In adenomyosis, endometrial-like tissue grows into the muscular wall of the womb. In endometriosis, similar tissue grows outside the womb. Symptoms overlap, and many women have both.
Adenomyosis and endometriosis are often mentioned in the same breath, and for good reason. Both involve endometrial-type tissue growing where it does not belong, both can cause heavy and painful periods, and both are frequently missed for years before anyone gives them a name. They are, however, two separate conditions. They sit in different places in the body, they are confirmed in different ways, and the treatment conversations that follow are not identical.
If you have been told you might have one or the other, or you have spent months searching for an explanation for pain and bloating that nobody has taken seriously, this guide sets out what actually separates them. It covers the anatomy in plain language, the symptoms they share and the ones that point towards a particular diagnosis, the swollen lower abdomen that many women call an adenomyosis belly, how each condition is diagnosed, what each means for fertility, and the treatment routes that exist for both.
What Are Adenomyosis and Endometriosis?
Adenomyosis in plain language
The womb has three layers. The innermost lining, the endometrium, is the layer that thickens each month and is shed as a period. Around it sits a thick band of muscle called the myometrium, and outside that a thin outer covering. In adenomyosis, endometrial-type tissue is found growing down inside the muscular wall itself. That tissue still responds to the hormones of your cycle, so each month it swells and bleeds inside the muscle, where the blood has nowhere to drain.
The result is a womb that becomes boggy, tender and often noticeably enlarged. It can be diffuse, meaning the tissue is scattered throughout the muscle wall, or focal, forming a discrete area sometimes described as an adenomyoma. Either way, the problem is contained within the organ itself.
Endometriosis in plain language
In endometriosis, similar tissue is found outside the womb altogether. The most common sites are the ovaries, the ligaments that support the womb, the lining of the pelvis, the space behind the womb, the bowel and the bladder. In rarer cases deposits are found further afield, including on the diaphragm.
These deposits also respond to hormonal signals, bleeding and inflaming the surrounding tissue month after month. Over time this repeated irritation can create scar tissue and adhesions, sticky bands that bind pelvic organs to one another. On the ovaries, endometriosis can form fluid-filled cysts known as endometriomas. If you would like a fuller description of the sensation itself, our article on what endometriosis actually feels like goes into more detail.
The Key Difference: Inside the Muscle or Outside the Womb
If you remember only one thing, make it this. Adenomyosis grows into the muscular wall of the uterus. Endometriosis grows outside the uterus, in the pelvis and occasionally beyond it. Same type of tissue, entirely different address.
That single distinction explains almost everything else about the two conditions. Because adenomyosis is trapped inside the muscle, its effect is on the womb itself: the organ enlarges, its ability to contract in a coordinated way is disturbed, and the lining bleeds more heavily. Heavy flow and deep, dragging cramps are the natural consequence.
Because endometriosis sits on and between other structures, its effect is on the pelvis as a whole. Pain follows wherever the deposits are, which is why one woman describes pain during sex, another pain when opening her bowels, and a third a stabbing pain on one side that has nothing to do with her period. Adhesions can pull organs out of position, and the ovaries and fallopian tubes can be caught up in the process.
This also explains why the two are diagnosed differently. A condition inside the womb wall shows up on imaging of the womb. A condition scattered across the pelvic lining often does not show up at all until someone looks inside.
Symptoms: Where They Overlap and Where They Differ
The overlap is genuinely large, which is why the two are so often confused. Both cause painful periods, and in both cases the pain tends to be worse than the discomfort most women accept as normal. Both are associated with chronic pelvic pain between periods, with fatigue, and with pain during or after sex. Both can leave you exhausted and low, partly from the pain and partly from the blood loss.
Certain patterns, however, lean one way rather than the other. Very heavy bleeding, flooding, passing large clots and a period that seems to get heavier year on year point more strongly towards adenomyosis. So does a cramping pain that feels deep, central and pressing, sometimes described as a heavy weight low in the pelvis, and a womb that feels tender when pressed during an examination.
Endometriosis more often produces pain that is not confined to the womb. Pain that begins a day or two before bleeding starts, pain deep inside during intercourse, pain on passing stool or urine during a period, cyclical bowel disturbance, and one-sided pelvic pain all suggest deposits outside the uterus. Endometriosis is also more likely to be linked with difficulty conceiving as the presenting problem, sometimes discovered when a woman is investigated for infertility rather than for pain.
None of this is diagnostic on its own. Plenty of women with adenomyosis have modest bleeding, and plenty with endometriosis have textbook heavy periods. The pattern simply gives your doctor a starting point. Because so many pelvic conditions share these features, it is worth reading more broadly about the possible causes of pelvic pain in women before assuming any single diagnosis.
What Is "Adenomyosis Belly"?
Adenomyosis belly is not a medical term, but it describes something real that a great many women experience. It refers to a lower abdomen that looks and feels swollen, firm and distended, often to the point where clothes that fitted in the morning are uncomfortable by the evening. Women frequently describe looking several months pregnant, and the swelling tends to worsen in the days before and during a period.
Two separate processes contribute. The first is the womb itself. In adenomyosis the uterus is genuinely enlarged, sometimes to the size it would reach in early pregnancy, and a large uterus sitting low in the pelvis pushes the abdominal wall forward. This part of the swelling is structural and does not disappear with diet.
The second is bloating in the ordinary sense: gas, fluid retention and slowed bowel transit. Inflammation in the pelvis, the hormonal shifts of the luteal phase and the effect of prostaglandins on the gut all play a part. This is why the distension fluctuates through the day and through the cycle, and why it often eases once bleeding is established.
Endometriosis produces a similar swelling, commonly called endo belly, through the second mechanism rather than the first. So bloating alone does not tell you which condition you have. What can be informative is whether the swelling ever fully settles. A lower abdomen that is somewhat firm even in the middle of your cycle raises the possibility of an enlarged womb, which is worth mentioning to your doctor. Fibroids can create exactly the same appearance, so the symptom overlaps with fibroid symptoms as well.
Who Gets Each Condition?
The typical profiles differ, although there is a great deal of crossover and neither picture is a rule.
Adenomyosis has classically been described in women in their late thirties and forties who have had at least one child, and particularly in those who have had a caesarean section, a surgical procedure on the womb or a previous termination. The theory is that any breach of the boundary between the lining and the muscle may allow endometrial tissue to become embedded. Higher lifetime oestrogen exposure is also thought to contribute. Newer imaging has, however, shown adenomyosis in younger women and in women who have never been pregnant, so the older assumption that it is purely a condition of later reproductive life is being revised.
Endometriosis usually announces itself earlier. Symptoms often begin in the teens or twenties, sometimes with the very first periods, and childbirth history is not part of the picture. There is a clear familial tendency: having a mother or sister with endometriosis raises your own likelihood. Early first periods, short cycles, long or heavy bleeding and never having been pregnant are all associated with it.
One shared frustration is the delay. Both conditions are commonly dismissed as normal period pain for years, and both are more likely to be recognised when a woman describes her symptoms in specific terms rather than simply saying her periods are bad.
How Each Condition Is Diagnosed
This is where the two diverge most sharply, and it is worth understanding before an appointment.
Adenomyosis can often be identified without surgery. A transvaginal ultrasound performed by someone specifically looking for it may show a globally enlarged womb, an asymmetrically thickened muscle wall, small cysts within the muscle, an indistinct border between the lining and the muscle, and a characteristic streaky or fan-shaped shadowing. MRI is more detailed and is particularly useful for measuring the junctional zone, the innermost band of the muscle wall, which is typically thickened in adenomyosis. A confident working diagnosis is therefore usually reachable through imaging alone. Absolute confirmation traditionally came only from examining the womb after hysterectomy, which is precisely why imaging expertise matters so much.
Endometriosis is the opposite. Ultrasound reliably shows endometriomas on the ovaries and can suggest deep deposits in experienced hands, but superficial peritoneal disease, which is the most common form, is frequently invisible on any scan. A normal ultrasound does not rule endometriosis out, and this single fact accounts for an enormous amount of misplaced reassurance. Definitive diagnosis is made at laparoscopic surgery, when a camera is passed into the abdomen through a small incision so that the pelvis can be inspected directly and tissue taken for examination.
So the practical difference is this: adenomyosis is often confirmed by a scan, whereas endometriosis frequently requires a look inside. Many specialists will nonetheless begin treatment for suspected endometriosis based on symptoms alone, rather than sending every woman straight to theatre.
Can You Have Both at the Same Time?
Yes, and it is far more common than most women realise. A substantial proportion of those diagnosed with one condition are found to have the other as well, particularly women who have both severe pain and very heavy bleeding.
This matters practically. If you have had endometriosis treated surgically and your pain improved but your periods remained heavy and dragging, undiagnosed adenomyosis may be the reason. Equally, if adenomyosis has been identified on a scan but you also have pain with bowel movements, one-sided pain or deep pain during sex, coexisting endometriosis is worth raising.
The two conditions are also frequently accompanied by fibroids, which adds another layer. Because their symptoms blur into one another, treatment plans in these situations are usually built around the symptom that is affecting you most, rather than around a single label. If your periods have also become irregular or unpredictable alongside the pain, that is worth mentioning as well, since it may point to an additional factor that needs investigating in parallel.
Fertility and Pregnancy With Each Condition
Both conditions can make conceiving harder, but they interfere at different points.
Endometriosis can affect fertility mechanically and biochemically. Adhesions may distort the relationship between the ovary and the fallopian tube so that the egg is not picked up efficiently, tubes may become blocked, and endometriomas can reduce the pool of eggs within the ovary. Inflammatory changes in the pelvic fluid may also affect sperm function and early embryo development. The extent of the effect varies enormously, and many women with endometriosis conceive without any assistance. Our guide to getting pregnant with endometriosis covers the options in more depth.
Adenomyosis interferes closer to home. A womb whose muscle wall is infiltrated and inflamed may contract abnormally, and the environment of the lining itself may be less receptive to an embryo attempting to implant. There is also an association with certain complications later in pregnancy, which is one reason why women with known adenomyosis are often followed a little more closely once pregnant.
Neither diagnosis means pregnancy is out of reach. What both mean is that if you have been trying for a year without success, or six months if you are over thirty-five, it is reasonable to ask for investigation earlier rather than later, because time matters and the conditions themselves can progress.
Treatment Options Compared
Treatment for both conditions falls into the same broad categories, but the emphasis differs.
For pain relief, anti-inflammatory painkillers taken regularly from just before bleeding begins, rather than once pain is established, are usually the first step in both conditions. They work by reducing the prostaglandins that drive cramping, and taking them early makes a noticeable difference to how well they work.
Hormonal treatment is the mainstay of medical management for both. The principle is to reduce or flatten the hormonal cycling that feeds the abnormal tissue. Options include combined hormonal contraception taken continuously or with fewer breaks, progestogen-only preparations, and a hormone-releasing intrauterine device, which delivers progestogen directly to the lining and is particularly relevant in adenomyosis because it addresses both the pain and the heavy bleeding. Medicines that temporarily suppress ovarian function altogether are sometimes used for a limited period under specialist supervision. Non-hormonal medication to reduce menstrual blood loss can be added when bleeding is the dominant problem.
Surgery is where the two differ most. In endometriosis, the aim is to remove or destroy the deposits and divide adhesions while preserving the organs, which is done laparoscopically and is the same operation that establishes the diagnosis. In adenomyosis, the disease is inside the muscle and cannot be neatly excised in most cases. Focal adenomyomas can sometimes be removed, and there are uterus-preserving techniques, but the only treatment that definitively ends adenomyosis is hysterectomy.
Hysterectomy is a significant decision and is generally reserved for women with severe symptoms who have completed their families and for whom other approaches have not given adequate relief. It is a conversation to have unhurriedly, with a clear understanding of what is and is not removed, because taking the womb does not treat endometriosis deposits elsewhere in the pelvis if those are also present.
Day-to-Day Pain Management and What to Track
Between appointments, the practical measures that help are broadly the same for both conditions. Heat applied to the lower abdomen or back relaxes the muscle and is genuinely effective for cramping. Gentle regular movement, including walking, swimming and stretching, tends to help more than complete rest, although it can feel counterintuitive on the worst days. Attention to sleep, and to the stress that amplifies pain perception, is not a soft extra but part of the management. If bleeding is heavy, ask whether your iron levels have been checked, because anaemia turns manageable fatigue into exhaustion.
What you bring to your appointment shapes what happens in it. Vague descriptions of bad periods invite vague responses. Specific records invite investigation. For three cycles, if you can, keep a note of the following:
- The first and last day of bleeding, and which days were heaviest
- How often you needed to change protection on your heaviest day, and whether you passed clots or flooded through onto clothing or bedding
- Pain scored out of ten each day, with a note of what you took and whether it helped
- Whether pain occurred with sex, with opening your bowels or with passing urine, and whether it was cyclical
- Days when your abdomen was visibly swollen, and whether it settled overnight
- Days missed from work, study or normal activity
Take this record with you, along with any previous scan reports. If you have been dismissed before, saying plainly that the pain stops you functioning, and that you would like to know whether adenomyosis or endometriosis has been considered, is a reasonable and useful thing to do.
When to See a Doctor
Period pain that responds to simple painkillers and does not interfere with your life is common and usually needs no investigation. Beyond that, there is no benefit in waiting.
Arrange an appointment if your periods are so painful that you regularly miss work, school or normal activities, if pain is not controlled by over-the-counter medication, if bleeding is heavy enough that you soak through protection in an hour or pass clots larger than a coin, if you bleed between periods, if sex is painful, if your lower abdomen is persistently swollen, or if you have been trying to conceive for a year without success.
Seek urgent medical attention for sudden severe pelvic pain that comes on out of the blue, especially with faintness, fever or vomiting, since this can indicate a cyst complication or another acute problem. Very heavy bleeding accompanied by dizziness, breathlessness or a racing heart also needs same-day assessment.
Adenomyosis and endometriosis are both long-term conditions, and neither has a single quick fix. What they do have is a range of approaches that can substantially change how you feel, and the first step in all of them is getting the right name attached to your symptoms.
References
This article was prepared with reference to the following independent health sources.
- NHS. Adenomyosis
- NHS. Endometriosis
