeast Asian, and Hispanic patients also had elevated rates.1JAMA Network Open. Uterine Fibroid Diagnosis by Race and Ethnicity in an Integrated Health Care System Because fibroids are so common, many people discover them for the first time at their initial prenatal ultrasound, which can understandably cause anxiety. The good news is that most fibroids stay quiet throughout pregnancy and require no special treatment.
Where a Fibroid Sits Matters More Than Whether You Have One
Not all fibroids carry the same risks. Their location within the uterus is the single biggest factor in determining whether they will cause trouble. There are three main types based on position: submucosal fibroids grow into the uterine cavity, intramural fibroids sit within the muscular wall, and subserosal fibroids grow outward from the uterus toward the abdominal cavity.
Submucosal fibroids are the most problematic for both fertility and pregnancy. They are associated with lower conception rates, higher miscarriage risk, and more obstetric complications. Removing them before pregnancy has been shown to improve pregnancy rates.2PubMed Central. Uterine Fibroids and Infertility A multicenter cohort study found that a single submucosal fibroid increased the odds of late miscarriage nearly fivefold, while fibroids in other locations did not show a statistically significant link to late pregnancy loss.3PubMed. Association of uterine fibroids with late miscarriage: multicenter cohort study
Subserosal fibroids, on the other hand, do not appear to affect fertility outcomes, and removing them before pregnancy offers no clear benefit.4PubMed Central. Uterine Fibroids and Infertility Intramural fibroids fall somewhere in the middle. They seem to reduce fertility to some degree, and fibroids five centimeters or larger in the uterine wall are linked to higher rates of miscarriage, preterm labor, and cesarean delivery.5International Journal of Current Pharmaceutical Review and Research. Impact of Uterine Fibroids on Fertility and Pregnancy Outcomes: A Prospective Observational Study Recommendations about whether to surgically remove intramural fibroids before trying to conceive remain unsettled, and the decision usually depends on size, symptoms, and individual circumstances.
Do Fibroids Raise Miscarriage Risk?
This is one of the first fears people have after learning about fibroids, and the answer is more reassuring than you might expect. A prospective cohort study that initially found a modest association between fibroids and miscarriage saw that link disappear entirely after adjusting for age, race, and other factors. Age turned out to be doing most of the heavy lifting in the unadjusted numbers, because people who are older are both more likely to have fibroids and more likely to miscarry.6American Journal of Epidemiology. Prospective Cohort Study of Uterine Fibroids and Miscarriage Risk
The exceptions, as noted above, are submucosal fibroids and having multiple fibroids. Women with more than one fibroid had about two and a half times the odds of late miscarriage compared to those without fibroids.7PubMed. Association of uterine fibroids with late miscarriage: multicenter cohort study So the blanket statement “fibroids cause miscarriage” is misleading. A single fibroid that is not poking into the uterine cavity does not appear to meaningfully raise the risk.
How Fibroids Change During Pregnancy
Pregnancy hormones, especially estrogen and progesterone, tend to make fibroids grow. A longitudinal ultrasound study tracked fibroids throughout pregnancy and found that about 71% increased in size between the first and second trimesters, with a slightly lower percentage continuing to grow into the third trimester.8PubMed. Uterine myomas during pregnancy: a longitudinal sonographic study This growth is driven largely by the hormonal environment of pregnancy and the increased blood supply to the uterus.
The flip side is encouraging. After delivery, the hormonal shift reverses, and most fibroids shrink substantially. Research has found that over 70% of women who gave birth saw their fibroids shrink by more than half in volume within three to six months postpartum.9PubMed Central. Postpartum factors and natural fibroid regression A study of Black African women found that about 83% of fibroids decreased in size during postpartum uterine involution.10eCommons@AKU. A prospective characterization of postpartum changes in uterine fibroid volume among black African women Interestingly, using progestin-based contraception after delivery was associated with less fibroid shrinkage, while breastfeeding and other hormonal methods did not seem to make a difference.11PubMed Central. Postpartum factors and natural fibroid regression
Red Degeneration and Pain During Pregnancy
Pain is the most common complication fibroids cause during pregnancy, and the culprit is usually something called red degeneration. This happens when a fibroid grows faster than its blood supply can keep up, and the tissue at its center starts to die. It sounds alarming, and it can be intensely painful, but it is not dangerous to the pregnancy in most cases. Red degeneration is most common in fibroids larger than five centimeters and tends to occur in the second and third trimesters.12PubMed Central. Contemporary Management of Fibroids in Pregnancy
In one study of 113 pregnant women with fibroids, about 9% showed ultrasound changes consistent with red degeneration, and 70% of those women experienced severe abdominal pain, compared with only about 12% of women whose fibroids looked unchanged on ultrasound.13PubMed Central. Contemporary Management of Fibroids in Pregnancy The pain likely comes from the release of prostaglandins as cells break down within the fibroid, which is why ibuprofen and similar anti-inflammatory drugs can be effective at controlling it.
Treatment during pregnancy is conservative: rest, fluids, and pain medication. Anti-inflammatory drugs like ibuprofen can help, but prolonged use beyond 48 hours in the third trimester carries risks for the fetus, including premature closure of a critical blood vessel, so these medications are used cautiously and for short stretches.14PubMed Central. Contemporary Management of Fibroids in Pregnancy – Section: Effect of Uterine Fibroids on Pregnancy Management Acetaminophen is the safer first-line option, and most episodes of red degeneration resolve on their own within a week or two.
Obstetric Complications Linked to Fibroids
A large meta-analysis pooling data across many studies found that, after adjusting for other risk factors, fibroids were independently linked to several adverse outcomes: preterm birth, cesarean delivery, placenta previa, placental abruption, postpartum hemorrhage, intrauterine fetal death, breech presentation, and preeclampsia.15PubMed Central. The influence of uterine fibroids on adverse outcomes in pregnant women: a meta-analysis That is a long list, but context matters. The absolute increase in risk for most of these outcomes is modest for small, well-positioned fibroids. Multiple fibroids and large fibroids are where the risks climb more steeply.
Placental complications deserve special mention. Fibroids can physically distort the uterus in ways that increase the chances of the placenta attaching in an abnormal location (placenta previa) or separating prematurely from the uterine wall (placental abruption). These risks are driven mainly by the mechanical influence of large or numerous fibroids.16PubMed. Uterine Fibroids and Pregnancy: How Do They Affect Each Other? Fibroids can also push the baby into an unusual position, such as breech, because they take up space and change the shape of the uterine cavity.
Delivery and the Cesarean Question
One of the most consistent findings across fibroid-and-pregnancy research is a higher cesarean delivery rate. A retrospective cohort study found that fibroids roughly doubled the odds of fetal malpresentation and increased the odds of cesarean delivery by about 50% even after adjusting for other factors.17PubMed Central. Association of uterine fibroids with adverse pregnancy outcomes: a retrospective cohort study The reasons are intuitive. A fibroid sitting low in the uterus can physically block the birth canal, making vaginal delivery difficult or impossible.18PubMed Central. A Case of an Obstructed Delivery by a Large, Lower Uterine Segment Fibroid Interlocked with a Fetal Mentum Fibroids in the lower uterine segment are particularly associated with higher cesarean rates and with retained placenta after delivery.19PubMed Central. Do Large Uterine Fibroids Impact Pregnancy Outcomes?
Having fibroids does not automatically mean you will need a cesarean. Many people with fibroids deliver vaginally without complications. Your care team will typically assess fibroid size and position in the third trimester and help you plan accordingly. If a large fibroid is sitting right over the cervix, a planned cesarean is the safer bet. If fibroids are elsewhere, a vaginal delivery remains very much on the table.
Postpartum Hemorrhage
Postpartum hemorrhage, or heavy bleeding after delivery, is one of the more serious fibroid-related risks. The same cohort study mentioned above found that women with fibroids had nearly five times the odds of postpartum hemorrhage compared to those without, and submucosal fibroids in particular carried a 77% risk of this complication.20PubMed Central. Association of uterine fibroids with adverse pregnancy outcomes: a retrospective cohort study The mechanism involves how the uterus contracts after the placenta detaches. Normally, the criss-crossing muscle fibers of the uterine wall clamp down on blood vessels like a natural tourniquet. Fibroids embedded in this muscle wall disrupt that architecture, so the uterus cannot contract as effectively, leading to heavier bleeding.
This is why your delivery team will be especially watchful for hemorrhage if fibroids are present. Medications that help the uterus contract, manual uterine massage, and in severe cases surgical intervention are all part of the plan. Knowing about the risk in advance allows the team to prepare, which dramatically improves outcomes.
Surgery During Pregnancy
Removing fibroids while pregnant (a procedure called myomectomy) is generally avoided because of the risks of heavy bleeding and disrupting the pregnancy. But in rare cases, a fibroid causes such severe pain or grows so rapidly that conservative management fails. Among 622 pregnant patients with fibroids in one center’s experience, about 2% required surgical intervention for complications that did not respond to rest and medication. In 92% of those cases, the surgery was successful and the pregnancy continued to term.21Human Reproduction. Successful myomectomy during pregnancy
A systematic review of published data on myomectomy during pregnancy concluded that the procedure appears safe in carefully selected cases when conservative management has failed, though it stressed that thorough counseling about risks is essential beforehand.22PubMed. Myomectomy during pregnancy: A systematic review This is not something done casually. It is reserved for situations where the fibroid is causing genuine harm and nothing else is working.
Having Fibroids Removed Before Pregnancy
If fibroids are discovered before you conceive and are likely to cause problems, removing them ahead of time (pre-pregnancy myomectomy) is an option. This is especially worth considering for submucosal fibroids, which have the clearest link to fertility problems and pregnancy loss. The surgery does, however, introduce its own set of considerations for future pregnancies.
The main concern is uterine rupture, where the scar from the myomectomy gives way during a subsequent pregnancy or labor. A systematic review estimated the risk of uterine rupture during a trial of labor after myomectomy at about 0.47%.23PubMed. Trial of labor after myomectomy and uterine rupture: a systematic review A single-center study of laparoscopic myomectomy found a similar rate of about 0.6%, and about three-quarters of subsequent pregnancies reached full term.24PubMed. Pregnancy Outcomes and Risk Factors for Uterine Rupture After Laparoscopic Myomectomy In a multicenter case series examining uterine rupture after myomectomy, none of the 14 ruptures occurred during labor itself, suggesting that most ruptures happen earlier in pregnancy and may relate to the scar’s integrity rather than the mechanical forces of active labor.25PubMed Central. Uterine rupture in pregnancies following myomectomy: A multicenter case series
Many providers recommend waiting about 12 to 18 months after myomectomy before attempting pregnancy, to allow the uterine scar to heal fully. The average interval between surgery and conception in published series is around 14 months.26PubMed. Pregnancy Outcomes and Risk Factors for Uterine Rupture After Laparoscopic Myomectomy Whether you can attempt vaginal delivery or need a planned cesarean after myomectomy depends on factors like the depth and location of the scar and your surgeon’s assessment.
Uterine Artery Embolization and Future Fertility
Uterine artery embolization (UAE) is a minimally invasive procedure that shrinks fibroids by cutting off their blood supply. It is effective for symptom relief, but its role for people who want future pregnancies is more contentious. A systematic review and meta-analysis found that among women who wished to become pregnant after UAE, about 40% achieved at least one pregnancy. However, the pregnancy loss rate was about a third, with most losses due to spontaneous miscarriage.27PubMed. Pregnancy and its Outcomes in Patients After Uterine Fibroid Embolization: A Systematic Review and Meta-Analysis
A smaller single-center study reported more optimistic numbers, with about 88% of post-UAE pregnancies resulting in live births, though all deliveries were by cesarean section and two cases of placenta accreta (where the placenta grows too deeply into the uterine wall) were observed.28PubMed Central. Pregnancy after uterine arterial embolization Placenta accreta is a serious complication, and the association with prior UAE, even in small numbers, is something providers take seriously. Most guidelines still recommend myomectomy over UAE for people whose primary concern is preserving fertility, though UAE is not absolutely off the table if myomectomy is not a good option for other reasons.
Fibroids and IVF
For people pursuing in vitro fertilization, intramural fibroids add a layer of complexity. A study of frozen-thawed euploid blastocyst transfers (where embryos are genetically screened before implantation) found that larger fibroid diameter was an independent predictor of early miscarriage.29PubMed Central. Influencing factors for early miscarriage after frozen-thawed euploid blastocyst transfer in patients with intramural uterine fibroids This is notable because euploid embryos have normal chromosomes, so the miscarriage is more likely caused by the uterine environment than by genetic problems with the embryo. It reinforces the idea that fibroid size matters: even when you control for embryo quality, a larger intramural fibroid makes it harder for the pregnancy to stick.
Fertility specialists generally consider fibroid removal before IVF if the fibroids are submucosal or if intramural fibroids are large enough to distort the uterine cavity. The exact size cutoff is debated, but many clinicians become more concerned once intramural fibroids exceed about four to five centimeters. This threshold is not absolute, and factors like how close the fibroid is to the cavity lining also play a role.
Emotional and Quality-of-Life Effects
The physical complications get most of the attention, but the psychological burden of carrying fibroids through pregnancy is real. A cross-sectional study in China found that pregnant women with fibroids scored lower on standardized quality-of-life measures than those without, with particular struggles around self-care and performing usual daily activities.30PubMed Central. Health-related quality of life in pregnancy with uterine fibroid: a cross-sectional study in China The anxiety of knowing fibroids could complicate things, combined with potential pain episodes and more frequent monitoring visits, adds up. If you are dealing with this, it is worth raising with your provider. More frequent reassurance scans, a clear pain-management plan, and honest conversations about what to expect can make a meaningful difference in how the pregnancy feels day to day.
The Genetics Behind Fibroid Development
Fibroids grow from smooth muscle cells in the uterine wall, and their development is driven by specific genetic mutations. The most common mutations affect a gene called MED12, found in roughly three-quarters of fibroids, and the HMGA2 gene, found in about 10%. MED12 mutations are linked to increased genomic instability and greater sensitivity to progesterone, which is one reason fibroids tend to grow during the progesterone-rich environment of pregnancy.31PubMed Central. Uterine Fibroids This genetic basis also helps explain why fibroids are so common and why they run in families: if your mother or sister had fibroids, your own risk is substantially higher. Understanding the molecular drivers has not yet translated into targeted prevention, but it is an active area of research that may eventually lead to treatments that prevent fibroids from forming in the first place rather than managing them once they appear.