Finding a cyst on an ultrasound during a fertility workup is unsettling, but most ovarian cysts are not the fertility-threatening diagnosis your anxiety might suggest. The critical question is not whether you have a cyst, but what kind it is. Functional cysts and pathological cysts behave entirely differently, and understanding the distinction determines whether treatment is delayed, modified, or unaffected.
Functional Cysts: The Ones That Belong There
Functional cysts are a normal part of the menstrual cycle. They form when the ovulation process does not complete as expected, and they almost always resolve on their own within one to three menstrual cycles.
- Follicular cyst: A follicle grows but does not release the egg. It continues to enlarge (typically 2.5 to 5 cm) and usually resolves within 4 to 8 weeks. These are the most common ovarian cysts in reproductive-age women.
- Corpus luteum cyst: After ovulation, the corpus luteum (the structure that remains after the follicle releases the egg) fills with fluid or blood instead of breaking down normally. These can reach 3 to 8 cm and typically resolve within 1 to 2 cycles. They are often found incidentally during early pregnancy ultrasounds and are normal.
Neither type impairs long-term fertility. However, a functional cyst present at the start of a treatment cycle may cause a delay.
When Functional Cysts Delay Treatment
If a functional cyst is found on a baseline ultrasound (cycle day 2 or 3, before starting medication), your RE may postpone stimulation:
| Cyst Type | Size Threshold | Typical Decision |
|---|---|---|
| Simple follicular cyst | Under 20 to 25 mm | Proceed with treatment (most protocols) |
| Simple follicular cyst | Over 25 mm | Wait one cycle or aspirate |
| Corpus luteum cyst | Any size with elevated estradiol | Wait; CL cysts produce hormones that interfere with stimulation response |
| Estrogen-producing cyst | Any size with estradiol above baseline | Wait; elevated estrogen suppresses response to stimulation medications |
The concern is not the cyst itself, but the hormonal environment it creates. A cyst producing estrogen can interfere with follicle recruitment during stimulation, leading to a suboptimal response. One cycle of oral contraceptive pills (OCPs) is sometimes prescribed to suppress the cyst before restarting.
Pathological Cysts: The Ones That Need Evaluation
Pathological cysts do not arise from normal ovulation. They persist across cycles and may affect fertility directly. The three most common in reproductive-age women:
Endometriomas ("Chocolate Cysts")
Endometriomas form when endometrial tissue grows on or in the ovary, creating a blood-filled cyst. They appear on ultrasound as a homogeneous, ground-glass mass and are associated with endometriosis.
- Impact on fertility: endometriomas can reduce ovarian reserve (lower AMH, lower antral follicle count on the affected ovary), impair egg quality, and create inflammation that affects the pelvic environment
- Surgery (cystectomy) may be recommended for endometriomas larger than 4 cm, but surgery itself can reduce ovarian reserve by removing healthy tissue alongside the cyst wall
- Many REs prefer to proceed directly to IVF with endometriomas present, especially if the patient's AMH is already declining, to avoid further reserve loss from surgery
Dermoid Cysts (Mature Teratomas)
Dermoid cysts are benign tumors that contain tissue from multiple cell types (skin, hair, teeth, fat). They grow slowly and do not affect fertility unless they are large enough to displace ovarian tissue or twist the ovary (torsion).
- Dermoids under 5 cm are typically monitored and do not require intervention before fertility treatment
- Larger dermoids or those causing symptoms (pain, pressure) may require laparoscopic removal (cystectomy) before proceeding
Cystadenomas
Serous and mucinous cystadenomas are benign epithelial tumors. They can grow large (5 to 20+ cm) and do not resolve spontaneously. They do not directly impair fertility but may require surgical removal if they are large, growing, or causing symptoms.
How Cysts Are Distinguished
Ultrasound characteristics (simple vs. complex, thin-walled vs. thick-walled, presence of solid components or internal echoes, blood flow patterns) guide the initial classification. Most functional cysts appear as simple, thin-walled, anechoic (black on ultrasound) structures. Endometriomas have a characteristic "ground glass" appearance. Dermoids show mixed echogenicity. If the classification is uncertain, MRI may be ordered before any surgical decision.
PCOS and Cystic Ovaries
Polycystic ovarian morphology (PCOM), the "string of pearls" appearance on ultrasound where 12 or more small (2 to 9 mm) follicles are visible per ovary, is not a cyst disease. These are small antral follicles that never mature and ovulate, resulting from the hormonal disruption of PCOS. They do not require removal. Treatment targets ovulation induction (letrozole, gonadotropins) rather than cyst management.
When to Push for Action vs. When to Wait
- Wait: Simple functional cysts under 25 mm with normal estradiol. They will likely resolve within one cycle.
- Discuss further: Cysts that persist across two or more cycles, complex-appearing cysts, or cysts associated with elevated CA-125 (a blood marker).
- Act: Endometriomas over 4 cm, large dermoids, any cyst with suspicious features (solid components, irregular walls, increased blood flow), or cysts causing pain or torsion symptoms.
The Endometrioma Dilemma: Surgery vs Proceed
The surgical decision for endometriomas deserves deeper examination because it is one of the most debated topics in reproductive medicine. The dilemma is straightforward: endometriomas impair fertility, but removing them surgically also damages the ovary. The question is which option causes less harm in your specific situation.
Evidence supporting surgery (cystectomy before IVF):
- Endometriomas larger than 4 cm can physically block access to follicles during egg retrieval
- The inflammatory environment created by endometriomas may reduce egg quality in the affected ovary
- Removal reduces the risk of rupture or infection during stimulation
- Some studies show improved IVF outcomes after cystectomy for large endometriomas
Evidence supporting proceeding directly to IVF (no surgery):
- Cystectomy reduces AMH by an average of 30 to 40 percent (the healthy cortex removed with the cyst wall contains primordial follicles)
- In patients with already diminished reserve (AMH below 1.5 ng/mL), the reserve loss from surgery may eliminate the remaining IVF window
- Endometriomas smaller than 4 cm do not typically block retrieval access
- Multiple studies show similar IVF pregnancy rates with endometriomas present vs. after cystectomy
The individualized factors that typically tip the decision: your age, your AMH, the endometrioma's size, whether it is unilateral or bilateral, and whether the endometrioma is causing pain that would complicate stimulation. There is no universal right answer, which is why this is a decision your RE should discuss with you explicitly, citing your specific numbers.
Cyst Aspiration: When and Why
Aspiration (draining a cyst with a needle under ultrasound guidance) is sometimes performed as an alternative to waiting for a functional cyst to resolve. It is a quick, office-based procedure that immediately reduces cyst size and allows the treatment cycle to proceed.
The limitation: functional cysts that are aspirated have a recurrence rate of roughly 30 to 50 percent because the cyst wall remains intact. Aspiration addresses the immediate obstruction but does not prevent the cyst from refilling. For persistent or recurrent cysts, a course of oral contraceptives followed by a fresh baseline assessment is more reliable than repeated aspiration.
Aspiration of endometriomas is generally discouraged because the thick, old blood content tends to reaccumulate rapidly, and there is a theoretical risk of seeding endometrial tissue. When endometriomas need intervention, excision (cystectomy) is the preferred approach.
Torsion: The Emergency to Know About
Ovarian torsion occurs when the ovary twists on its vascular pedicle, cutting off blood supply. Large cysts (greater than 5 cm) increase torsion risk because the added weight makes the ovary more mobile. Torsion is also a risk during IVF stimulation when the ovaries are enlarged.
Symptoms of torsion: sudden, severe, one-sided pelvic pain, often accompanied by nausea and vomiting. The pain may come and go (intermittent torsion) or be constant (complete torsion). This is a surgical emergency. Delayed treatment can result in ovarian loss. If you have a known large cyst and experience sudden severe pelvic pain, go to the emergency room and tell them you have a large ovarian cyst and suspect torsion.