Adenomyosis and uterine fibroids are two of the most common structural conditions affecting the uterus. Both can cause heavy periods and pelvic pain, and both are frequently identified during a fertility evaluation.
They are, however, distinct conditions with different effects on conception. Understanding the difference matters because the treatment approach and the implications for implantation are not the same.
What Adenomyosis Is
Adenomyosis occurs when tissue similar to the uterine lining grows into the muscular wall of the uterus. The affected muscle becomes thickened and inflamed, and the uterus is often diffusely enlarged.
The condition is most commonly diagnosed in women in their thirties and forties, though it is increasingly identified in younger women as imaging quality improves. Typical features include heavy menstrual bleeding, progressively worsening period pain, and a sensation of pelvic heaviness. A proportion of women have no symptoms at all and are diagnosed incidentally.
What Uterine Fibroids Are
Fibroids, also called leiomyomas, are benign growths arising from the smooth muscle of the uterus. Unlike adenomyosis, which is diffuse, fibroids are discrete masses with defined borders, and a woman may have one or several.
Their classification depends on location, which is the single most important factor in assessing their effect on fertility.
- Submucosal fibroids: These project into the uterine cavity and have the greatest effect on implantation.
- Intramural fibroids: These sit within the muscular wall. Their effect depends on size and on whether they distort the cavity.
- Subserosal fibroids: These grow outward from the outer surface of the uterus and generally have little effect on fertility.
Adenomyosis vs Fibroids
| Adenomyosis | Fibroids | |
| Nature of the condition | Diffuse infiltration of the uterine wall | Discrete, well-defined benign tumors |
| Tissue of origin | Tissue similar to the uterine lining | Smooth muscle of the uterus |
| Borders on imaging | Poorly defined | Clearly defined |
| Effect on uterine shape | Uniform enlargement, often asymmetrical thickening | Localized bulges depending on position |
| Typical age at diagnosis | Thirties and forties | Reproductive years onward |
| Principal symptom | Heavy bleeding with progressive period pain | Heavy bleeding, pressure symptoms, pain in some cases |
| Preferred imaging | MRI, or transvaginal ultrasound by an experienced operator | Transvaginal ultrasound |
| Surgical removal | Difficult, as the tissue has no clear plane | Feasible, as the fibroid can be shelled out |
Difference Between Fibroids and Adenomyosis in Clinical Terms
The practical difference between fibroids and adenomyosis lies in whether the abnormality can be removed.
A fibroid is a defined mass with a surrounding plane, which means a surgeon can separate it from healthy muscle and remove it while preserving the uterus. Adenomyosis has no such plane. The abnormal tissue is interwoven with normal muscle, so complete removal without compromising the uterus is generally not possible. Management therefore focuses on medical suppression and on optimizing the uterine environment before embryo transfer rather than on excision.
The two conditions also coexist frequently. A woman diagnosed with fibroids may have adenomyosis as well, which is one reason a scan reported as showing fibroids alone does not always account for the full clinical picture.
Adenomyosis and Implantation Failure
The relationship between adenomyosis and implantation failure operates through several mechanisms.
- Altered uterine contractility: The junctional zone, the inner layer of muscle immediately beneath the lining, is typically thickened in adenomyosis. Abnormal contraction patterns in this zone may interfere with the transport and settling of an embryo.
- Inflammatory changes in the lining: The endometrium in adenomyosis shows raised levels of inflammatory mediators, which may reduce receptivity at the point of implantation.
- Altered progesterone response: Research indicates that the lining may respond differently to progesterone, which is central to preparing the endometrium for an embryo.
- Impaired blood supply: Changes in the vascular pattern of the affected wall may compromise the environment required for early placental development.
These changes explain why some women with adenomyosis produce good quality embryos that repeatedly do not implant. Where implantation failure recurs, and standard investigations are normal, adenomyosis is one of the conditions that warrants specific assessment.
Uterine Fibroids and Pregnancy Chances
The effect of uterine fibroids and pregnancy chances depends almost entirely on position rather than on the presence of fibroids as such.
Submucosal fibroids, which distort the uterine cavity, are consistently associated with reduced implantation and pregnancy rates, and their removal is generally recommended before fertility treatment. The evidence supporting improved outcomes after removal is strongest for this group.
Intramural fibroids present a more nuanced picture. Those that do not distort the cavity may have a limited effect, particularly when small. Larger intramural fibroids, and those that press on the cavity, are more likely to be clinically significant, and the decision to operate depends on factors such as size, number, position, the patient’s age, and the duration of infertility.
Subserosal fibroids rarely affect implantation and are usually managed only where they cause pressure symptoms.
Does Adenomyosis Affect IVF Success?
How adenomyosis affects IVF success is a common concern, but the full picture comes down to two key factors:
What research shows: Women with adenomyosis generally face lower pregnancy rates and a higher risk of miscarriage compared to those without the condition. However, because clinics diagnose and measure severity differently, results vary from person to person.
Egg quality remains strong: Adenomyosis affects the uterus, not the eggs. This means you can still produce healthy, high-quality embryos; the main challenge is helping them implant successfully.
Preparation makes a big difference: Treatment before embryo transfer can significantly improve your chances. Doctors often use a period of hormone therapy (such as GnRH agonists) to calm the uterine environment before doing a frozen embryo transfer. Your specialist will customize this plan based on your age, egg reserve, and the extent of the condition.
How Each Condition Is Diagnosed
Neither condition is diagnosed on symptoms alone, since heavy bleeding and pelvic pain are common to both.
Transvaginal ultrasound: The first-line investigation for both conditions. It identifies fibroids reliably and, when performed by an operator experienced in the features of adenomyosis, detects the condition with reasonable accuracy.
MRI: Provides the clearest assessment of adenomyosis, particularly where the diagnosis is uncertain or where the two conditions coexist and need to be distinguished.
Hysteroscopy: Allows direct visualization of the uterine cavity and is used to assess submucosal fibroids and cavity distortion. Removal can frequently be carried out during the same procedure.
Saline infusion sonography: Improves assessment of the cavity outline and is helpful in determining whether a fibroid encroaches on it.
Conclusion
Adenomyosis and fibroids are often discussed together because their symptoms overlap, but they behave differently and require different management. Fibroids are discrete and, where they distort the cavity, removable, with a clear benefit to implantation. Adenomyosis is diffuse, is not usually amenable to surgery, and is managed by preparing the uterine environment before transfer.
Both are compatible with pregnancy, including through IVF. What determines the outcome is accurate identification of which condition is present, where it sits, and what preparation the uterus requires before an embryo transfer is attempted.
Consult a Fertility Specialist at 9M Fertility
If you are experiencing heavy periods, repeated implantation failure, or have questions about a recent pelvic scan, a detailed evaluation can help provide clarity.
The specialists at 9M Fertility offer thorough assessments to help identify underlying factors affecting your reproductive health and guide you toward appropriate next steps tailored to your timeline.
Book a consultation with 9M Fertility for a complete fertility evaluation. Contact Us
