Endometriosis and Fertility: Ovarian Reserve and Surgery

Endometriosis reduces fertility mainly by fixing and damaging the fallopian tubes, disrupting ovulation, inflaming the pelvis and making the uterine lining less receptive, not usually by lowering ovarian reserve. Large endometriomas (ovarian cysts of endometriosis), and surgery on them, can destroy ovarian tissue, so for most young women medical treatment comes first and surgery is kept for clear indications.

Dr. Tripti Sharan, Senior Director - Obstetrics & Gynaecology and Head – High Risk Pregnancy, BLK-Max Super Speciality Hospital, New Delhi, India, describes infertility as the most common presenting symptom of endometriosis after pain. Much of the discussion at her masterclass turned on the trade-offs fertility forces: when to suppress the disease, when to operate, how to protect the ovaries, and when to freeze eggs. This article sets out her reasoning. The complete guide to endometriosis covers the condition as a whole.

How endometriosis causes infertility

Asked whether endometriosis harms fertility by reducing AMH (anti-Müllerian hormone, a blood marker of the egg supply), Dr. Sharan answered that it can, but usually does not. Infertility in endometriosis has many causes at once: "It is not a single factor."

1. The tubes stop working. A healthy fallopian tube is mobile. It picks up the egg as it is released from the ovary and carries it inward to where fertilisation takes place. When endometriosis and its adhesions fix the tube to surrounding structures and inflame it, the tube can no longer pick up the egg and becomes functionally useless.
2. The ovaries stop releasing eggs. Endometriosis in the ovary causes hormonal imbalance. Eggs may not mature properly, and follicles may grow but fail to rupture and release the egg.
3. The pelvis becomes hostile. The inflamed peritoneal lining creates an environment unsuitable for conception.
4. Sperm are damaged. Inflammatory substances secreted by endometriotic tissue can destroy sperm.
5. The uterus resists implantation. The endometrium itself can become unfit to receive a fertilised embryo.

This multiplicity explains why no single intervention restores fertility in every woman, and why the history and examination must guide the plan.

When an endometrioma does affect ovarian reserve

A woman is born with a fixed number of follicles, held within the ovarian tissue (the stroma). An endometrioma growing inside the ovary destroys the surrounding follicles as it enlarges. If the cyst replaces most of the ovary, the stroma and the follicles within it are lost, and ovarian reserve falls.

Dr. Sharan described a second mechanism: follicles that survive in a damaged ovary do not grow well. A follicle that does not develop each month means anovulation, and therefore no chance of conception that cycle. Both effects, destroyed follicles and functionless ones, contribute to infertility and to falling reserve. She stressed, however, that this is not the usual story; in most women with endometriosis, the causes of infertility are the tubal, ovarian, peritoneal and uterine factors above, not a low AMH.

Why endometrioma surgery can make fertility worse

Surgery on an endometrioma can reduce fertility because it removes healthy ovarian tissue and creates new adhesions. A doctor in the session asked why operating on an endometrioma can paradoxically worsen fertility. Dr. Sharan called it "a very, very good question" and gave two reasons.

First, operating on the ovary removes or burns healthy ovarian tissue along with the cyst: "the more you burn it, the more you destroy the follicles." Second, surgery creates adhesions. Endometriosis already causes infertility through adhesions, and every operation adds to them.

Her conclusion is that a young woman who has not completed her family and does not have a very large cyst, or who has endometriosis elsewhere such as on the bowel, should not automatically be operated on. Surgery should be reserved for:

• a larger lesion;
• disease causing adhesions or severe pain;
• infertility where the tubes are suspected to be blocked or stuck and need to be released.

"Otherwise, in majority patients, the first line of treatment should always be medical," she said. The aim is to avoid destroying normal ovarian tissue unnecessarily.

Managing an endometrioma in a woman planning pregnancy

For a woman trying to conceive who is found to have an ovarian endometrioma, Dr. Sharan's approach depends on size and symptoms.

Cyst under about 5 centimetres, few symptoms. She may do nothing to the cyst. The woman is supported and encouraged to try for pregnancy; once she conceives, her periods stop and the endometriosis regresses. Mild pain can be managed with simple painkillers. Contraceptive pills are not appropriate, since they prevent conception.

A progestogen as a bridge. Micronised progesterone or dydrogesterone can treat the endometriosis while she tries to conceive. Both are safe in pregnancy and provide luteal phase support, the hormonal support of the second half of the cycle that early pregnancy depends on, which Dr. Sharan considers an important factor in infertility in these patients.

A woman who can wait. If she can wait five to six months and pain is the main problem, Dr. Sharan offers suppression first: contraceptive pills for about six months, or dienogest, which stops periods for five or six months, and then attempts at conception. The suppression controls pain; it does not raise the chance of conceiving afterwards.

Large, symptomatic or widespread disease. If the lesions are very big, very symptomatic, or she is not ready to wait, there is no alternative to surgery. A woman planning a pregnancy cannot be kept waiting indefinitely. The operation must then be performed carefully, with minimal thermal damage: the surgeon works only around the endometriotic cyst and clears the adhesions, which are themselves preventing pregnancy. "We have to weigh the pros and cons," she said.

GnRH suppression and spontaneous fertility

GnRH suppression rules out conception while it is given, but it usually makes the lesions regress and opens a window for natural conception once it stops. A doctor from Uganda asked whether suppressing endometriosis with GnRH therapy improves the chance of natural conception afterwards. Dr. Sharan's answer frames the treatment as a time-limited tool. Endometriosis is a continuous disease; GnRH injections are always temporary, never lifelong, and she generally gives them for about six months. A woman cannot conceive while taking them.

The lesions usually regress during treatment, and pregnancy can be attempted once the injections stop, before the disease starts growing again. Trials have not shown, however, that suppressing the ovaries beforehand improves the chance of natural conception, and current European guidance (ESHRE, 2022) advises against hormonal suppression solely to improve fertility, because it delays the attempt at pregnancy. She uses GnRH suppression particularly for women who are not good candidates for surgery or who want to conserve their fertility.

Freezing eggs before endometriosis surgery

When a woman with severe disease decides to have surgery, the risk to her ovarian reserve raises the question of egg freezing beforehand. Dr. Sharan considers it a genuine option, with the decision based on three factors:

• Her age.
• Her current AMH level.
• The extent of the disease.

If the disease is very extensive, surgeons have sometimes ended up removing the whole mass, carrying most of the ovarian tissue with it. Where the disease is extensive, and particularly when it affects both ovaries, she regards egg freezing as "a very attractive option" that should be offered before surgery. Women who later need assisted conception can see the cost of IVF as a reference point.

Endometriomas during pregnancy

Once a woman with an endometrioma conceives, the cyst rarely causes difficulty. Small cysts usually regress because there are no periods, and even cysts of 5 or 6 centimetres usually cause no problem. Dr. Sharan was clear that the cyst does not harm the pregnancy or the baby; the risks she described are mechanical and confined to larger cysts, which can twist (torsion) or rupture and cause pain. Population studies do link endometriosis itself with modestly higher rates of some pregnancy complications, such as placenta praevia and preterm birth.

Which endometriosis treatments are compatible with fertility

Several endometriosis treatments are themselves incompatible with conception while in use, which shapes the order of treatment for women who want a family:

• Combined oral contraceptive pills prevent pregnancy; they are used before, not during, attempts to conceive.
• The Mirena intrauterine device prevents conception while in place, so Dr. Sharan reserves it for women who have completed their family.
• GnRH agonists prevent conception during treatment; the opportunity comes after they stop.
• Micronised progesterone and dydrogesterone are the exceptions: safe in pregnancy and supportive of it.

For women heading towards IVF, the question of which endometriosis and tubal problems to correct surgically first is covered in endometriosis and tubal surgery before IVF from Dr. Shelly Singh's masterclass. The full range of medical and surgical options is in the treatment article, and the audience's fertility questions, including those on ovarian reserve and egg freezing, are answered in the Live Discussion.