Ovarian Cysts: When to Treat, When to Watch, and What It Means for Fertility

Ovarian cysts are among the most common gynaecological findings in women of all ages. They are detected routinely on pelvic ultrasound — sometimes as incidental findings when the ultrasound is performed for a completely different reason, sometimes as the explanation for symptoms the woman has been experiencing. The natural response to being told you have an ovarian cyst is anxiety. The clinical reality is that the vast majority of ovarian cysts require no treatment at all — but distinguishing those that can be safely observed from those that require surgery demands specialist judgment.

Types of Ovarian Cysts

Functional Cysts

Functional cysts are the most common type — and the one most likely to resolve without any intervention. They arise from normal physiological processes:

• Follicular cysts: When a follicle fails to rupture at ovulation and continues to grow. These are thin-walled, unilocular (single compartment), and typically resolve within 1 to 3 menstrual cycles.
• Corpus luteum cysts: The corpus luteum (the progesterone-producing structure that forms after ovulation) develops into a cyst. They can occasionally bleed internally, causing acute pelvic pain — but most resolve spontaneously within 4 to 8 weeks.

Functional cysts do not require surgery unless they rupture with significant haemorrhage, cause haemodynamic instability, or persist beyond 3 menstrual cycles without resolution.

Endometriomas

"Chocolate cysts" — ovarian cysts containing old, dark blood from ectopic endometrial tissue. They have a characteristic ground-glass echogenicity on ultrasound and are closely associated with endometriosis elsewhere in the pelvis. They are the most clinically significant type of cyst for fertility, progressively destroying surrounding healthy ovarian cortex and reducing ovarian reserve. See the endometriosis treatment article and the dedicated discussion of endometrioma surgery vs IVF decision.

Dermoid Cysts (Mature Teratomas)

Derived from germ cells, dermoid cysts contain elements of all three germ cell layers — hair, teeth, fat, skin. They have a characteristic ultrasound appearance (echogenic material, shadowing from calcification). They grow slowly (typically 1 to 2 mm per year) and are bilateral in approximately 10 to 15% of cases. Most are asymptomatic, but they carry a small risk of torsion (twisting of the ovary around its pedicle) due to their weight. Surgical removal is recommended for dermoids above 5 to 6 cm, those causing symptoms, or those in women planning IVF (to improve ovarian access during egg collection). Dermoid cyst removal requires meticulous surgical technique to avoid spillage of cyst contents, which causes chemical peritonitis.

Cystadenomas

• Serous cystadenomas: Thin-walled, filled with clear watery fluid. Generally benign; can grow very large. Require removal if large (above 5 to 7 cm) or if features raise concern for malignancy.
• Mucinous cystadenomas: Filled with thick, mucus-like fluid. Can grow very large. Generally benign but require surgical removal due to size and the rare association with mucinous borderline tumours.

Borderline Ovarian Tumours

Somewhere between benign cysts and frankly malignant ovarian cancer — borderline tumours have some atypical cells but do not invade surrounding tissue. They require surgical removal and specialist oncology input. They may recur after conservative surgery but rarely cause mortality when treated appropriately. Fertility-sparing surgery (removing the cyst without the ovary) is possible in many cases.

Ovarian Cancer

True ovarian cancer — the most feared diagnosis. Features that raise concern on ultrasound include: solid components, papillary projections, septations with blood flow on Doppler, bilateral cysts, ascites (fluid in the abdomen), and elevated CA-125 or other tumour markers. Any cyst with malignant features requires urgent specialist assessment and should be managed at a gynaecological oncology unit.

The IOTA Classification

The International Ovarian Tumour Analysis (IOTA) group has developed simple rules for ultrasound classification of ovarian cysts that identify features reassuring for benignancy (B-features) or suspicious for malignancy (M-features). Features reassuring for benignancy: unilocular cyst, solid components below 7 mm, acoustic shadows (from calcification, as in dermoids), smooth multilocular cyst below 10 cm, no blood flow. Features suggestive of malignancy: irregular solid tumour, ascites, at least 4 papillary structures, irregular multilocular solid tumour above 10 cm, very strong blood flow.

When Is Surgery Indicated?

• Functional cysts persisting beyond 3 menstrual cycles without resolution
• Endometriomas above 4 cm (particularly before IVF or when causing symptoms)
• Dermoid cysts above 5 to 6 cm or symptomatic
• Cystadenomas above 5 to 7 cm
• Any cyst with malignant features on ultrasound — urgent
• Ovarian torsion — an emergency
• Ruptured cyst with significant intra-abdominal haemorrhage — emergency

Ovarian Cysts and Fertility

Most ovarian cysts do not impair fertility. The key exceptions:

• Endometriomas: Directly damage the surrounding ovarian cortex, progressively reducing AMH and antral follicle count.
• Large cysts of any type: May impair access to follicles at IVF egg collection — both from the affected ovary (which may be occupied by the cyst) and potentially by displacing adjacent structures.
• Cysts arising during IVF stimulation: An unexpected cyst arising during stimulation may require aspiration before egg collection.

Before starting IVF, any persistent ovarian cyst should be assessed and managed appropriately. A baseline scan at the start of the stimulation cycle confirms the ovaries are clear before beginning injections.

Frequently Asked Questions

Q1. I have a 3 cm cyst on my left ovary. My doctor wants to wait and rescan in 3 months. Is this right?

Yes — a 3 cm simple (thin-walled, no solid components, no blood flow) cyst in a premenopausal woman is very likely functional and very likely to resolve. A 3-month rescan to confirm resolution is appropriate management. If the cyst persists beyond two to three menstrual cycles without change, further assessment and possible treatment is warranted.

Q2. Can ovarian cysts turn into cancer?

Functional cysts do not become malignant — they are physiological, not pathological, and resolve spontaneously. Endometriomas carry a very small but real lifetime risk of transformation to endometrioid or clear cell ovarian cancer (approximately 0.3 to 1%). This risk is not zero, which is one reason for surgical removal of large or symptomatic endometriomas. Borderline tumours by definition carry recurrence risk. True primary ovarian cancer typically arises de novo rather than from pre-existing benign cysts.

Q3. I had a cyst removed from my right ovary 2 years ago. I now have one on the same side. Will surgery again reduce my reserve?

Yes — each surgical intervention on an ovary carries some risk of removing healthy ovarian cortex and reducing AMH. This risk increases with each successive operation. Before agreeing to repeat surgery, it is worth getting a current AMH and AFC assessment to understand the reserve remaining, and discussing with a surgeon experienced in fertility-preserving technique whether the risks of further surgery outweigh the benefits in your specific situation. Sometimes, for recurrent endometriomas in older women with already reduced reserve, proceeding directly to IVF is more protective of overall fertility.