An ovary is a small, oval-shaped gland that produces eggs and hormones. You have two of them, one on each side of your uterus in your lower abdomen. Together, they drive your menstrual cycle, make pregnancy possible, and produce hormones that affect everything from your bones to your mood.
Size, Shape, and Location
Each ovary sits a short distance from the uterus, held in place by a ligament that connects the two without them actually touching. In a person of reproductive age, an ovary is roughly the size of a large grape or small kiwi, averaging about 4 centimeters long. Before menopause, ovaries can reach up to 6 centimeters. After menopause, they shrink considerably, sometimes down to 2 centimeters, closer to the size of a kidney bean.
How Ovaries Produce Eggs
You’re born with all the eggs you’ll ever have. At birth, your ovaries contain roughly 2 million immature eggs. By adolescence, that number drops to about 400,000, and it continues declining throughout your life. Of those hundreds of thousands, only about 400 to 500 will fully mature and be released during your reproductive years.
Each egg lives inside a tiny fluid-filled sac called a follicle. The journey from a resting follicle to one that’s ready for ovulation takes more than 120 days, though most of that process happens quietly in the background. During each menstrual cycle, a brain hormone called FSH (follicle-stimulating hormone) signals a group of follicles to start growing between roughly days 6 and 14 of the cycle. Usually, only one follicle becomes dominant. Around day 14, a surge of another brain hormone called LH (luteinizing hormone) causes that mature follicle to burst open and release its egg. That moment is ovulation.
Hormones the Ovaries Produce
Ovaries are not just egg storage. They are hormone-producing glands, and the hormones they release have wide-reaching effects throughout the body.
Estrogen is produced primarily by cells inside the developing follicle. It’s the hormone most responsible for the physical changes of puberty, and it continues to regulate your menstrual cycle, support bone density, and influence cholesterol levels throughout your reproductive years. Progesterone comes mainly from the corpus luteum, a temporary structure that forms from the leftover follicle after ovulation. Progesterone prepares the uterine lining for a potential pregnancy. If no pregnancy occurs, progesterone levels drop, the lining sheds, and your period begins. The ovaries also produce small amounts of androgens, which play a role in sex drive and energy levels.
The Monthly Ovarian Cycle
The ovarian cycle has two main phases, each driven by a different hormonal signal from the brain.
During the follicular phase (roughly the first half of your cycle), rising FSH levels push follicles to grow. As the dominant follicle matures, it pumps out increasing amounts of estrogen. That rising estrogen eventually triggers the brain to release a burst of LH, which causes ovulation.
The luteal phase follows ovulation. The emptied follicle transforms into the corpus luteum and begins producing progesterone. This progesterone blocks further FSH release and thickens the uterine lining. If a fertilized egg doesn’t implant, the corpus luteum breaks down after about two weeks. Progesterone drops, FSH starts climbing again, and the whole cycle resets.
Fertility and Aging
Because you can’t produce new eggs, your ovarian reserve (the number of remaining eggs) declines steadily with age. This decline isn’t just about quantity. Egg quality also drops over time, meaning eggs are more likely to have chromosomal abnormalities. Fertility starts to decrease gradually in the early 30s and more noticeably after 35. By the time menopause arrives, typically between ages 45 and 55, the ovaries stop releasing eggs altogether and dramatically reduce their hormone production. Bones lose a key source of estrogen protection, which is one reason osteoporosis risk rises after menopause.
Ovarian Cysts
Ovarian cysts are fluid-filled sacs that develop on or inside an ovary. They’re extremely common, and most are harmless.
- Functional cysts are the most common type. They form as a normal part of the menstrual cycle when a follicle doesn’t release its egg or doesn’t shrink after ovulation. They usually cause no symptoms and resolve on their own within 6 to 8 weeks.
- Endometriomas develop when tissue similar to the uterine lining grows on the ovary, often as part of endometriosis. These can cause pain and affect fertility.
- Teratomas (also called dermoid cysts) contain a surprising mix of tissue types, including skin, hair, and sometimes teeth. They can be present from birth and grow during the reproductive years. They’re almost always benign.
- Cystadenomas are benign tumors that form on the outer surface of the ovary. They can grow quite large but are typically not cancerous.
Most cysts are found incidentally during an ultrasound for something else. Larger cysts or those causing pain, pressure, or irregular periods may need monitoring or removal.
Polycystic Ovary Syndrome (PCOS)
PCOS is one of the most common hormonal conditions affecting the ovaries, and it involves more than just cysts. The name is somewhat misleading: the “cysts” seen on ultrasound are actually many small, immature follicles that never developed enough to release an egg. PCOS typically involves irregular or absent periods, elevated androgen levels (which can cause acne or excess hair growth), and those characteristic follicle clusters on imaging. Diagnosis can be tricky during adolescence because some features overlap with normal puberty. PCOS also carries long-term health implications beyond fertility. It’s now considered a risk-enhancing factor for cardiovascular disease, with growing evidence linking it to increased risk of heart attack and stroke even during reproductive years.
Ovarian Cancer
Ovarian cancer is relatively uncommon compared to other cancers, but it’s often caught late because early symptoms are vague: bloating, pelvic discomfort, feeling full quickly, and changes in urination. There’s currently no reliable routine screening test for it.
When ovarian cancer is caught early and still confined to the ovary, the 5-year survival rate is about 92%. The problem is that only 22% of cases are diagnosed at that stage. More than half of cases (54%) are not found until the cancer has already spread to distant sites, where the 5-year survival drops to around 31%. This gap is why paying attention to persistent, unexplained symptoms matters, even when those symptoms seem minor.
What Happens to Ovaries at Menopause
As you approach menopause, the ovaries gradually produce less estrogen and progesterone. This transition period, called perimenopause, can last several years and brings symptoms like irregular periods, hot flashes, sleep disruption, and mood changes. Once you’ve gone 12 consecutive months without a period, you’ve reached menopause. At that point, the ovaries have stopped releasing eggs and their hormone output has dropped significantly. The ovaries don’t disappear, though. They physically shrink and continue producing very small amounts of hormones, particularly androgens, for years afterward.