Ovaries are small, oval-shaped organs roughly the size and shape of an almond or a large grape, sitting on either side of the uterus in the lower pelvis. Each one measures about 3 to 5 centimeters long, 1.5 to 3 centimeters wide, and weighs only a few grams. They have a smooth, pinkish-white or pearly surface during the reproductive years, though that surface becomes increasingly pitted and scarred over time as eggs are released month after month.
Size, Shape, and Surface
A healthy ovary in a person of reproductive age is firm and slightly oblong. If you could hold one, it would fit easily between your thumb and forefinger. The outer surface starts out relatively smooth in adolescence, but each ovulation leaves a tiny scar where the egg broke through. By your 30s and 40s, the surface can look more irregular and textured, almost wrinkled, simply from years of normal function.
Several ligaments hold the ovaries in place within the pelvis. The ovarian ligament connects each ovary to the uterus, though the ovary and uterus don’t actually touch. The open, fringed end of each fallopian tube hovers close to the ovary’s surface, ready to catch a released egg.
What’s Inside: Cortex and Medulla
If you sliced an ovary in half, you’d see two distinct layers. The outer layer, called the cortex, looks dense and granular. That grainy texture comes from dozens of tiny follicles, each one a fluid-filled sac containing an immature egg, all sitting at different stages of development. Some are microscopic, while others have grown large enough to see with the naked eye.
The inner layer, the medulla, looks completely different. It’s softer and spongier, made of loose connective tissue packed with blood vessels, lymphatic channels, and nerve fibers. This is essentially the ovary’s supply hub, delivering oxygen and nutrients to the follicles growing in the cortex above it.
How Ovaries Change Throughout the Month
An ovary doesn’t look the same from one week to the next. Its appearance shifts dramatically across the menstrual cycle as follicles grow, an egg is released, and a new temporary structure forms in its place.
In the first week of a cycle, small fluid-filled follicles begin appearing in the cortex, each roughly 2 to 3 millimeters across. Over the next several days, one follicle (occasionally two) pulls ahead and grows rapidly while the others shrink back. By mid-cycle, this dominant follicle can reach 18 to 25 millimeters, large enough to visibly bulge from the ovary’s surface. At this point, the ovary on the dominant side looks noticeably larger and rounder than the other one.
At ovulation, the follicle ruptures and releases the egg. On ultrasound, the most common sign is a sudden disappearance or collapse of the follicle. A small amount of fluid often spills into the surrounding pelvic space, which is visible in about 77% of cases on the day of ovulation.
After ovulation, something remarkable happens at the rupture site. A saffron-yellow mass of cells forms where the follicle once was, sealing the break and growing into a new structure called the corpus luteum. It can range from just under 2 centimeters to 5 centimeters in size. The yellow color comes from fat-soluble pigments in the cells that now produce progesterone. On ultrasound, the corpus luteum appears as a structure with thick, bright walls surrounding a darker center. If pregnancy doesn’t occur, it gradually shrinks and fades over about two weeks, leaving behind a small white scar.
How Ovaries Change With Age
Ovaries look dramatically different at various life stages. In childhood, they’re small, smooth, and mostly inactive, with no visible follicle development. During the reproductive years (roughly ages 15 to 45), they’re at their largest, plump with follicles and showing a more textured surface.
After menopause, ovaries shrink significantly. They can lose more than half their volume, becoming small, pale, and firm with a wrinkled surface. The follicles that once gave the cortex its granular appearance are gone. What remains is mostly fibrous tissue. On ultrasound, postmenopausal ovaries can be difficult to locate because they’re so much smaller and lack the fluid-filled follicles that make younger ovaries easy to spot.
What a Polycystic Ovary Looks Like
In polycystic ovary syndrome (PCOS), the ovaries have a distinctly different appearance. Instead of one dominant follicle maturing each cycle, many small follicles stall at an early stage and accumulate along the outer edge of the ovary. On ultrasound, this creates a characteristic “string of pearls” pattern: a ring of tiny dark circles, each 2 to 9 millimeters in diameter, lining the cortex.
The diagnostic threshold is 12 or more of these small follicles in a single ovary, or an ovarian volume of 10 milliliters or greater (roughly double the typical size). Some newer guidelines set the follicle count even higher, at 25 or more per ovary, to account for improvements in ultrasound technology that now detect follicles that older machines would have missed. A polycystic ovary is often visibly enlarged and rounder than a typical ovary, though having polycystic-appearing ovaries on imaging alone doesn’t necessarily mean you have PCOS. The diagnosis requires additional criteria like irregular periods or elevated androgen levels.
What Ovaries Look Like on Ultrasound
Most people will never see their ovaries directly, but many will see them on a transvaginal ultrasound. On the screen, a normal ovary appears as a small, oval gray structure with darker (black) circles scattered through it. Those dark circles are the fluid-filled follicles. The surrounding ovarian tissue appears in varying shades of gray.
A dominant follicle mid-cycle shows up as a single large dark circle, sometimes nearly filling the ovary. The corpus luteum after ovulation looks different: a ring of bright tissue with a darker or mixed-texture center, sometimes with internal echoes from a small amount of bleeding at the rupture site. Your doctor may point these structures out during a scan to confirm ovulation or check ovarian health, and knowing what to expect can make the image on the screen much easier to understand.