Not All Endometriosis Carries the Same Fertility Prognosis

What a national Finnish study of 9,590 surgically diagnosed nulliparous women teaches us about age, phenotype, and why ovarian disease may carry the greatest reproductive cost.

 

Study Overview & Headline Findings

• Study Design: National register study of 9,590 nulliparous women in Finland whose endometriosis was first surgically diagnosed between 1998 and 2012.

• Headline Finding: Just over 1 in 2 women had a first birth after diagnosis, but outcomes differed meaningfully by phenotype and age.

• Best Prognosis: Peritoneal disease: about 2 in 3 had a first birth after diagnosis.

• Most Concerning Signal: Ovarian disease: fewer than 1 in 2 had a first birth, and this group was diagnosed at the oldest median age.

Why This Paper Matters

Population studies rarely give clinicians and patients a usable fertility map after a confirmed diagnosis of endometriosis. This paper does. Tuominen and colleagues followed 9,590 women in Finland who had never previously given birth and whose first diagnosis of endometriosis was made at surgery.

The message is both reassuring and cautionary: the overall outlook after diagnosis was better than many patients fear, but the prognosis was not uniform. Age mattered enormously, and subtype mattered as well. Peritoneal disease had the most favorable first-birth outcomes. Ovarian disease had the worst.

Too much of the fertility discussion around endometriosis is still driven by anecdote, referral bias, or IVF-only cohorts. This study is different because it is population-based, includes multiple phenotypes, and looks specifically at women who were nulliparous at the time of first surgical diagnosis. That makes it clinically relevant when counseling patients who ask a simple but urgent question: what happens to fertility after endometriosis is finally identified?

The Numbers Patients Can Understand

Subtype	Women	First birth	Plain-English take	Rate / 100 PY
Overall	9,590	5,184	Just over 1 in 2	7.67
Peritoneal	3,146	1,962	About 2 in 3	9.44
Ovarian	3,020	1,380	Just under 1 in 2	6.21
Deep	659	384	About 3 in 5	8.14
Combined / other	2,765	1,458	Just over 1 in 2	7.32

Table 1. Study outcomes by phenotype, translated into patient-friendly language. PY = person-years.

The phenotype differences are striking. After surgical diagnosis, about 2 in 3 women with peritoneal endometriosis had a first birth. That fell to about 3 in 5 for deep disease, just over 1 in 2 for combined or other disease, and to just under 1 in 2 for ovarian disease. In other words, ovarian endometriosis was not simply a little worse – it was the least favorable fertility phenotype in the study.

Age at Diagnosis Was Just as Important

The age curves are probably the most clinically important part of the paper. The annualized first-birth rate was about 1 first birth per 10 women-years when surgery occurred before age 30, about 1 per 12 women-years at ages 30-34, about 1 per 26 women-years at ages 35-39, and only about 1 per 149 women-years after age 40.

The message is not subtle: once diagnosis drifts into the later reproductive years, the fertility penalty becomes severe.

Age at surgery	Rate / 100 PY	Plain-English translation
<=24	10.3	About 1 first birth per 10 women-years
25-29	9.85	About 1 first birth per 10 women-years
30-34	8.43	About 1 first birth per 12 women-years
35-39	3.91	About 1 first birth per 26 women-years
40-49	0.67	About 1 first birth per 149 women-years

Table 2. Age-related annualized first-birth rates for the full cohort.

What the Graphs Show

The two Kaplan-Meier figures make the same point visually. The age figure shows a dramatic separation very early in follow-up: women diagnosed before 30 continue to accumulate first births, whereas the curve for women diagnosed at 40 or older barely moves. The phenotype figure shows that peritoneal disease remains the most favorable curve over time and ovarian disease the least favorable.

Notably, deep disease does not emerge as the worst fertility phenotype in this dataset, which is a useful corrective to the simplistic assumption that the deepest disease must always carry the worst reproductive prognosis.

Why Ovarian Disease Likely Performed Worst

This is the section of the paper with the most important clinical implications. Women with ovarian endometriosis were the oldest at diagnosis, with a median age of 32.5 years, compared with 30.4 years for peritoneal disease. That matters because age alone reduces reproductive potential. But age probably does not explain everything.

The authors point to a plausible dual hit. First, ovarian endometriosis may be diagnosed later because it can be less symptomatic, so patients may not come to surgery until fertility is already under pressure. Second, both the disease itself and ovarian surgery can compromise ovarian reserve. The paper specifically cites literature showing that excision of an endometrioma can remove functioning ovarian tissue, and that ovarian reserve may already be reduced simply by the presence of the endometrioma.

What this study does not prove is that every woman with ovarian disease got there because her endometriosis was ‘allowed to progress,’ or that surgery itself caused the poorer outcomes. Register studies cannot answer that level of mechanistic detail. But the clinical warning is still clear: when endometriosis is recognized late, especially once it involves the ovary, the fertility cost may be much harder to reverse.

 

The Practical ESSI Takeawy

For an endometriosis center focused on both pain and reproduction, the message is straightforward. Early recognition matters. Thoughtful phenotyping matters. Fertility-preserving ovarian surgery matters even more.

This paper supports a strategy in which clinicians do not treat all endometriosis as though it carries the same reproductive implications. A woman with peritoneal disease at 27 is not the same fertility patient as a woman with bilateral ovarian disease diagnosed at 35.

It also supports a second point: deep endometriosis should not automatically be framed as a reproductive dead end. In this study, about 3 in 5 women with deep disease had a first birth after diagnosis. That does not minimize the complexity of deep disease, but it does remind us that expert management can still produce meaningful reproductive outcomes.

Finally, the subgroup with prior infertility is encouraging. About 2 in 3 women who already carried an infertility diagnosis had a first birth after diagnosis, and their median time to first birth was just under 2 years. That finding likely reflects both diagnosis and access to treatment. It is hopeful, but it is also a reminder that the value of a diagnosis is greatest when it changes what happens next.

Commentary from Dr. Andrea Vidali

“What this study adds is not the basic idea that endometriosis affects fertility; we already knew that. What it gives us is something much more usable: a phenotype-specific, population-level picture of first birth after surgical diagnosis in women who had never yet had a child. That is clinically important because it moves the conversation from abstraction to prognosis.

The most important signal is that ovarian endometriosis was the least favorable reproductive phenotype in this cohort. Fewer than 1 in 2 women with ovarian disease had a first birth after diagnosis, compared with about 3 in 5 with peritoneal disease and about 3 in 5 with deep disease. In other words, deep disease was not the worst fertility phenotype here; ovarian disease was.

The ovarian group was also diagnosed later, which suggests that by the time many of these women came to surgery, reproductive time had already been lost. That finding matters because ovarian disease may carry a dual burden. The endometrioma itself may already be associated with lower ovarian reserve, and ovarian surgery, if not done with great care, can further reduce functioning ovarian tissue.

This paper does not prove that surgery caused the poorer outcomes, and it does not prove that every case of ovarian disease simply represents progression. But it strongly supports a more fertility-preserving mindset: diagnose earlier, individualize timing, and avoid treating ovarian disease as though it were biologically neutral.

The age data are just as powerful. Across phenotypes, fertility prospects dropped sharply once diagnosis occurred at 35 or older. That means the reproductive cost of endometriosis is not only about how severe the disease looks in the operating room; it is also about time. A woman diagnosed at 27 with peritoneal disease is not facing the same reproductive reality as a woman diagnosed at 35 with ovarian disease.

Another reassuring message is that infertility plus endometriosis is not a hopeless combination. In this study, nearly 2 in 3 women who already had an infertility diagnosis still achieved a first birth after endometriosis was diagnosed, and the median time to first birth was just under 2 years.

From a reproductive endocrinology and reproductive surgery perspective, the practical lesson is clear: not all endometriosis carries the same fertility prognosis, ovarian disease deserves particular caution, and earlier diagnosis may preserve options before the ovary becomes the battleground.”

References

• Tuominen A, Saavalainen L, Saavalainen J, Niinimäki M, Gissler M, Härkki P, Heikinheimo O. First birth rates after surgically verified subtypes of endometriosis-a national register study of 9,590 women from Finland. Fertil Steril. 2026;125(4):660-670. doi:10.1016/j.fertnstert.2025.10.025.

• Raffi F, Metwally M, Amer S. The impact of excision of ovarian endometrioma on ovarian reserve: a systematic review and meta-analysis. J Clin Endocrinol Metab. 2012;97:3146-3154.

• Muzii L, Di Tucci C, Di Feliciantonio M, et al. Antimullerian hormone is reduced in the presence of ovarian endometriomas: a systematic review and meta-analysis. Fertil Steril. 2018;110:932-940.e1.