Ovaries are small, almond-shaped organs that produce and release eggs and secrete the sex hormones estrogen and progesterone. Their size is dynamic and changes significantly across a woman’s lifetime. A notable reduction in size occurs as she transitions out of her reproductive years, which is a normal part of the aging process.
Normal Ovarian Size and Function
Throughout the reproductive years, the ovaries are at their largest and most active. The average ovary measures about 3 to 5 centimeters in length, with a volume generally falling within the range of 3 to 10 cubic centimeters (cm³).
Ovarian size is directly influenced by the presence of developing follicles, which are fluid-filled sacs containing the eggs. As part of the monthly cycle, follicles grow substantially, briefly increasing the overall size of the ovary. Beyond egg production, the ovaries also produce the steroid hormones estrogen and progesterone, which regulate the menstrual cycle and maintain secondary sex characteristics.
Age-Related Atrophy and Menopause
Ovarian shrinkage is directly tied to the depletion of the ovarian reserve, the finite supply of follicles a woman is born with. This process, known as follicular depletion, accelerates dramatically in the decade leading up to menopause. When the reserve is nearly exhausted, the ovaries cease producing sufficient estrogen and progesterone, marking the menopausal transition.
Postmenopausal ovaries are significantly smaller due to atrophy, losing the functional tissue that contributed to their size during reproductive years. The average ovarian volume declines to approximately 2.8 cm³ at the time of menopause and continues to decrease thereafter. An ovarian volume of less than 4 cm³ is often considered a strong indicator of postmenopausal status.
The hormonal consequences of follicular loss drive this physical shrinkage. As developing follicles decline, Inhibin B production decreases, causing the pituitary gland to increase its output of Follicle-Stimulating Hormone (FSH). This attempt to stimulate the ovaries eventually becomes ineffective, and estrogen levels drop sharply, resulting in the small, inactive postmenopausal ovary.
Non-Aging Factors Affecting Ovarian Size
While aging is the primary cause of ovarian shrinkage, other factors and medical interventions can accelerate this process or cause temporary size changes.
Medical Treatments
Certain medical treatments, such as chemotherapy and radiation therapy, can prematurely deplete the ovarian reserve, leading to atrophy and early menopause. This damage occurs because the treatments can directly destroy the primordial follicles or affect the surrounding supportive cells.
Hormonal treatments also influence ovarian size. For example, Gonadotropin-Releasing Hormone (GnRH) agonists are used to temporarily suppress ovarian function for medical reasons. These drugs cause a reversible reduction in ovarian volume by inhibiting the pituitary-ovarian axis, which suppresses follicular development.
Hysterectomy
A hysterectomy, the surgical removal of the uterus, can contribute to a reduction in ovarian function and size, even when the ovaries are left intact. The blood supply to the ovaries is partially shared with the uterus. Ligation of the uterine arteries during the procedure can reduce ovarian blood flow by 50% to 70%. This compromise in circulation can accelerate the rate of follicular loss, resulting in a higher risk of earlier ovarian failure.