Ovarian cysts can cause irregular periods, but most don’t. The majority of ovarian cysts are “functional” cysts that form as a normal part of your menstrual cycle, produce no symptoms, and resolve on their own within a few weeks. Whether a cyst disrupts your cycle depends on its type and whether it’s producing excess hormones.
How Functional Cysts Form
Each month, your ovary grows a small fluid-filled sac called a follicle, which releases an egg at ovulation. After the egg is released, the leftover follicle becomes a temporary structure called a corpus luteum, which produces progesterone to prepare the uterine lining for pregnancy. If pregnancy doesn’t happen, progesterone drops, the lining sheds, and your period starts.
A functional cyst forms when something in this process goes slightly off-script. There are two types. A follicular cyst develops when the follicle doesn’t release the egg and instead keeps growing. A corpus luteum cyst forms when the corpus luteum doesn’t shrink down as expected and instead fills with fluid. Both are common, usually harmless, and typically disappear on their own within about eight weeks.
Which Cysts Disrupt Your Cycle
Follicular cysts and corpus luteum cysts affect your period through different hormonal pathways, and they don’t do it equally often.
Follicular cysts can produce excess estrogen because the cells lining the cyst continue making it. That extra estrogen interferes with the normal hormonal signals that trigger ovulation and start a new cycle. The result is typically less frequent periods, meaning your cycle stretches longer than usual. However, menstrual changes from follicular cysts are not common.
Corpus luteum cysts are more likely to cause noticeable cycle changes. These cysts can produce excess progesterone, which is the hormone responsible for maintaining the uterine lining. When progesterone stays elevated longer than it should, your body gets a signal that mimics early pregnancy, delaying the shedding of the lining and pushing your period back. Spotting or bleeding between periods can also occur with some cysts.
PCOS Is a Different Condition
If you’re experiencing persistently irregular periods and an ultrasound shows multiple small cysts on your ovaries, your provider may evaluate you for polycystic ovary syndrome (PCOS). Despite the name, PCOS is not simply “having ovarian cysts.” It’s a hormonal condition diagnosed when at least two of three criteria are present: infrequent or absent ovulation, signs of excess androgens (like acne, excess hair growth, or elevated testosterone), and a specific pattern of many small follicles on ultrasound.
This distinction matters because having polycystic-appearing ovaries on a scan without other clinical features does not mean you have PCOS. Conversely, a diagnosis can be made without a scan at all if the first two criteria are present. PCOS causes chronic cycle irregularity through a fundamentally different mechanism than a single functional cyst. If periods are coming less than once every three months, there’s a risk of the uterine lining building up excessively, which needs medical attention.
How Cysts Are Found and Evaluated
Most functional cysts are discovered incidentally during a pelvic ultrasound done for another reason. When a cyst is found, its appearance on imaging helps determine whether it’s a concern. A thin-walled cyst with smooth, regular borders, a single chamber, and a diameter under 10 cm is almost always benign, with a malignancy rate of 0 to 1 percent regardless of age. Cysts with internal dividers, solid areas, or calcifications get a more thorough workup.
If you’re having irregular periods and a cyst is found, your provider will consider the cyst’s size, type, and hormone-producing potential alongside your symptoms and lab work. A small, simple cyst in someone with irregular periods isn’t automatically the cause. Other factors like stress, thyroid issues, weight changes, and PCOS are often more likely explanations for ongoing cycle disruption.
What Happens Without Treatment
Functional cysts usually resolve on their own. Follicular cysts in younger patients typically disappear within eight weeks. For corpus luteum cysts, observation for about three months is the standard approach when there are no symptoms. Once the cyst shrinks and stops producing excess hormones, your cycle generally returns to its previous pattern without any intervention.
During the time a hormone-producing cyst is present, you might notice one or two cycles that are longer than usual, shorter than usual, or accompanied by spotting. This is a temporary disruption, not a sign of lasting damage to your reproductive system.
When Cysts Need Treatment
Most functional cysts need nothing more than monitoring. Reasons a provider might recommend intervention include a cyst that persists for three months or longer, grows to 6 cm or more, causes pelvic pain, or leads to urinary frequency from pressure on the bladder. Simple cysts between 6 and 12 cm can sometimes be monitored safely rather than removed immediately.
When surgery is needed, the goal is to remove the cyst while preserving as much ovarian tissue as possible. This is typically done through a minimally invasive procedure. Surgical removal is more urgent when there’s concern about ovarian torsion (the ovary twisting on itself), rupture with significant bleeding, or features that suggest something other than a functional cyst.
Preventing Future Cysts
Combined hormonal birth control pills that contain estrogen and progestin can reduce the likelihood of new functional cysts forming by suppressing ovulation. If an egg isn’t released, a follicular cyst can’t form, and no corpus luteum develops afterward. This is why early studies found that women on birth control pills had fewer cysts overall.
It’s worth noting that while birth control pills help prevent new cysts, they don’t speed up the resolution of a cyst that already exists. If you already have a functional cyst, it will need to shrink on its own or be removed. The pills are a preventive measure, not a treatment for an existing cyst. For someone whose irregular periods are being caused by recurrent functional cysts, hormonal contraceptives can stabilize the cycle by preventing the cysts from forming in the first place.