Adenomyosis is a condition where tissue similar to the uterine lining grows into the muscular wall of the uterus. Instead of staying on the inner surface where it belongs, this tissue embeds itself deeper into the muscle, causing the uterus to enlarge and often triggering heavy, painful periods. About one in three people with adenomyosis have no symptoms at all, while others experience significant disruption to their daily lives.
What Happens Inside the Uterus
The uterus has two main layers: the endometrium (the inner lining that sheds during your period) and the myometrium (the thick muscular wall surrounding it). In adenomyosis, small islands of endometrial-like tissue push into or develop within the myometrium. These displaced pockets of tissue still respond to your monthly hormonal cycle. They thicken, break down, and attempt to bleed each month, but they’re trapped inside the muscle with nowhere to go. This causes localized swelling, inflammation, and over time can make the uterus grow two to three times its normal size.
Scientists have two main theories about why this happens. The more widely accepted one suggests that repeated cycles of tissue injury and repair at the boundary between the lining and the muscle allow endometrial cells to gradually push deeper into the wall. The alternative theory proposes that leftover embryonic cells already present in the muscle transform into endometrial-like tissue later in life. Both mechanisms may play a role, and the condition likely develops through a combination of factors rather than a single cause.
Common Symptoms
When adenomyosis does cause symptoms, the hallmark complaints are heavy menstrual bleeding and severe cramping. But the full picture can include:
- Heavy or prolonged periods that may involve passing clots or soaking through protection quickly
- Severe menstrual cramps that worsen over the years rather than staying stable
- Chronic pelvic pain that persists outside of your period
- Painful intercourse
- Bloating or abdominal fullness, sometimes called “adenomyosis belly,” caused by the enlarged uterus
- Tenderness or pressure in the lower abdomen
These symptoms often overlap with conditions like fibroids or endometriosis, which is one reason adenomyosis can go undiagnosed for years. Many people assume their painful, heavy periods are just “normal” and don’t seek evaluation until symptoms become severe.
How Adenomyosis Is Diagnosed
Adenomyosis was historically only confirmed after a hysterectomy, when a pathologist could examine the uterine tissue directly. Modern imaging has changed that. Transvaginal ultrasound is typically the first tool used, and an experienced sonographer can spot characteristic signs like an asymmetrically thickened uterine wall, a globular uterine shape, or tiny cysts within the muscle.
MRI provides an even more detailed picture. The key measurement is the thickness of the junctional zone, the transitional area between the uterine lining and the muscle. When this zone exceeds 12 millimeters on MRI, adenomyosis can be diagnosed with 85% accuracy and 96% specificity. That 12-millimeter threshold is the most widely accepted standard, though doctors also look at other features like small bright spots of trapped blood within the muscle wall.
Impact on Fertility and Pregnancy
Adenomyosis can make it harder to get pregnant and harder to stay pregnant. The displaced tissue within the uterine wall appears to interfere with embryo implantation, and the chronic inflammation may create a less hospitable environment for a developing pregnancy.
The numbers are striking. In one study comparing IVF outcomes, the overall miscarriage rate was 53% in patients with adenomyosis compared to about 20% in those without. Most of those losses occurred very early, at the biochemical stage before a pregnancy would be visible on ultrasound. The early biochemical miscarriage rate was roughly three times higher in the adenomyosis group (44% versus 15%). Clinical miscarriage rates also doubled. Women with adenomyosis who conceived through natural ovulation cycles without hormonal pretreatment had a miscarriage rate as high as 82%, compared to 12% in those without the condition.
Hormonal suppression before fertility treatment may improve these odds. In the same study, adenomyosis patients who received hormonal pretreatment before conception had a significantly lower miscarriage rate of about 36%, compared to 82% in those who didn’t. If you’re trying to conceive and have been diagnosed with adenomyosis, this is worth discussing with a reproductive specialist.
Hormonal Treatment Options
For people who want to manage symptoms without surgery, hormonal therapies are the first line of treatment. The goal is to suppress the hormonal cycles that drive the displaced tissue to swell and bleed each month.
A large network analysis of clinical trials found that one specific type of progestin (dienogest, taken as a daily pill) ranked highest for reducing adenomyosis-related pelvic pain, outperforming both the hormonal IUD and combined oral contraceptives at both three and six months. At the three-month mark, it produced significantly better pain relief than either a placebo or a hormonal IUD. By six months, it also outperformed birth control pills.
That said, the hormonal IUD remains a popular option because it delivers medication directly to the uterus and requires no daily action. Birth control pills, other progestin formulations, and medications that temporarily shut down ovarian hormone production are also used. The right choice depends on whether you’re trying to preserve fertility, your tolerance for side effects, and how severe your symptoms are.
Procedures and Surgery
When hormonal treatments don’t provide enough relief, procedural options are available.
Uterine artery embolization is a minimally invasive procedure where a specialist threads a thin catheter through a blood vessel and blocks the arteries feeding the uterus. This starves the adenomyotic tissue of its blood supply, causing it to shrink. In one study, roughly 89% of patients reported improvement in heavy bleeding, 92% had less pelvic pain, and 97% experienced relief from pressure and bulk symptoms. The procedure doesn’t require a large incision and preserves the uterus, though its effects on future fertility are not fully established.
Conservative surgery, called adenomyomectomy, involves removing the areas of adenomyosis from the uterine wall while leaving the rest of the uterus intact. This is effective at reducing both abnormal bleeding and pelvic pain, and it’s an option for people who want to keep their uterus or plan future pregnancies. However, because adenomyosis doesn’t always form a neat, contained mass the way fibroids do, complete removal can be technically challenging.
Hysterectomy, the complete removal of the uterus, remains the only definitive cure. It eliminates the possibility of recurrence entirely. This is typically considered for people who have completed childbearing and haven’t found adequate relief from other treatments.
How Adenomyosis Differs From Endometriosis
The two conditions are close relatives and frequently coexist, but they’re distinct. In endometriosis, tissue similar to the uterine lining grows outside the uterus, on organs like the ovaries, fallopian tubes, or pelvic lining. In adenomyosis, that tissue grows inward, into the uterine muscle itself. You can have one without the other, or both at the same time. The overlap in symptoms, particularly painful periods and pelvic pain, is one reason both conditions are often underdiagnosed.
Adenomyosis tends to cause a more uniformly enlarged, “boggy” uterus, while endometriosis is more associated with pain during bowel movements, urination, or ovulation depending on where the external implants are located. Treatment strategies overlap in some areas (hormonal suppression works for both), but the surgical approaches are completely different.