Adenomyosis is a condition affecting the uterus where tissue normally lining the inside starts growing into the muscular wall, causing changes that can lead to painful and heavy periods, though many women may not even realize they have it.
What is Adenomyosis?
Adenomyosis happens when the tissue that normally lines the inside of the uterus, called the endometrium, begins to grow into the muscle wall of the uterus, known as the myometrium. Think of it as the lining breaking through a barrier it should not cross. This misplaced tissue continues to behave as it normally would during a menstrual cycle. It thickens, breaks down, and bleeds with each period. However, because this tissue is trapped within the muscle wall, it has nowhere to go. This process can cause the uterus to become enlarged, sometimes doubling or even tripling in size.[1][2]
The condition is distinct from endometriosis, though the two are sometimes confused. In endometriosis, tissue similar to the uterine lining grows outside the uterus entirely, such as on the ovaries or fallopian tubes. With adenomyosis, the tissue stays within the uterus but invades the wrong layer. Some women can have both conditions at the same time, which can make diagnosis and treatment more complex.[3][7]
How Common is Adenomyosis?
Understanding how many women have adenomyosis is challenging because the condition often goes undiagnosed. Many women with adenomyosis experience no symptoms at all, meaning they may never know they have it. Estimates of how common adenomyosis is vary widely, ranging from about 5% to as high as 70% depending on the study. More recent research suggests that the true prevalence is likely between 20% and 35% of women.[4][5]
Traditionally, adenomyosis was thought to mainly affect women in their 40s and 50s who had already given birth. This belief came from the fact that the condition was usually only confirmed after a hysterectomy, a surgery to remove the uterus, which is more common in older women. However, with better imaging technology like ultrasound and MRI scans, doctors are now diagnosing adenomyosis in younger women, including those in their 30s and even teenagers. Studies show that approximately 2% to 5% of adolescents with severely painful periods have adenomyosis.[2][4]
One population-based study that followed 650,000 patients over 10 years estimated the overall incidence at 1%, or about 29 cases per 10,000 people each year. The highest rates were found in women aged 41 to 45 years. Among those diagnosed, more than 90% had symptoms that affected their daily lives.[4]
What Causes Adenomyosis?
Despite being recognized for over 150 years, the exact cause of adenomyosis remains unknown. Researchers have developed several theories to explain why the endometrial tissue starts growing into the muscle wall, but none have been definitively proven.[1][2]
The most widely accepted theory suggests that a disruption occurs in the natural boundary between the deepest layer of the endometrium and the underlying muscle. This disruption may allow endometrial cells to invade the myometrium inappropriately. Once there, the cells trigger a cycle of growth and inflammation. The misplaced endometrial tissue proliferates, small blood vessels form to supply it, and the surrounding muscle cells may grow larger and multiply in response. Evidence supporting this theory includes the fact that women who have had uterine surgery, such as cesarean delivery or dilation and curettage procedures, appear to be at higher risk.[4][6]
Another theory proposes that adenomyosis has developmental origins. According to this idea, certain stem cells present during embryonic development may differentiate incorrectly, leading to endometrial tissue being present in the wrong location from birth. This theory is supported by genetic studies showing altered expression of specific markers in women with adenomyosis, and by rare case reports of endometrial tissue found in women born without a uterus.[4]
Other less-established theories suggest that abnormal lymphatic drainage pathways or displaced bone marrow stem cells might explain the presence of misplaced endometrial tissue, though these ideas have less supporting evidence.[4]
Who is at Higher Risk?
While any woman who menstruates can develop adenomyosis, certain groups face higher risk. Age is a significant factor. The condition is most commonly diagnosed in women between 40 and 50 years old, though this may partly reflect historical diagnostic bias. Doctors are increasingly recognizing adenomyosis in younger women, particularly those in their 30s who present with abnormal bleeding or severe period pain.[2][3]
Women who have given birth at least once appear to be at increased risk. The process of pregnancy and childbirth may cause changes to the uterine wall that make it easier for endometrial tissue to invade. Similarly, women who have had previous uterine surgery face higher risk. Procedures such as cesarean sections, fibroid removal, or dilation and curettage may disrupt the normal barrier between the endometrial lining and the muscle wall.[2][6]
Women with endometriosis are also more likely to have adenomyosis. The two conditions often occur together, though they are separate diseases. Other risk factors include starting menstrual periods at age 10 or earlier, having shorter than average menstrual cycles, being obese, and having taken birth control pills. Women experiencing infertility are also diagnosed with adenomyosis more frequently than might be expected by chance.[6][7]
Symptoms and How They Affect Daily Life
One of the most challenging aspects of adenomyosis is that its symptoms vary dramatically from person to person. About one in three women with the condition experience no symptoms at all and may only discover they have it during imaging for another reason or after a hysterectomy.[2][3]
For those who do have symptoms, heavy menstrual bleeding, known as menorrhagia, is the most common complaint. Periods may last longer than usual, sometimes extending beyond seven days, and the bleeding can be so heavy that it soaks through pads or tampons quickly. Many women also pass blood clots during their periods. This excessive blood loss can lead to iron-deficiency anemia, causing fatigue, weakness, pale skin, and feeling cold all the time.[1][2]
Pain is another major symptom. Women with adenomyosis often experience severe menstrual cramps, medically termed dysmenorrhea, which may be much worse than typical period pain. The cramping can be so intense that it interferes with work, school, and daily activities. Unlike some menstrual pain that responds to over-the-counter medications, adenomyosis pain may be difficult to control. Some women also experience chronic pelvic pain that persists throughout their menstrual cycle, not just during their period.[1][3]
Pain during sexual intercourse, called dyspareunia, affects some women with adenomyosis. This can strain intimate relationships and reduce quality of life. Other symptoms include a feeling of pressure or fullness in the lower abdomen, bloating, and tenderness in the pelvic area. As the uterus enlarges due to the condition, women may notice that their abdomen looks or feels bigger, sometimes referred to as “adenomyosis belly.”[2][5]
The physical symptoms can lead to significant emotional and social impacts. Chronic pain and heavy bleeding can cause stress, anxiety, and depression. Women may miss work or social events to manage their symptoms, leading to feelings of isolation. The unpredictability of heavy bleeding can make it difficult to plan activities or travel. Partners and family members may struggle to understand the extent of suffering, which can strain relationships.[15]
Adenomyosis and Fertility
The relationship between adenomyosis and fertility is complex and not fully understood. Research suggests that women with adenomyosis may face greater difficulty becoming pregnant and may have a higher risk of miscarriage. The condition may affect fertility through several mechanisms. It can change the shape of the uterine cavity, making it harder for an embryo to implant. The inflammation associated with adenomyosis may create a hostile environment for pregnancy. Unusual uterine contractions and hormonal changes linked to the condition may also interfere with conception and pregnancy maintenance.[6][7]
Much of what is known about adenomyosis and fertility comes from studies of women undergoing in vitro fertilization treatment. These studies have shown lower pregnancy and birth rates in women with adenomyosis compared to those without the condition. Fertility specialists are actively researching ways to improve outcomes for women with adenomyosis who wish to become pregnant.[6]
Prevention Strategies
Because the exact cause of adenomyosis is unknown, there are no proven strategies to prevent the condition from developing. Unlike some diseases where lifestyle changes or vaccinations can reduce risk, adenomyosis appears to develop through mechanisms that are not yet well enough understood to prevent.[3][14]
However, women can take steps to reduce their risk of complications from adenomyosis, particularly anemia from heavy bleeding. Eating a diet rich in iron can help maintain healthy red blood cell levels. Foods high in iron include lean red meat, poultry, fish, beans, lentils, fortified cereals, and dark leafy greens like spinach. Vitamin C helps the body absorb iron, so including citrus fruits, tomatoes, and peppers in meals can be beneficial.[2]
Early recognition of symptoms is important. Women should not dismiss heavy or painful periods as normal, especially if symptoms worsen over time or begin to interfere with daily activities. Seeking medical attention promptly when symptoms develop allows for earlier diagnosis and treatment, which may prevent complications and improve quality of life. Regular gynecological checkups also provide opportunities for doctors to identify changes in the uterus that might suggest adenomyosis.[1][3]
How Adenomyosis Changes the Body
Understanding the physical changes that occur with adenomyosis helps explain why the condition causes such troublesome symptoms. At the cellular level, endometrial cells that should only exist in the uterine lining begin growing into the muscular wall. These cells continue to respond to the monthly hormonal fluctuations of estrogen and progesterone just as normal endometrial tissue does.[1][2]
During each menstrual cycle, rising estrogen levels cause the endometrial tissue to thicken in preparation for possible pregnancy. When pregnancy does not occur, hormone levels drop, triggering the tissue to break down and bleed. Normal endometrial tissue can exit the body through the cervix and vagina as menstrual flow. However, the endometrial tissue trapped within the muscle wall has no way to leave. This trapped blood and tissue cause inflammation and swelling, contributing to pain and the enlarged uterus characteristic of adenomyosis.[4]
The body responds to this abnormal tissue by developing new small blood vessels to supply it, a process called angiogenesis. The surrounding muscle cells may undergo hypertrophy, meaning they grow larger, and hyperplasia, meaning they increase in number. These changes cause the uterine wall to thicken. Over time, the combined effects of the misplaced endometrial tissue, inflammation, bleeding, and muscle changes can cause the uterus to significantly enlarge. In some cases, the uterus may become two or three times its normal size.[4][6]
Adenomyosis can be diffuse, affecting large areas of the uterus, or focal, concentrated in specific regions. Sometimes focal areas of adenomyosis are surrounded by muscle hypertrophy, creating what looks like a distinct mass called an adenomyoma, though unlike tumors, these masses do not have well-defined borders.[4]
The chronic inflammation associated with adenomyosis can affect the uterine environment in other ways. It may alter the normal contractility of the uterus, change hormone receptor expression, and affect the production of various growth factors and cytokines. These changes help explain why adenomyosis may impact fertility and why symptoms can be so varied among different women.[6]
