BACKGROUND
Rates of thyroid cancer has increased in recent years, especially in young woman. Initial treatment of thyroid cancer is surgery. Some patients may require additional treatment with radioactive iodine therapy to destroy any potentially remaining thyroid cancer cells. As thyroid hormone is very important for normal pregnancy, people have been interested to know potential impact of thyroid cancer treatment on fertility (being able to become pregnant). Previous studies did not show decrease in pregnancy rate in thyroid cancer patients who were treated with radioactive iodine therapy compared to those who did not receive radioactive iodine therapy. However, patients who were treated with radioactive iodine therapy were found to have lower ovarian reserve (an indicator for quality and number of eggs remaining in ovary), compared to those who were not treated with radioactive iodine therapy.

This study aimed to assess potential impact of thyroid cancer treatment on fertility and pregnancy rate in women in Israel.

THE FULL ARTICLE TITLE
Hirsch D et al. 2023 Infertility and pregnancy rates in female thyroid cancer survivors: A retrospective cohort study using health care administrative data from Israel. Thyroid 33:456–463. PMID: 36785948.

SUMMARY OF THE STUDY
A total of 1164 woman with thyroid cancer diagnosed before 40 years of age were identified from the records of one of the largest national insurance companies in Israel. A total of 5030 women without history of thyroid disease matched by age to thyroid cancer patients were selected from the same records as a comparison group (controls). The average age of patients included was 31.6 years, and the average follow-up time was 10 years. Thyroid cancer patients and controls had no significant differences in baseline serum TSH level, number of women with history of prior infertility, or number of prior pregnancies per woman.

Thyroid cancer patients had a higher overall rate of infertility diagnosis (difficulty getting pregnant or inability to get pregnant) compared to those without thyroid disease (23.9% vs. 20.4%). Infertility rate remained higher in thyroid cancer patients compared to controls even after excluding those who had infertility diagnosis before thyroid cancer diagnosis or inclusion in the study (28.7% vs. 24.5%). However, there were no significant differences in pregnancy rates between thyroid cancer patients and controls.

Thyroid cancer patients, on average, were slightly older at time of pregnancy and took longer to become pregnant compared to control patients (33.3 years vs. 32.7 years, and 37 months vs. 31 months, respectively). When patients were divided into four groups based on age (≤26.8, 26.8–31.6, 31.6–35.6, and ≥35.6 years), infertility rate was significantly higher in thyroid cancer patients than controls in those aged 26.8-31.6 years and ≥35.6 years (32.4% vs 24.1% and 15.9% vs 11.5%, respectively).

Among thyroid cancer patients, 52.5% were treated with radioactive iodine therapy after thyroidectomy. After accounting for small age differences, there were no significant differences in infertility rate or pregnancy rate between thyroid cancer patients treated with radioactive iodine therapy and thyroid cancer patients not treated with radioactive iodine therapy. However, average time to pregnancy after thyroid cancer diagnosis was longer in thyroid cancer patients treated with radioactive iodine therapy compared to thyroid cancer patients not treated with radioactive iodine therapy (45 months vs. 29 months).

WHAT ARE THE IMPLICATIONS OF THIS STUDY?
In conclusion, this study found that female Israeli thyroid cancer patients had a higher infertility rate and longer time to pregnancy compared to those without thyroid disease. However, there was no significant impact of radioactive iodine therapy treatment in infertility rate or pregnancy rate in patients with thyroid cancer. It is not entirely clear what factors contribute to the higher infertility rate in thyroid cancer patients compared to patients without thyroid disease. It is, however, reassuring that pregnancy rate between the two groups was not different, suggesting that thyroid cancer diagnosis did not significantly affect the ultimate ability to become pregnant. Therefore, it would be important for patients to be aware of this potential impact of thyroid cancer treatment. We would encourage patients to discuss with their physicians regarding treatment plan after diagnosis of thyroid cancer if they are interested in pregnancy in near future.

— Sun Lee, MD

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