What is normal female fertility, and how is it affected by cancer treatment?

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A woman's ovary contains many thousands of follicles. Each follicle contains a single egg.

During each menstrual cycle, a few immature follicles begin to grow but only one goes on to mature and release its egg. Only one egg is released from the ovary each month in a process called ovulation. After the egg leaves the ovary, it is swept up into the fallopian tube where it can be fertilized by sperm.

The ovary contains a fixed number of follicles at birth. This is called the ovarian reserve. During a woman's lifetime, no new follicles are formed.

The number of follicles in the ovarian reserve declines naturally with age, decreasing sharply around age 37 until menopause around age 50. While age is one way to gauge a woman's fertility, it's actually based on the number of follicles left in her ovarian reserve.

Cancer treatments like chemotherapy and radiation can destroy the follicles in the ovary, which speeds up the natural decline of the ovarian reserve. This can cause temporary or even early menopause.

Chemotherapy uses drugs that target rapidly-growing cells, like cancer cells. But these drugs can also damage healthy tissues. Because follicles grow rapidly in the ovary, they are very sensitive to chemotherapy.

Some chemotherapy only affects mature follicles and the eggs inside them. This means that a woman could lose her menstrual cycle during treatment, but because she still has immature follicles left in her ovarian reserve, she may start having her period again once treatment is over.
However, other kinds of chemotherapy, especially alkylating agents, can also damage the immature follicles in the ovarian reserve. These therapies can cause early menopause even in young women and girls.

Radiation therapy can also affect a woman's fertility, depending on which part of her body is treated. Radiation to the abdomen or reproductive organs can damage follicles in the ovarian reserve and can also damage the uterus, affecting the ability to carry a healthy pregnancy. Radiation to hormone-producing areas of the brain may also impact fertility by blocking normal hormone production.

Not all cancer treatments impact fertility the same way for all women. It is important to talk with a doctor to determine which cancer treatments are available and to understand how those treatments might affect a woman's fertility.