Endometriosis Overview

Endometriosis is a common health problem for women who menstruate.¹ In women with endometriosis, patches of tissue that resemble the endometrium are found outside the uterus. These lesions are most commonly found on the ovaries or the fallopian tubes,² but they can also grow in other parts of the body, including the bladder or lungs.^{3 , 4} Pain is a primary symptom, although its severity varies widely and does not reliably reflect the extent or location of lesions. Endometriosis-related pain may result from hormone-driven inflammation and bleeding of endometriosis tissue, formation of scar tissue, and effects on nearby nerve cells.

The causes of endometriosis are not fully understood.² Endometriosis is a major contributor to infertility and may also be associated with irregular menstrual cycles. Symptoms often resolve after menopause as estrogen levels decline, although some women may experience recurring symptoms.

Endometriosis primarily affects women because it is linked to the female reproductive system; however, its effects extend beyond the pelvis. Endometriosis commonly co-occurs with other gynecologic conditions, such as uterine fibroids, as well as chronic pain syndromes, gastrointestinal and bladder conditions, and mood disorders. Research has also identified associations between endometriosis and certain cancers, autoimmune diseases, and cardiovascular disease.⁵

Diagnosing endometriosis remains challenging. Symptoms often overlap and co‑occur with other conditions, which can lead to misdiagnosis or prolonged evaluation. Although a definitive diagnosis relies on laparoscopy,⁶ an invasive surgical procedure that may be difficult to access, many providers will begin treatment for presumed endometriosis after assessing a patient's symptoms, medical history, and physical and imaging exams. Current treatments, including hormone therapy and pain medication, can help manage symptoms⁷ but do not cure or reverse the disease.¹ Because the available treatments may affect fertility, managing endometriosis often requires balancing pain control, disease suppression, and reproductive goals with the need for fertility preserving approaches.⁸ Understanding how endometriosis and pain are related is an active area of research, as is promoting earlier diagnosis using improved noninvasive tools that include transvaginal ultrasound and magnetic resonance imaging.⁹ Because the effects of endometriosis extend beyond physical symptoms to include substantial psychological and social burdens—such as reduced quality of life, emotional distress, impaired relationships, lost productivity, and economic costs—current research priorities are considering women’s holistic needs.⁸

The Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) is a key organization for research on endometriosis at NIH. Several divisions within NICHD are working to better understand the causes, diagnosis, and treatment of endometriosis.¹⁰ Within the Division of Extramural Research, the Gynecologic Health and Disease Branch and the Fertility and Infertility Branch are investigating ways to improve women’s reproductive health, including studying the normal function of the endometrium and the causes of gynecological disorders like endometriosis. In addition, the Endometriosis: Natural History, Diagnosis, and Outcomes (ENDO) study allowed researchers in the Division of Population Health Research to assess the role of endocrine-disrupting chemicals in endometriosis.⁶

Investigators funded through the National Centers for Translational Research in Reproduction and Infertility developed a gene‑based “diagnostic classifier,” a computational model that analyzed patterns of gene expression in endometrial tissue. In this initial study, the classifier distinguished endometriosis status and disease stage with reported accuracies of 90% to 100%.¹¹ Building on this early demonstration that gene‑expression patterns could distinguish endometriosis, subsequent studies have used genomic and computational methods to further examine molecular signatures linked to the disease.¹² Because endometriosis is typically diagnosed through surgical laparoscopy, this research underscores ongoing efforts to find less invasive ways to improve diagnosis.