Fibroids can reduce your chances of getting pregnant, but the impact depends almost entirely on where they grow and how much they change the shape of your uterine cavity. Submucosal fibroids, which grow into the cavity where a pregnancy implants, have the clearest negative effect on fertility. Fibroids growing on the outer surface of the uterus generally don’t affect fertility at all. The ones in between, intramural fibroids sitting within the uterine wall, fall into a gray area that depends on their size and proximity to the lining.
Location Matters More Than Size
The uterus has three layers, and fibroids can grow in any of them. Where a fibroid sits relative to the uterine cavity is the single biggest factor in whether it will interfere with conception or pregnancy. Fibroids are classified by type on a scale from 0 to 8 based on their position, and that number tells fertility specialists far more than the fibroid’s size alone.
Submucosal fibroids (types 0, 1, and 2) grow partially or fully inside the uterine cavity. These have the most consistent negative impact on fertility. They physically distort the space where an embryo needs to implant and can alter the lining tissue itself. Removing them improves pregnancy rates, and this is one of the few points in fibroid-fertility research where there’s strong consensus.
Subserosal fibroids grow on the outside of the uterus, projecting into the abdominal cavity. These don’t appear to impair fertility, and removing them in women without symptoms offers no reproductive benefit.
Intramural fibroids, embedded in the muscular wall, are the most debated. A large meta-analysis of 15 studies found that women with intramural fibroids that don’t distort the cavity still had 32% lower odds of clinical pregnancy during IVF compared to women without fibroids. That’s a meaningful reduction even when the cavity looks normal on imaging. One explanation is that fibroids touching or pressing close to the inner lining (classified as type 3) may cause subtle damage that doesn’t show up as obvious distortion. Women with type 3 fibroids 30 mm or larger showed implantation rates of just 15.7% compared to 38.1% in women without fibroids, and live birth rates dropped to 16.5% versus 30.4%.
The American Society for Reproductive Medicine notes that intramural fibroids larger than about 6 cm (roughly the size of a lime) are commonly associated with decreased fertility, even if they don’t visibly push into the cavity.
How Fibroids Disrupt the Uterine Environment
Fibroids don’t just block space. They change the biology of the uterus in several ways that make it harder for an embryo to implant and a pregnancy to sustain itself.
One of the most significant effects is on blood flow. Fibroids produce excessive structural tissue that compresses surrounding blood vessels, reducing the blood supply reaching the endometrium, the lining where an embryo implants. At the same time, fibroids drive overproduction of blood vessel growth factors, creating a chaotic vascular environment with dilated veins and abnormal constriction patterns. The result is a lining that may look thick enough on ultrasound but doesn’t function normally at the molecular level.
Fibroids also increase uterine contractility. The muscular wall of the uterus needs to be relatively calm during the implantation window, and fibroids can cause abnormal contractions that physically interfere with an embryo settling into the lining. This may partly explain why even fibroids that don’t distort the cavity still reduce pregnancy rates.
At the cellular level, fibroids reduce the production of key signaling molecules that the lining needs to accept an embryo. They also suppress expression of a gene called HOXA-10, which plays a direct role in making the endometrium receptive during the window when implantation is possible. Additionally, fibroids near the openings of the fallopian tubes can physically block sperm or embryo transport, though this is less common than the implantation-related effects.
Heavy Bleeding and Its Ripple Effects
Many women with fibroids experience heavy or prolonged menstrual bleeding, which is itself linked to the vascular disruption fibroids cause. Women with fibroids tend to have more dilated blood vessels in the endometrial lining compared to women without them, and the abnormal vessel constriction patterns mean bleeding doesn’t stop as efficiently at the end of a period.
Chronic heavy bleeding can lead to iron-deficiency anemia, which affects energy and overall health but can also compromise the quality of the uterine environment. Beyond the direct biological effects, heavy and unpredictable cycles can make timing conception more difficult and may signal that the endometrium is cycling abnormally.
When Removal Improves Fertility
Surgical removal of fibroids (myomectomy) clearly benefits fertility in one scenario: when fibroids distort the uterine cavity. For submucosal fibroids, hysteroscopic removal, a procedure done through the cervix with no abdominal incisions, is typically straightforward and is associated with improved pregnancy rates afterward.
For intramural fibroids with a submucosal component, meaning they push into the cavity even partially, myomectomy may also be considered to improve pregnancy outcomes. This can be done laparoscopically or through an open incision depending on the size and number of fibroids.
The picture is far less clear for fibroids that don’t distort the cavity. The American Society for Reproductive Medicine advises against myomectomy to improve pregnancy outcomes in women with non-cavity-distorting fibroids who have no symptoms. The evidence simply isn’t strong enough to show that the benefits of surgery outweigh the risks, which include scarring, adhesion formation, and in rare cases, uterine rupture during a future pregnancy. There’s no confirmed threshold for size, number, or specific wall location (outside of cavity distortion) that reliably predicts who will benefit from removal.
This creates a frustrating situation for women with intramural fibroids and unexplained infertility. The data shows these fibroids do reduce pregnancy odds on a population level, but there’s no clear guideline for when removing them actually helps an individual patient. Decisions in this gray zone typically involve weighing the fibroid’s size, how close it sits to the lining, how long you’ve been trying to conceive, your age, and whether you’re pursuing IVF.
Fibroids and Pregnancy Complications
Even after conception, fibroids can affect how a pregnancy progresses. Fibroids that distort the cavity are associated with a higher risk of early pregnancy loss, likely through the same mechanisms that impair implantation: poor blood supply to the area where the placenta attaches, abnormal uterine contractions, and an inflammatory local environment.
Later in pregnancy, larger fibroids can contribute to preterm labor, placental abruption (where the placenta separates from the uterine wall prematurely), and malpresentation (when the baby doesn’t settle into a head-down position because the fibroid occupies space). Fibroids can also grow during pregnancy due to increased estrogen and blood flow, sometimes causing pain if they outgrow their blood supply, a process called degeneration.
Not every fibroid causes problems during pregnancy. Many women with small or favorably positioned fibroids carry pregnancies to term without complications. The risk increases with fibroids that are large, multiple, or located near the placental implantation site.
What This Means If You’re Trying to Conceive
If you’ve been diagnosed with fibroids and are trying to get pregnant, the most important thing to establish is exactly where your fibroids are and whether they change the shape of your uterine cavity. A saline infusion sonogram or an MRI can give a much clearer picture than a standard ultrasound alone. Submucosal fibroids that distort the cavity are the strongest candidates for removal before conception, and the procedure for small ones is relatively minor. For intramural fibroids that don’t touch the cavity, the decision is more nuanced and depends on your full clinical picture.
If you’re pursuing IVF, fibroid location becomes even more relevant because the data on reduced implantation and live birth rates comes largely from IVF populations where outcomes are tracked precisely. A type 3 intramural fibroid that might not matter for natural conception could meaningfully reduce your chances per IVF cycle, especially if it’s 3 cm or larger.