The ovaries are a pair of small reproductive organs located deep within the female pelvis. Their primary biological role involves producing reproductive hormones, specifically estrogen and progesterone, and releasing eggs for potential fertilization. Because these organs are situated internally, their structure and health are most commonly evaluated using non-invasive medical imaging, specifically ultrasound. The appearance of a healthy ovary is defined by its shape, size, location, and the dynamic changes it undergoes throughout the menstrual cycle.
The Standard Appearance of Healthy Ovaries
On an ultrasound image, a healthy ovary is typically described as an ovoid or almond-shaped structure. It is usually visualized adjacent to the uterus, appearing relatively uniform (homogeneous) compared to the surrounding pelvic tissue.
The internal texture, or echotexture, provides important information about its function. A functioning ovary in a woman of reproductive age often has a speckled or mottled appearance. This texture results from numerous tiny, fluid-filled sacs called follicles, which represent developing eggs. These small follicles appear as anechoic (black) circles scattered mainly within the outer layer, known as the ovarian cortex. The inner section, the medulla, tends to have a slightly brighter appearance due to its composition of connective tissue, blood vessels, and nerves.
Standard Measurements and Location
The healthy ovary’s size falls within a predictable range. In premenopausal women, a typical ovary measures approximately 3 to 5 centimeters in length, 1.5 to 3 centimeters in width, and 0.6 to 1.5 centimeters in thickness. These dimensions correspond to an average ovarian volume generally ranging between 3 and 6 cubic centimeters.
The ovaries are situated on the pelvic sidewalls, near the uterus, often resting within a small depression called the ovarian fossa. They are highly mobile organs, and their exact position can vary significantly, especially in women who have had children. Ultrasound operators often locate the ovaries by first identifying the nearby internal iliac blood vessels, which serve as reliable anatomical landmarks. After menopause, the ovaries naturally shrink due to the cessation of follicular development, making them smaller and sometimes difficult to locate.
Dynamic Changes Throughout the Menstrual Cycle
A defining characteristic of a healthy ovary is its constantly changing appearance in response to monthly hormonal fluctuations. During the follicular phase, which starts on the first day of the menstrual cycle, several small follicles begin to develop, appearing on ultrasound as multiple small, black cysts measuring between 2 and 9 millimeters.
One of these developing structures is selected to become the dominant follicle, growing significantly larger than the others. This dominant follicle can reach an average diameter of 18 to 24 millimeters just before ovulation occurs.
After the egg is released, the collapsed follicle transforms into a temporary structure called the corpus luteum, which produces progesterone. On ultrasound, the corpus luteum has a distinct look, often appearing as a thick-walled, cystic structure with irregular internal margins. It can sometimes contain internal echoes, suggesting the presence of blood products from the recent ovulation. If pregnancy does not occur, the corpus luteum degenerates, and the ovary returns to an appearance dominated by small, non-dominant follicles.
Common Variations That Are Still Healthy
Some findings on an ovarian ultrasound are considered entirely normal and temporary. The most common of these are simple physiological cysts, which result directly from the normal menstrual cycle. These include follicular cysts (dominant follicles that failed to rupture) and corpus luteum cysts.
These benign structures are typically thin-walled, filled with clear fluid, and usually resolve without intervention within a few weeks or months. It is also common for younger women to have multiple small follicles visible in the ovarian cortex, sometimes described as a “string of pearls” appearance. This finding, while a factor in diagnosing certain conditions, is considered a normal variant in individuals who are otherwise ovulating regularly and do not have other symptoms.