An ovarian cyst is a fluid-filled sac that forms on or inside an ovary. Most are harmless, develop as a normal part of the menstrual cycle, and disappear on their own within a few months. Your body actually creates a small cyst every month during ovulation. The difference comes when a cyst doesn’t go away, grows larger, or looks unusual on imaging.
How Ovarian Cysts Form
The two most common types, functional cysts, are directly tied to your menstrual cycle. About halfway through each cycle, an egg bursts out of a small fluid-filled sac called a follicle. Normally, the follicle breaks open, releases the egg, and shrinks. When something in that process goes slightly off-script, a cyst can form.
A follicular cyst happens when the follicle never ruptures. Instead of releasing the egg, it keeps growing and fills with fluid. A corpus luteum cyst forms after the egg has already been released. The empty follicle is supposed to shrink and produce hormones, but sometimes the opening seals shut, trapping fluid inside. Both types are almost always benign and typically resolve within two to three menstrual cycles without any treatment.
Other Types of Ovarian Cysts
Not all cysts are tied to your monthly cycle. These less common types don’t resolve on their own as predictably and sometimes need closer monitoring or removal.
- Dermoid cysts are the most common type of benign ovarian germ cell tumor. They contain tissue that can include fully formed skin, hair, teeth, nerves, and even brain tissue. Dermoid cysts are likely present from birth but grow slowly, often going undetected until they show up on a routine imaging scan during your reproductive years.
- Cystadenomas develop on the outer surface of the ovary and are filled with watery or mucus-like fluid. They can grow quite large.
- Endometriomas form when tissue similar to the uterine lining grows on the ovaries. Sometimes called “chocolate cysts” because of the dark blood they contain, these are associated with endometriosis and can affect fertility.
Symptoms to Recognize
Most ovarian cysts cause no symptoms at all. They’re often discovered incidentally during a pelvic exam or ultrasound performed for another reason. When a cyst does cause symptoms, you might notice a dull ache or pressure on the side of the affected ovary, bloating, or a feeling of fullness in your lower abdomen. Some cysts cause pain during your period or during sex.
Two complications require urgent medical attention. A ruptured cyst can cause sudden, sharp pain on one side of the pelvis, sometimes with light bleeding. The pain can be intense but usually subsides as the fluid is reabsorbed. Ovarian torsion is rarer and more serious: a large cyst can cause the ovary to twist on itself, cutting off its blood supply. This typically causes sudden, severe pain along with nausea and vomiting, and it needs emergency treatment to save the ovary.
How Cysts Are Diagnosed
A pelvic ultrasound is the primary tool for finding and evaluating ovarian cysts. It shows the cyst’s size, shape, location, and whether it’s filled with fluid, solid tissue, or a mix of both. A simple, thin-walled cyst filled only with fluid is almost always benign. Cysts with solid areas, irregular walls, or internal blood flow get closer scrutiny.
A blood test measuring a protein called CA-125 is sometimes ordered, particularly in postmenopausal women, to help assess whether a cyst could be cancerous. This test isn’t accurate enough to use as a general screening tool because many non-cancerous conditions, including menstruation, endometriosis, uterine fibroids, and even pregnancy, can raise CA-125 levels. It’s most useful as one piece of a larger picture alongside imaging.
When Cysts Need Treatment
Size is one of the main factors guiding the next step. In premenopausal women, simple cysts smaller than 5 cm (about 2 inches) typically resolve within two to three cycles and don’t need any follow-up beyond a routine check. Cysts between 5 and 7 cm are generally monitored with a yearly ultrasound. Cysts larger than 7 cm usually require either advanced imaging or surgical evaluation, and a referral to a gynecologist.
The American College of Obstetricians and Gynecologists notes that simple cysts up to 10 cm can often be safely monitored with repeat imaging rather than surgery, even in postmenopausal patients. For postmenopausal women with a small cyst under 5 cm, a normal CA-125 level, and no concerning features on ultrasound, a follow-up scan in four to six months is a common approach.
When surgery is needed, it’s usually done laparoscopically through small incisions. This approach means shorter recovery and less pain compared to open surgery. If there’s any suspicion the cyst could be cancerous based on imaging or blood work, open surgery is preferred so the surgeon can evaluate the area more thoroughly.
Ovarian Cysts and Fertility
The standard functional cysts, follicular and corpus luteum, do not affect your ability to get pregnant. They form as part of normal ovulation and resolve on their own.
Endometriomas are a different story. These cysts are linked to difficulty conceiving, partly because the underlying endometriosis can damage ovarian tissue and interfere with egg quality. Polycystic ovary syndrome, despite its name, is not simply a matter of having cysts on the ovaries. PCOS is a metabolic condition driven by hormone imbalance and insulin resistance. It can lead to less frequent ovulation, which may contribute to fertility challenges. Some women with PCOS don’t even have visible ovarian cysts at all.
How Common They Are
Ovarian cysts are extremely common across all age groups. Among postmenopausal women screened with transvaginal ultrasound in a large National Cancer Institute trial involving over 15,000 women, simple cysts were visible in 14% of women at their first scan, and new cysts appeared at a rate of 8% per year. Most of these cysts remained stable or resolved by the next annual exam. In premenopausal women, the prevalence is even higher because functional cysts form routinely with every ovulatory cycle. The vast majority are never noticed and never cause problems.