Fertility Q&A

Resumption of menstrual periods does not necessarily indicate fertility.

By Karine Chung, MD, MSCE

If you are undergoing cancer treatment, you may already be aware that cancer therapies—including chemotherapy and radiation—can cause infertility and premature menopause. What you may not know is that resuming regular periods after completing your cancer treatment is not necessarily a sign that your fertility has been unaffected. Although many women will resume regular menstrual periods after treatment, this does not necessarily indicate that they are fertile. In fact, the presence or absence of menstruation is a highly inaccurate assessment of the potential for pregnancy.

Q. What do regular periods indicate?

A. The good news about having menstrual periods is that, if you are menstruating at regular intervals of every 24 to 35 days, you are likely ovulating (releasing a mature egg) each month. The process of ovulation is a complex and tightly controlled sequence of events that is driven by hormonal signals from the hypothalamus and the pituitary gland in the brain. Most women stop having periods during their cancer treatment, possibly due to stress mechanisms that signal the brain that it is not a good time to have a baby. As the acute stress of cancer therapy comes to an end, the hormonal signals can recover and ovulation can resume. Although ovulation is a necessary component of conceiving, it is only the first step in a series of essential events that precede a successful pregnancy.

Q. Infertility despite regular ovulation: how does it happen?

A. After ovulation, additional events that need to occur to achieve pregnancy include fertilization, embryo cell division, and implantation. These are primarily influenced by the egg; and, of a woman’s finite supply of eggs, only a fraction of them are able to accomplish these events with the necessary precision and efficiency—a concept we refer to as “egg quality.”

Women who have not been exposed to cancer therapies experience an accelerated decline in fertility at an average age of 37 due to reduction in the number of eggs and a corresponding loss of high-quality eggs. Within a matter of years, a critical threshold is reached at which the number of eggs and the quality of eggs is too low to result in a successful pregnancy. Thus cessation of fertility occurs at an average age of 41, though menstrual cycles continue to be regular and ovulatory until age 46, on average.

Chemotherapy and radiation to the pelvis can dramatically reduce a woman’s egg supply, with higher doses leading to greater degrees of loss. As a result, many women have a shortened window of time to achieve pregnancy. If the remaining pool of eggs is below the critical threshold following cancer therapy, pregnancy using one’s own eggs is no longer possible regardless of whether menstrual cycles are occurring.

The most reliable way to assess fertility after cancer therapy is through measurement of hormone levels in the blood (follicle-stimulating hormone and estradiol levels timed to specific phases of the menstrual cycle, and anti-Müllerian hormone levels). An ultrasound of the ovaries can also be useful to approximate fertility potential. These tests are best performed and interpreted by reproductive endocrinologists.

Some Final Thoughts

If you are considering having children after completing your cancer treatment, be sure to speak with your oncologist about your fertility questions before your treatment begins. The impact of cancer treatment on a woman’s fertility varies from individual to individual, so it is important to understand the risks that are specific to you. For many women, consulting a fertility specialist and/or undergoing a fertility preservation procedure prior to the initiation of cancer treatment is an excellent choice.