Endometriosis — tissue similar to the uterine lining growing outside the uterus — affects approximately 1 in 10 women in the UK and is a significant cause of subfertility. It is also frequently underdiagnosed: the average time from symptom onset to diagnosis in the UK is currently around 7–8 years.

For patients with endometriosis who are trying to conceive, the relationship between the condition and fertility is complex and stage-dependent. IVF is often recommended when simpler approaches have not worked, but the impact of endometriosis on IVF outcomes — and how to manage it — is more nuanced than a simple "endometriosis = harder to treat."

How Endometriosis Affects Fertility

Endometriosis impairs fertility through several mechanisms, which vary by stage and location:

Peritoneal disease (Stage I–II). Superficial peritoneal implants and mild adhesions alter the peritoneal environment. Inflammatory cytokines, altered follicular fluid composition, and immune changes may impair egg quality and fertilisation. The effect is real but relatively modest.

Ovarian endometriomas (Stage III). Endometriotic cysts on the ovaries ("chocolate cysts") are directly damaging to adjacent ovarian tissue. Studies show that endometriomas reduce ovarian reserve — AMH is lower in patients with endometriomas than in matched controls, and the effect is proportional to cyst size and bilateral involvement. Surgery to remove endometriomas also reduces ovarian reserve (because some healthy ovarian tissue is always removed along with the cyst wall), creating a difficult dilemma about whether to operate before IVF.

Deep infiltrating endometriosis (DIE) and adhesions (Stage III–IV). Severe adhesions can distort pelvic anatomy, blocking fallopian tubes and making natural conception very unlikely. Hydrosalpinges (fluid-filled, damaged tubes) associated with severe adhesive disease may actively impair IVF implantation rates and typically warrant surgical removal or occlusion before IVF.

Adenomyosis. When endometriosis-like tissue invades the muscle of the uterine wall (adenomyosis), implantation rates in IVF are substantially reduced. Adenomyosis is increasingly recognised as co-existing with endometriosis and may be an independent factor in IVF failure.

Should Endometriomas Be Operated on Before IVF?

This is one of the most contested clinical questions in reproductive medicine. The competing considerations:

Arguments for surgery first:

  • Endometriomas may impair egg quality in the affected ovary
  • Large endometriomas (>4cm) can obstruct egg collection
  • Removing the endometrioma before stimulation may improve access to follicles and reduce contamination of follicular fluid

Arguments against surgery before IVF:

  • Surgery consistently reduces ovarian reserve — each operation further depletes functional ovarian tissue
  • In patients with already-reduced reserve, surgery may reduce the number of eggs available in the IVF cycle more than the endometrioma itself would
  • A 2014 Cochrane review found no evidence that surgical treatment of endometriomas before IVF improved live birth rates

The current consensus among specialist centres is nuanced: surgery is generally recommended for symptomatic endometriomas, bilateral endometriomas, those growing rapidly, or those obstructing follicle access. For patients with a single small-to-moderate endometrioma and good ovarian reserve, proceeding to IVF without surgery is a reasonable approach. This decision should be made with a consultant who has endometriosis expertise.

IVF Outcomes in Endometriosis

IVF success rates in endometriosis patients vary significantly by stage and by whether the condition has affected ovarian reserve:

Stage I–II (minimal to mild endometriosis): IVF outcomes are broadly similar to age-matched patients without endometriosis in many studies. The main challenge may be slightly lower egg numbers.

Stage III–IV with endometriomas: Lower ovarian reserve typically means fewer eggs per cycle. Multiple studies show lower live birth rates per cycle in patients with ovarian endometriosis compared to the general IVF population. However, if AMH and AFC are reasonable, outcomes can be good.

Adenomyosis: This is associated with substantially lower implantation rates and is the most challenging subgroup for IVF.

The HFEA does not publish outcome data broken down by endometriosis diagnosis, but specialist centres report that patients with severe endometriosis may need more IVF cycles to achieve a live birth than patients with other diagnoses.

For interpreting success rate data generally, see HFEA success rates explained.

IVF Protocol Modifications for Endometriosis

Several protocol modifications have evidence support for endometriosis patients:

Long down-regulation (GnRH agonist pre-treatment). A period of 3–6 months of GnRH agonist down-regulation before starting IVF stimulation has been studied in endometriosis patients. Some meta-analyses suggest improved clinical pregnancy rates with pre-IVF down-regulation in endometriosis patients, thought to work by suppressing active implants and improving endometrial receptivity. The evidence is not definitive, and the extended timeline is a significant consideration.

Freeze-all strategy. Where adenomyosis is present or where the endometrial environment is suspected to be suboptimal, a freeze-all strategy and separate FET cycle may improve implantation rates compared to a fresh transfer. See frozen embryo transfer guide.

Surgical treatment of hydrosalpinges. Where damaged, fluid-filled tubes are present alongside endometriosis, occluding or removing them before IVF is strongly recommended — the evidence that hydrosalpinges reduce IVF implantation rates is robust.

NHS IVF Access with Endometriosis

Endometriosis does not automatically confer NHS IVF eligibility, but it is a recognised clinical cause of infertility that counts within most ICB eligibility criteria. NHS treatment for endometriosis itself (surgery, hormonal treatment) is separate from NHS IVF eligibility, which is governed by the ICB's commissioning policy.

Patients with severe endometriosis affecting tubes and ovaries may be referred to specialist centres rather than a standard fertility unit. If your ICB has denied IVF funding on the basis that your infertility has not been sufficiently investigated or treated, and endometriosis is the likely cause, the Individual Funding Request (IFR) route may be available — see how to appeal an NHS IVF refusal.

Check your ICB's commissioning policy at nestie.co/nhs.

Frequently Asked Questions

Q: Does having endometriosis mean I will definitely need IVF?

A: No. Many people with endometriosis conceive naturally or with lower-complexity treatments. Stage and location matter greatly. Patients with mild peritoneal endometriosis and patent tubes often have near-normal fertility. IVF is indicated when tubes are blocked, when simpler treatments have failed, when ovarian reserve is significantly impaired, or when the duration of infertility and age make more proactive treatment appropriate.

Q: My endometrioma is small (2cm). Should I have it removed before IVF?

A: For a single endometrioma of 2cm in a patient with good ovarian reserve, many specialist centres would advise proceeding to IVF without prior surgery, as the surgical risk to reserve outweighs the likely benefit. For larger, symptomatic, or bilateral endometriomas, the calculus changes. This is a decision to make with a fertility specialist who has reviewed your specific AMH, AFC, and imaging.

Q: Can I improve my IVF chances if I have endometriosis?

A: Optimising overall health and reducing inflammation are reasonable approaches — maintaining a healthy weight, anti-inflammatory diet patterns, and avoiding smoking are all worthwhile. Some specialists use a longer down-regulation protocol before IVF for endometriosis patients. Discuss with your consultant whether any specific protocol modifications are appropriate for your degree of disease.

Q: Does endometriosis cause poor egg quality?

A: There is evidence that peritoneal endometriosis alters the follicular environment in ways that may affect egg quality. Ovarian endometriomas in particular are associated with reduced ovarian reserve and potentially impaired egg quality in the affected ovary. However, many patients with endometriosis produce good-quality eggs and have successful IVF cycles.

Q: What is adenomyosis and does it affect IVF?

A: Adenomyosis is the presence of endometrial-like tissue within the muscular wall of the uterus (myometrium), rather than on pelvic surfaces. It is associated with enlarged, tender uterus, heavy periods, and dysmenorrhoea. Adenomyosis substantially reduces IVF implantation rates — studies show 20–30% lower live birth rates compared to patients without adenomyosis. It is increasingly recognised as distinct from endometriosis and as an independent contributor to IVF failure. If adenomyosis is identified on ultrasound, discuss with your consultant whether a specific treatment or protocol modification is appropriate.

This article is for information only and does not constitute medical advice. Always discuss endometriosis management and fertility treatment with a specialist with expertise in both areas.