Most fibroids coexist with pregnancy without causing serious harm, but they do raise the odds of several complications depending on their size, number, and location in the uterus. A large meta-analysis found that after adjusting for other risk factors, fibroids were linked to higher rates of preterm birth, cesarean delivery, placenta previa, placental abruption, postpartum hemorrhage, breech presentation, preeclampsia, and intrauterine fetal death.1PubMed Central. The influence of uterine fibroids on adverse outcomes in pregnant women: a meta-analysis That sounds alarming as a list, but the absolute risk of each complication remains relatively low for any individual pregnancy, and many people with fibroids deliver healthy babies without incident. The picture is more nuanced than a simple “safe” or “dangerous” label.
How Fibroids Behave During Pregnancy
Fibroids often grow during the first trimester, sometimes rapidly. The conventional explanation blamed estrogen and progesterone, which rise steadily throughout pregnancy. But those hormones climb gradually, while fibroids tend to balloon early and then plateau or even shrink later on. Research has pointed to hCG, the hormone that spikes in the first weeks of pregnancy, as a better explanation. One study found a strong positive correlation between rising hCG levels and increasing fibroid diameter during early pregnancy, a pattern that fits the timing much better than estrogen alone.2Fertility and Sterility. Growth trend of small uterine fibroids and human chorionic gonadotropin serum levels in early pregnancy: an observational study A separate study confirmed that fibroids grew markedly during early pregnancy when estrogen and progesterone were still low, and found no correlation between estrogen levels at the time and the degree of growth.3PLoS ONE. The Rapid Growth of Fibroids during Early Pregnancy
After the initial surge, the growth trajectory varies. Some studies found deceleration in the second half of pregnancy, others found fibroids actually shrinking in the third trimester regardless of size, and a few found no significant change at all.4PLoS ONE. The Rapid Growth of Fibroids during Early Pregnancy The takeaway is that growth is not linear or predictable, which is one reason imaging is repeated at various points during pregnancy to track what each fibroid is doing.
Do Fibroids Affect Fertility and Conception?
Where a fibroid sits in the uterus matters more than whether it exists at all. Submucosal fibroids, those that push into the uterine cavity, are consistently linked to lower pregnancy and live-birth rates and to recurrent pregnancy loss. Removing them has been shown to improve pregnancy rates.5PubMed Central. Uterine Fibroids and Infertility The mechanisms include distortion of the endometrial lining, increased uterine contractility, local inflammation, and changes in blood flow to the lining.6PubMed Central. Prognostic value of the location of submucosal uterine leiomyomas in infertility
Subserosal fibroids, which bulge outward from the uterine wall, generally do not appear to reduce fertility, and removing them before pregnancy does not seem to help.7PubMed Central. Uterine Fibroids and Infertility Intramural fibroids, embedded within the muscle wall, land in a gray zone: they do appear to reduce fertility somewhat, but whether surgery helps remains unclear, and guidelines have not reached consensus on when to remove them before attempting conception.8PubMed Central. Uterine Fibroids and Infertility
The degree to which a submucosal fibroid distorts the uterine cavity also matters. Those that extend mostly into the cavity carry a higher risk for low birth rates compared with those that are mostly embedded in the wall.9PubMed Central. Prognostic value of the location of submucosal uterine leiomyomas in infertility
Miscarriage Risk
The relationship between fibroids and miscarriage is less straightforward than many people assume. A large prospective cohort study found that the apparent link between fibroids and miscarriage disappeared once the researchers adjusted for age, race, alcohol use, and parity. In other words, women with fibroids also tended to be older and have other risk factors, and those factors explained the elevated miscarriage rate rather than the fibroids themselves.10American Journal of Epidemiology. Prospective Cohort Study of Uterine Fibroids and Miscarriage Risk
Later miscarriage, occurring in the second trimester, tells a slightly different story. A multicenter cohort study found that a single fibroid did not meaningfully raise the odds of late miscarriage, but having multiple fibroids roughly doubled the odds. Submucosal fibroids stood out: they increased the odds of late miscarriage by nearly five times, while fibroids in other locations did not reach statistical significance.11PubMed. Association of uterine fibroids with late miscarriage: multicenter cohort study So when it comes to miscarriage, what seems to matter most is having fibroids in the cavity itself or having several fibroids rather than just one.
Obstetric Complications
A comprehensive review of the pooled evidence puts specific numbers on the risks. Fibroids were associated with roughly one-and-a-half times the odds of preterm birth, about two-and-a-half times the odds of malpresentation, similar increases for placental abruption and placenta previa, about two-and-a-half times the odds of cesarean delivery, and roughly three times the odds of postpartum hemorrhage.12PubMed Central. Fibroids and pregnancy These are relative measures, not absolute ones. A threefold increase in something that has a low baseline risk still yields a fairly small absolute risk.
The size of the fibroid is a strong predictor. A cohort study of over 650 pregnancies showed that adverse events rose in a stepwise fashion with fibroid diameter: preterm birth occurred in about 12% of pregnancies with the smallest fibroids, 24% with mid-sized fibroids, and 36% with the largest. Mean birthweight also dropped with increasing fibroid size.13PubMed Central. Influence of uterine fibroid size on perinatal and neonatal outcomes: a single-centre cohort of 651 pregnancies Fibroids over 5 cm in diameter are considered more likely to grow during pregnancy and cause trouble.14PubMed Central. Arrest of labor secondary to large uterine fibroid
How Fibroids Affect the Baby
When researchers looked at birthweight and gestational age in a study that adjusted for maternal age, BMI, and race, the overall picture was reassuring: women with fibroids and women without them had similar outcomes on average.15PubMed Central. Association of uterine fibroids with birthweight and gestational age The exception was women with three or more fibroids, whose infants weighed on average about 200 grams less at birth, though gestational age was not significantly shorter.16PubMed Central. Association of uterine fibroids with birthweight and gestational age So having fibroids does not automatically mean a smaller baby, but carrying several large ones can make a difference.
Large fibroids in the lower part of the uterus can physically block the birth canal or push the baby into unusual positions. In one reported case, a lower-segment fibroid completely obstructed the canal and forced the baby into a transverse lie, requiring a cesarean.17PubMed Central. The Impact of a Huge Fibroid on Pregnancy: A Case Report In rare instances, a large lower-segment fibroid can cause deflexion of the fetal head or mild compression of the skull, which is usually identified on ultrasound and resolves after delivery.18The Journal of Maternal-Fetal Medicine. Intrapartum ultrasonographic depiction of fetal malpositioning and mild parietal bone compression in association with large lower segment uterine leiomyoma
Pain and Red Degeneration
One of the most common complications during pregnancy is fibroid-related pain, which can come on suddenly and be severe enough to mimic an emergency. The most frequent culprit is red degeneration, which happens when a fibroid outgrows its blood supply and begins to break down internally. The typical scenario is acute abdominal pain, often in the second trimester, sometimes with fever and tenderness over the fibroid. Ultrasound can usually confirm the diagnosis, and treatment is conservative: rest and pain relief. One case report describes a woman at 21 weeks who developed acute right-sided pain from red degeneration and was managed with analgesia alone, going home uneventfully within 72 hours.19BMJ Case Reports. Red degeneration of fibroid presenting with abdominal pain in pregnancy
Pain management during pregnancy requires some caution. Nonsteroidal anti-inflammatory drugs like ibuprofen should be used carefully, especially in the third trimester, where prolonged use has been associated with fetal complications including premature closure of a key blood vessel in the fetal heart, pulmonary hypertension, and low amniotic fluid levels.20PubMed Central. Contemporary Management of Fibroids in Pregnancy For that reason, acetaminophen is typically preferred, and short courses of NSAIDs may be used earlier in pregnancy under medical guidance.
When Surgery Happens During Pregnancy
Most fibroids are left alone during pregnancy. Surgery carries its own risks, and the vast majority of fibroid-related symptoms can be managed without operating. The exception is torsion, where a pedunculated (stalked) fibroid twists on itself, cutting off its blood supply. This is a true emergency. One case involved three large subserosal fibroids, the largest 15 cm in diameter, where the stalk had twisted and the tissue was already dying; the patient needed an open myomectomy at 18 weeks.21PubMed Central. Uterine Fibroid Torsion during Pregnancy: A Case of Laparotomic Myomectomy at 18 Weeks’ Gestation with Systematic Review of the Literature
In the first trimester, laparoscopic removal of a torsed fibroid has been performed successfully. Reports describe safe application of minimally invasive surgery to remove a twisted fibroid with a normal pregnancy continuing afterward.22PubMed Central. Laparoscopic approach to fibroid torsion presenting as an acute abdomen in pregnancy The choice between laparoscopy and open surgery depends on how far along the pregnancy is, the size and location of the fibroid, and what surgical expertise is available.23PubMed Central. Laparoscopic Excision of a Pedunculated Uterine Leiomyoma in Torsion as a Cause of Acute Abdomen at 10 Weeks of Pregnancy These cases are rare, but recognizing torsion quickly is important because delay can lead to necrosis and serious complications.
Myomectomy Before Pregnancy
For people whose fibroids are affecting fertility, surgical removal (myomectomy) before trying to conceive is a common strategy. In a retrospective study of 180 women who underwent myomectomy, about half became pregnant afterward. Age was a major factor: women over 35 had substantially lower odds of conceiving after surgery compared with younger women. Having no prior history of infertility also predicted better outcomes. The number of incisions made in the uterine wall was another important variable; more incisions meant lower pregnancy rates.24PubMed Central. Pregnancy Rate after Myomectomy and Associated Factors among Reproductive Age Women Who Had Myomectomy at Saint Paul’s Hospital Millennium Medical College, Addis Ababa
A key concern with myomectomy is uterine rupture during a subsequent pregnancy. A systematic review found the overall rate to be about 0.5% of pregnancies after myomectomy, comparable to the rate of uterine rupture after a prior cesarean delivery.25Reproductive BioMedicine Online. Time interval from myomectomy to pregnancy and occurrence of uterine rupture: a systematic review Whether the surgery was done laparoscopically or through an open incision appears to matter: a large review of over 54,000 myomectomies found an overall rupture rate of about 0.4%, but the rate was higher after laparoscopic surgery than after open surgery.26PubMed. Risk of uterine rupture after myomectomy by laparoscopy or laparotomy This likely reflects how the uterine wall is repaired; layered suturing, which is easier during open surgery, may produce a stronger scar.
One reassuring finding is that waiting longer between myomectomy and conception did not appear to reduce the risk of rupture, which means there may not be a mandatory waiting period.27Reproductive BioMedicine Online. Time interval from myomectomy to pregnancy and occurrence of uterine rupture: a systematic review In a case series of 14 uterine ruptures after myomectomy, none occurred during labor itself; they happened before labor, which changes the risk calculus around vaginal delivery after myomectomy. All mothers survived despite significant hemorrhage in some cases.28PubMed Central. Uterine rupture in pregnancies following myomectomy: A multicenter case series A larger single-center review reported about 77% full-term deliveries and 19% vaginal deliveries after laparoscopic myomectomy, with only three uterine ruptures among 523 pregnancies.29PubMed. Pregnancy Outcomes and Risk Factors for Uterine Rupture After Laparoscopic Myomectomy: A Single-Center Experience and Literature Review
Uterine Artery Embolization and Future Pregnancy
Uterine artery embolization (UAE) is a less invasive alternative to myomectomy that cuts off blood flow to fibroids, causing them to shrink. It is generally not recommended as a first-line treatment for people planning pregnancy, but some women do conceive afterward. A Brazilian study of 15 spontaneous pregnancies following UAE found a live-birth rate of nearly 88%, with most deliveries occurring between 36 and 39 weeks. All deliveries were by cesarean. There were two cases of placenta accreta, a condition where the placenta grows too deeply into the uterine wall, which required a hysterectomy in one case.30PubMed Central. Pregnancy after uterine arterial embolization
A larger series reported 148 pregnancies and 109 live births after UAE. Whether the uterine anatomy returned to normal and whether ovarian function was preserved were the best predictors of a successful pregnancy. When the anatomy was restored, the miscarriage rate was also lower.31American Journal of Obstetrics & Gynecology. Fertility after uterine artery embolization While pregnancy after UAE is clearly possible, the elevated risk of placental problems means it is an option best discussed thoroughly with a specialist when future pregnancies are desired.
Removing Fibroids During a Cesarean
For years, surgeons were taught to leave fibroids alone during a cesarean delivery because of fear of uncontrollable bleeding. That thinking has shifted. A systematic review and meta-analysis concluded that cesarean myomectomy, removing fibroids at the same time as delivering the baby, can be safe and feasible when performed by experienced surgeons with appropriate techniques to control bleeding. The exception is fibroids located near the cornual regions of the uterus or close to large blood vessels, and cases where the uterus is not contracting well during surgery.32PubMed. Feasibility and safety of performing cesarean myomectomy: a systematic review and meta-analysis A retrospective cohort study also found no significant difference in postpartum hemorrhage, fetal distress, or neonatal outcomes when comparing cesarean myomectomy to cesarean alone.33PubMed Central. Outcomes of Myomectomy at the Time of Cesarean Section among Pregnant Women with Uterine Fibroids: A Retrospective Cohort Study This is not a routine procedure and is not appropriate for every case, but for the right patient at the right center, it offers a chance to address both the delivery and the fibroids in one operation.
What Happens to Fibroids After Delivery
Here is the part that surprises many people: fibroids tend to shrink substantially after pregnancy. Over 70% of women with live births had their fibroids shrink by more than half in volume between early pregnancy and three to six months postpartum.34PubMed Central. Postpartum factors and natural fibroid regression Even more striking, among women who had a single fibroid at the start of pregnancy, more than a third had no identifiable fibroid at all on their postpartum ultrasound, and most of the remaining ones were smaller.35PubMed Central. Pregnancy-related fibroid reduction The rapid drop in hormones after delivery, combined with the uterus returning to its normal size, appears to drive this regression. This natural shrinkage is why many clinicians advise patience: a fibroid that seemed alarming at 20 weeks may be barely detectable a few months after the baby arrives.
Imaging Challenges During Pregnancy
Diagnosing fibroids during pregnancy is not always straightforward. Ultrasound is the main tool, but a normal uterine contraction can look very similar to a fibroid on a standard scan, leading to a false diagnosis or unnecessary concern. The classic trick is simply rescanning 20 to 30 minutes later: a contraction will typically have resolved, while a fibroid stays put.36PubMed. Myoma vs. contraction in pregnancy: differentiation with color Doppler imaging Color Doppler ultrasound can also help distinguish the two: fibroids push blood vessels aside, creating a visible pattern of vessels splaying around the mass, while contractions show no vessel displacement.37Obstetrical & Gynecological Survey. Fibroids in Pregnancy—Common but Poorly Understood If your ultrasound flags a new “fibroid” that was not seen before, it is worth asking whether a repeat scan or Doppler was used to confirm.
Racial Disparities in Fibroid Burden
Any honest discussion of fibroids and pregnancy has to acknowledge that the condition does not affect everyone equally. The prevalence of fibroids is consistently higher in Black women compared to white women, and Black women tend to develop them at a younger age, have more of them, and experience more severe disease. A systematic review found that beyond biology, social and structural factors across the lifespan contribute to these disparities, including differences in environmental exposures, healthcare access, and accumulated stress. Black women with fibroids also experience worse clinical and surgical outcomes than white women with the same condition.38PubMed Central. Racial disparities in uterine fibroids and endometriosis: a systematic review and application of social, structural, and political context These disparities mean that Black women are more likely to enter pregnancy with larger or more numerous fibroids, and are disproportionately affected by the complications discussed throughout this article. Awareness of this gap matters both for patients advocating for themselves and for clinicians making management decisions.