Will Having Thyroid Cancer Affect My Ability to Have Children?

By Mara Roth, MD

The diagnosis of thyroid cancer has become much more common over the last few decades among people of all ages, genders, races and ethnicities. This diagnosis can affect both women and men, who are often at a point in their lives when they are planning to have children. Being diagnosed with thyroid cancer, and undergoing the treatments necessary, often raises questions regarding whether it is safe to try conceiving, or when/can conception even occur.

For most individuals, thyroid cancer is initially treated with surgery and then sometimes followed by additional treatment with radioactive iodine; however, nearly all individuals will require lifelong thyroid hormone medication after their thyroid cancer treatment.

The diagnosis and treatment of thyroid cancer raises many questions about family planning, especially as treatment progresses. Some of the questions that physicians hear include: Will thyroid cancer affect my ability to have a baby? Will the thyroid hormone medication change the risk of complications in pregnancy? Is it safe to get pregnant after treatment with radioactive iodine? Will my child or children be at increased risk for thyroid cancer?

Here’s what we know: While thyroid hormone is a key hormone in supporting one’s ability to conceive and to carry a pregnancy to delivery, many women who require thyroid hormone for non-cancerous indications still have normal, healthy babies. Thyroid hormone is a safe medication to take during pregnancy, with no risk of birth defects. However, thyroid hormone doses typically need to increase during pregnancy, so if you are taking thyroid hormone medication for any reason, it’s imperative that you have frequent monitoring (usually blood tests) to make sure you have enough thyroid hormone in your body to support the growing baby.

If you’ve been diagnosed with thyroid cancer, you are often put on doses of thyroid hormone medication that are called “suppressive,” meaning that blood levels may be targeted to a hyperthyroid (higher than normal) level to help decrease the risk of thyroid cancer recurrence. During the first trimester of pregnancy, relatively high levels of thyroid hormone are considered normal and mildly increased levels of thyroid hormone are well tolerated. In order to make sure that your levels are in an acceptable range, you should discuss your plans for pregnancy with your endocrinologist so your thyroid dose can be adjusted before attempting to conceive.

Many patients diagnosed with thyroid cancer will require treatment with radioactive iodine (RAI) after surgery. However, this treatment is not safe for pregnant women and, thus, must be delayed if a woman is found to be pregnant before RAI treatment. After treatment with radioactive iodine, both men and women may experience short-term changes in being able to conceive. Several studies have shown a decrease in men’s sperm concentration and sperm quality in the first three to six months after receiving radioactive iodine, which for some may persist for up to a year after treatment. While sperm banking is not generally recommended since the majority of men recover normal testicular function, patients receiving large total doses of radioactive iodine and who wish to have additional children may benefit from a semen evaluation and possibly sperm banking prior to repeated treatment.

Women, too, have a short-term decrease in fertility in the first three to six months after RAI treatment and often have irregular menstrual bleeding during that time period. For some women, irregular periods may last up to a year after treatment. Women receiving RAI therapy are strongly encouraged to avoid pregnancy for at least six months and, ideally, one year after treatment.

Multiple studies have shown no long-term effects on the outcomes of pregnancy in women who have received RAI therapy, except for a slight increase in the risk of miscarriage in those who get pregnant in the first year after treatment. However, as more women delay pregnancy until their mid-to-late 30s, the timing for radioactive iodine therapy may become challenging for women who are also trying to conceive.

The good news is that radioactive iodine is no longer recommended for everyone diagnosed with thyroid cancer. Currently the iodine treatment is considered optional for what is referred to as “low-risk” thyroid cancer. Discuss with your thyroid cancer specialist whether you are considered to be in this category and what this means for your treatment needs and ongoing follow-up. Be proactive with your medical team and ask questions.And make sure your concerns about family planning are answered when discussing the need for and timing of radioactive iodine. It is important to note that nursing women should not receive radioactive iodine, as iodine is concentrated in breast milk.

Pregnancy is a time of increased stimulation to the thyroid gland, and women with normal thyroid glands will increase thyroid hormone production during pregnancy. Due to this increased activity in the gland, many small thyroid nodules will increase in size and thyroid cancers can actually be diagnosed in pregnancy. Since most thyroid cancers tend to have a very good prognosis and tend to be very slow-growing, the 2015 American Thyroid Association guidelines recommend most individuals wait until after delivery to have their thyroid surgery. Each patient and case is unique, so you should discuss the timing of your recommended surgery with your physicians. But the risk of thyroid cancer survival and recurrence is no different between women diagnosed while pregnant versus non-pregnant.

Lastly, many patients worry about the possibility of transmitting the risk of thyroid cancer to their children. Treatment with radioactive iodine will not increase the risk of future children having thyroid cancer. While the most common types of thyroid cancer, papillary and follicular thyroid cancer, are not generally thought to be inherited, there are some families that may have a thyroid cancer genetic link. Specific gene mutations have not yet been identified for papillary thyroid cancer, but there is ongoing research in this area in families where multiple first-degree relatives have all been affected.

For the majority of men and women with thyroid cancer, there is no expected increased risk of thyroid cancer in their children and no recommendation to screen patients’ children for thyroid cancer. There are some rare exceptions with recommendations to screen families, such as in a condition called multiple endocrine neoplasia, where there is a risk of multiple hormone-producing glands being at risk of tumors and cancers, including an uncommon type of thyroid cancer known as medullary thyroid cancer. But these are rare conditions.

Thyroid cancer continues to increase in incidence, particularly in men and women of reproductive age who are thinking about starting families. While both survival and reproductive outcomes are quite good overall, questions concerning pregnancy and family planning should be discussed as part of ongoing treatment and surveillance. Be open about your circumstances and work with your thyroid cancer team to achieve the best outcome for yourself.

Dr. Mara Roth is an Assistant Professor of Medicine at the University of Washington, Seattle, WA, and is board certified in endocrinology, diabetes and metabolism. Dr. Roth co-directs the Endocrine Neoplasia Clinic at the Seattle Cancer Care Alliance and focuses on the diagnosis and management of endocrine tumors, including thyroid, adrenal and parathyroid tumors. She is actively involved in teaching medical trainees, from students to practitioners, and her research focuses on improving diagnosis and treatment of thyroid tumors.