Endometriosis

Endometriosis is the presence of endometrium-like tissue outside the uterine cavity, most often on the pelvic peritoneum, ovaries, and uterosacral ligaments. Within tubal and uterine infertility it is an important anatomic and inflammatory contributor to subfertility: it can distort pelvic anatomy, form ovarian endometriomas, and create an inflammatory environment that impairs gamete function and implantation. This entry focuses on its relationship to fertility; a sibling entry covers endometriosis as a gynaecologic disorder more broadly.

Definition

Endometriosis is a chronic, oestrogen-dependent condition defined by endometrium-like glands and stroma located outside the uterus, which in the fertility context contributes to subfertility through anatomic distortion, ovarian involvement, and pelvic inflammation.

Scope

This entry addresses endometriosis as a cause of female infertility — its lesions, the mechanisms linking it to reduced fecundity, and how it is positioned among anatomic infertility factors. It is reference-educational and non-prescriptive. The broader gynaecologic disease entry sits under benign gynecologic disorders and is cross-linked.

Core questions

• By what mechanisms does endometriosis impair fertility?
• How do disease stage and lesion type (peritoneal, ovarian endometrioma, deep infiltrating) relate to fecundity?
• How is endometriosis-associated infertility distinguished from other anatomic causes?

Key concepts

• Endometrium-like tissue outside the uterus
• Ovarian endometrioma
• Deep infiltrating endometriosis
• Pelvic adhesions and anatomic distortion
• Inflammatory pelvic environment
• Oestrogen dependence
• Disease staging

Key theories

Retrograde menstruation (implantation) theory

Endometrial tissue refluxed through the tubes during menstruation implants and grows on pelvic surfaces; this classic hypothesis explains the typical pelvic distribution of lesions, though it does not account for all cases and is complemented by immunologic and stem-cell hypotheses.

Mechanisms

Endometriosis is thought to reduce fertility through several overlapping routes. Anatomically, peritoneal and deep lesions provoke adhesions that distort the tubo-ovarian relationship and impair oocyte pick-up; ovarian endometriomas can damage ovarian tissue and reserve. Biologically, the disease creates a chronic inflammatory peritoneal environment with altered cytokines and oxidative stress that may impair sperm function, fertilisation, and embryo quality, and it is associated with reduced endometrial receptivity. The retrograde menstruation hypothesis (refluxed endometrial tissue implanting on pelvic surfaces) is the classic account of how lesions arise, and the ESHRE guideline (Becker et al., 2022) summarises the disease and its links to infertility.

Clinical relevance

Endometriosis is a common finding among women evaluated for infertility and is a recognised anatomic-inflammatory cause of subfertility. This entry explains those associations for educational orientation. Decisions about investigation or management of endometriosis-associated infertility are clinical and follow current guidelines such as those of ESHRE; they are not addressed prescriptively here.

Epidemiology

Endometriosis affects roughly 10% of reproductive-age women and is markedly more common among women presenting with infertility than in the general population. Severity ranges from isolated peritoneal implants to extensive deep infiltrating disease and endometriomas; the association with subfertility is present across stages, though the strength of the causal contribution varies (Becker et al., 2022; Carson & Kallen, 2021).

History

Descriptions of ectopic endometrial tissue accumulated through the nineteenth and early twentieth centuries, and John Sampson's articulation of the retrograde menstruation hypothesis in the 1920s gave the field its enduring (if incomplete) pathogenic model. Laparoscopy later made direct diagnosis and staging possible, and successive society guidelines, most recently the 2022 ESHRE guideline, have consolidated the evidence on endometriosis and infertility.

Debates

How should ovarian endometriomas be handled in women seeking fertility?

Surgical excision of endometriomas can relieve symptoms and confirm diagnosis but risks reducing ovarian reserve; balancing this against expectant or assisted-reproduction approaches remains debated and individualised.

Seminal works

• becker-2022
• carson-2021

Frequently asked questions

How does endometriosis cause infertility?

It can distort pelvic anatomy and impair oocyte pick-up through adhesions, damage the ovary via endometriomas, and create an inflammatory pelvic environment that reduces gamete function and implantation; the relative contribution varies between women.

Does this entry differ from the general endometriosis entry?

Yes. This topic focuses on endometriosis as a cause of infertility within reproductive medicine; a separate cross-linked entry under benign gynecologic disorders treats endometriosis as a gynaecologic disease more broadly.