Endometriosis

IWBCA
Feb 14
10 min read

Endometriosis occurs when tissue that is similar to the lining of the uterus grows outside the uterine cavity, most often on pelvic structures such as the ovaries, peritoneum, and ligaments that support the uterus. These misplaced deposits respond to hormones, become inflamed with each cycle, and can cause chronic pelvic pain, heavy or painful periods, pain with sex or bowel movements, and fertility problems. Endometriosis is a chronic, estrogen-dependent inflammatory condition. Management typically involves hormonal suppression, pain control, surgical removal of visible disease, or a combination of these approaches tailored to a person’s symptoms, age, and fertility goals.

Overview

What is endometriosis?

Endometriosis is a condition in which tissue that resembles the uterine lining (endometrium) is found in places where it does not belong, most often within the pelvis and abdomen. These endometriosis lesions can form flat plaques, nodules, and cysts, such as ovarian endometriomas, sometimes called “chocolate cysts.” As they respond to cyclical hormones, they can bleed, inflame surrounding tissue, form scar tissue, and tether organs together. This can lead to painful and heavy periods, deep pelvic pain that may occur even outside menstruation, and difficulty getting pregnant.

Endometriosis is a chronic gynecologic condition in which endometrium-like tissue grows outside the uterine cavity on other organs and surfaces. Although this tissue is similar to the lining of the uterus, it is not identical and behaves differently in how it adheres, invades, and interacts with the immune system. Each menstrual cycle, these deposits can thicken and bleed in a confined space, triggering irritation, inflammation, and scarring. Over time, this process can cause persistent pain, organ dysfunction, and in some cases, distortion of pelvic anatomy.

Symptoms can affect many aspects of life. People may experience painful periods that start in adolescence, deep pelvic pain with intercourse, pain with bowel movements or urination around the time of their period, heavy or irregular bleeding, fatigue, and gastrointestinal symptoms that fluctuate with the cycle. In many, pain and other symptoms interfere with work, school, physical activity, sleep, and relationships. Infertility or subfertility can occur when inflammation, scarring, or distorted anatomy affects the ovaries, fallopian tubes, or the uterine environment.

Some of the most common places where endometriosis can develop include the:

Space behind the uterus in the cul-de-sac and on the uterosacral ligaments
Myometrium, the muscular layer of the uterine wall, is in a pattern referred to as adenomyosis
Ovaries, where cystic endometriomas can form
Peritoneum lining the pelvis and abdomen
Fallopian tubes and their surrounding tissues

Less common sites within the pelvis and abdomen include the:

Rectum and rectovaginal septum
Bladder and ureters
Small and large intestines
Vagina and cervix

Rarely, endometriosis is found outside the pelvis, including on the diaphragm, in the chest cavity, or in surgical scars. Thoracic endometriosis can cause chest pain or lung collapse that follows the menstrual pattern, and diaphragmatic disease can cause shoulder or upper abdominal pain with periods.

Endometriosis is common, affecting an estimated 1 in 10 people with a uterus during their reproductive years. It is frequently diagnosed in individuals in their 20s and 30s, but symptoms often begin in adolescence and may go unrecognized for years. Although endometriosis is a benign condition and not a cancer, it is a leading cause of chronic pelvic pain and infertility. With appropriate recognition and treatment, many people achieve significant symptom relief and can pursue personal, professional, and reproductive goals with far fewer limitations.

Symptoms

What are the symptoms of endometriosis?

Endometriosis is a chronic inflammatory condition, and its symptoms vary widely. Some people have severe, cycle-related pain and heavy bleeding. Others have minimal or no symptoms and are only diagnosed during evaluation for infertility or another pelvic problem. The most consistent symptom is pelvic pain that tends to cluster around menstruation, but many people develop pain throughout the month.

Common symptoms include:

Very Painful Menstrual Cramps (Dysmenorrhea): Cramps often begin several days before bleeding starts, peak during the period, and can continue after bleeding ends. Pain may be sharp, crampy, or felt as deep pelvic pressure and may radiate to the lower back, hips, or thighs. Many people report that period pain is progressively worse than it was in their teens.
Pelvic Pain Between Periods: Pelvic pain is frequently present outside of menstruation. It can be a constant dull ache, intermittent pelvic “stabbing” or burning, or a sense of heaviness or dragging in the pelvis. This non-menstrual pelvic pain is one of the key features of endometriosis.
Abdominal or Back Pain During or Between Periods: General lower abdominal pain and low back pain are common, especially in the days before and during menstruation. This pain may coexist with muscle tenderness and can limit physical activity, work, or sleep.
Heavy Menstrual Bleeding or Irregular Bleeding: Some people have heavy flow with clots, frequent “flooding” episodes, or periods that last longer than usual. Others experience spotting or light bleeding between periods or around ovulation. These bleeding changes often accompany pain but can also occur alone.
Pain During Sex (Dyspareunia): Deep pelvic pain with penetration, especially in certain positions, is common. Pain may be immediate or may worsen after intercourse and is often more intense in the days before and during a period. This symptom is strongly associated with disease in the cul-de-sac and uterosacral ligaments.
Pain with Bowel Movements or Urination (Dyschezia and Dysuria): Endometriosis on or near the rectum, bowel, bladder, or ureters can cause painful bowel movements, straining-related pain, rectal pressure, pain with urination, or a sense of incomplete emptying. These symptoms usually flare around menstruation and may be mistaken for irritable bowel syndrome or recurrent urinary infections.
Gastrointestinal Symptoms: Bloating, constipation, diarrhea, nausea, and cramping that worsen around the period are common. Many people are initially told they have “IBS,” and only later is endometriosis recognized as a driver of their cyclical digestive symptoms.
Infertility or Difficulty Conceiving: Endometriosis is frequently found during infertility work-ups. Inflammation, scarring, and adhesions can affect how eggs are released, how sperm and egg meet, and how an embryo implants, even when periods appear regular.
Fatigue and Other Systemic Symptoms: Chronic pain, poor sleep, anemia from heavy bleeding, and ongoing inflammation can lead to severe fatigue, dizziness during periods, headaches, and a general feeling of unwellness. Studies consistently show higher rates of anxiety, depression, and difficulty concentrating in people with endometriosis-related pain.
Shoulder, Chest, or Upper Abdominal Pain with Periods (Rare): In rare cases, endometriosis affects the diaphragm or the chest cavity. This can cause shoulder tip pain, chest pain, coughing blood, or shortness of breath that follows the menstrual pattern.

Some people have no obvious symptoms and only learn they have endometriosis when imaging or surgery is performed for another reason. Symptom intensity does not reliably track with disease extent: individuals with limited visible disease can have severe pain, while others with extensive lesions may have little or no pain.

Causes

What causes endometriosis?

The exact cause of endometriosis is not fully defined. Current research supports a multifactorial process involving the movement of menstrual blood and cells into the pelvis, local tissue transformation, stem cells, immune dysfunction, hormonal imbalances, and genetic susceptibility.

Key mechanisms include:

Retrograde Menstruation and Implantation: Menstrual blood and endometrial cells can flow backward through the fallopian tubes into the pelvic cavity during periods. In most people, the immune system clears these cells. In individuals who develop endometriosis, a combination of cell survival advantages, adhesiveness, and local immune changes enables these cells to implant on peritoneal surfaces and pelvic organs, forming lesions.
Coelomic Metaplasia and In-Situ Transformation: Cells lining the peritoneum and other pelvic structures can transform into endometrium-like tissue under specific hormonal or inflammatory conditions. This “metaplasia” explains endometriosis in locations not easily reached by retrograde flow and, in rare cases, in people without a uterus.
Stem Cell and Vascular Pathways: Stem or progenitor cells from the endometrium, bone marrow, or Müllerian remnants may circulate and differentiate into endometrium-like cells at distant sites. Lymphatic and blood vessels can also transport endometrial cells to the pelvic cavity or more remote locations such as the diaphragm or lungs.
Hormonal and Immune Dysregulation: Endometriosis is strongly estrogen-dependent. Lesions often overexpress estrogen-producing enzymes and show resistance to progesterone’s usual stabilizing effects. At the same time, the local immune environment is skewed toward chronic inflammation, with elevated cytokines, activated macrophages, oxidative stress, and impaired clearance of ectopic cells. This inflammatory microenvironment drives pain and interferes with fertility.

Overall, endometriosis is now viewed as a chronic, estrogen-dependent inflammatory disease that arises when susceptible tissue, immune, hormonal, and genetic pathways interact over time.

Risk Factors

What are the most common risk factors associated with endometriosis?

No single factor predicts who will develop endometriosis, but several features are associated with a higher risk:

Family History of Endometriosis: Having a first-degree relative with endometriosis is one of the strongest known risk factors.
Early Menarche and Prolonged Estrogen Exposure: An earlier age at first period and a longer span of menstruating years are linked with a higher risk.
Short Menstrual Cycles and Heavy or Prolonged Periods: Cycles shorter than about 27 days, bleeding lasting more than 7–8 days, and heavy menstrual flow have all been associated with increased risk, likely because they increase the volume and frequency of retrograde menstruation.
Low Parity or Never Having Been Pregnant: Having no prior pregnancies or few pregnancies is associated with a higher risk, whereas higher parity appears protective, possibly because pregnancy suppresses ovulation and menstruation for extended periods.
Anatomical or Outflow Abnormalities: Congenital conditions that obstruct menstrual outflow (e.g., a transverse vaginal septum or Müllerian anomalies) can lead to retrograde flow and increase the risk.
Early-Life and Environmental Factors: Emerging data suggest that preterm birth, low or high birth weight, certain in utero exposures (including diethylstilbestrol), and certain environmental toxicants may influence later risk, although these findings remain incompletely characterized.

These risk factors describe patterns seen in groups, not certainties for individuals. Many people with endometriosis lack these features, and many with these features never develop the disease.

Complications

What complications are most often associated with endometriosis?

Untreated or severe endometriosis can lead to a range of complications beyond pain during periods:

Chronic Pelvic Pain and Central Sensitization: Ongoing nociceptive input from lesions and inflamed tissues can induce changes in the nervous system, resulting in hypersensitivity of pain pathways. Pain may persist even when lesions are small or have been treated, and other areas of the body may become more sensitive to pain.
Infertility and Subfertility: Endometriosis is a major cause of infertility and can reduce the chance of natural conception and success with assisted reproductive technologies, particularly in those with advanced disease or ovarian endometriomas.
Bowel and Bladder Complications: Deep infiltrating disease can narrow or obstruct the bowel or ureters, leading to constipation, obstruction, blood in stool or urine, or kidney damage if ureteral obstruction goes unrecognized. Surgery is sometimes required to address these complications.
Adhesions and Organ Fixation: Chronic inflammation promotes scar formation that can bind organs, distort pelvic anatomy, and contribute to pain, bowel symptoms, and surgical complexity.
Ovarian Endometriomas and Malignancy Risk: Cystic ovarian endometriomas are common in endometriosis. Large or recurrent cysts can damage ovarian tissue and reduce ovarian reserve. A modestly increased lifetime risk of certain ovarian cancers (especially clear-cell and endometrioid types) has been reported in people with longstanding endometriosis, although the absolute risk remains low.
Mental Health and Quality-of-Life Impact: Chronic pain, fatigue, infertility, sexual pain, and repeated dismissal of symptoms are linked to higher rates of anxiety, depression, relationship strain, reduced work capacity, and social isolation.
Systemic Health Risks (Under Active Study): Large population studies suggest that people with endometriosis may have higher long-term risks of certain cardiovascular diseases and other chronic conditions, likely mediated by systemic inflammation, hormonal factors, and treatment exposures.

These complications do not occur in everyone with endometriosis, but they highlight why timely diagnosis, symptom control, and long-term follow-up are important.

Frequently Asked Questions

Is it genetic?

Genetics clearly influence risk, but they do not fully determine who develops endometriosis. Family and twin studies show that having an affected first-degree relative increases the risk of endometriosis several-fold, and genome-wide association studies have identified multiple susceptibility loci associated with hormone signaling, immune regulation, and cell adhesion.

Current evidence suggests that:

People with a mother, sister, or daughter with endometriosis have a substantially higher risk of developing it themselves.
Inherited variants create a background vulnerability that interacts with hormonal exposure, menstrual characteristics, early-life factors, and environmental influences to determine whether disease develops and how severe it becomes.

If a close biological relative has endometriosis, mentioning this to a clinician can help prompt earlier evaluation when symptoms arise, which may shorten the typical diagnostic delay.

Weight Management

Can endometriosis cause weight gain?

Endometriosis itself does not directly change body weight. However, several factors can make it feel as if the weight has increased:

Cyclical Bloating and Fluid Retention: Inflammation and hormonal shifts around the period can cause abdominal swelling and fluid shifts, sometimes called “endo belly,” which can make clothes fit tighter even without a true change in body weight.
Reduced Activity and Appetite Changes: Chronic pain, fatigue, and low mood can reduce physical activity and alter eating patterns, potentially contributing to gradual weight change over time.
Medication Effects: Some hormonal treatments, particularly certain progestins or GnRH-based therapies with add-back hormones, can be associated with changes in appetite, fluid retention, or body composition in a subset of patients.

If apparent weight gain or swelling is rapid, persistent, or distressing, it is important to consult a clinician to evaluate medication effects, metabolic issues, and other causes.

High-Risk Populations

Who can get endometriosis?

Endometriosis primarily affects people with a uterus and functioning ovaries during their reproductive years. Global estimates suggest that approximately 10% of individuals of reproductive age are affected, corresponding to approximately 190 million people worldwide.

Key patterns include:

It most commonly presents in people in their 20s and 30s, but symptoms often start in adolescence and may be dismissed as “bad periods” for years.
It can occur in teenagers, including those soon after menarche, particularly when pain is severe, progressive, or associated with gastrointestinal or urinary symptoms.
Symptoms often improve after natural menopause, but the disease can persist, particularly in those using estrogen therapy, and rare cases are reported even after menopause.

Endometriosis can also affect transgender men and nonbinary people assigned female at birth, and barriers to care in these groups can contribute to delayed diagnosis and undertreatment.

How does endometriosis cause infertility?

Endometriosis can impair fertility through several interconnected pathways:

Mechanical Disruption of Pelvic Anatomy: Adhesions and scar tissue can tether the ovaries, fallopian tubes, and uterus in abnormal positions, or block the tubes, making it harder for egg and sperm to meet and for an embryo to travel into the uterus.
Inflammatory Peritoneal Environment: Pelvic fluid in endometriosis often contains elevated inflammatory mediators and reactive oxygen species, which can impair sperm function, damage eggs, and interfere with fertilization and early embryo development.
Effects on Ovarian Reserve: Ovarian endometriomas and their surgical treatment can reduce the number of remaining follicles and eggs in the ovary, lowering ovarian reserve and shortening the reproductive window for some patients.
Altered Endometrial Receptivity: Endometriosis is associated with molecular changes in the uterine lining, including altered hormone receptor expression and inflammatory signaling, which may reduce the likelihood of successful embryo implantation.

Despite these mechanisms, many people with endometriosis do conceive, both spontaneously and with fertility treatment. Understanding how endometriosis affects an individual’s anatomy, ovarian reserve, and uterine environment helps guide decisions about the timing of pregnancy attempts, use of medical suppression, and when to consider assisted reproductive technologies.

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