History of thyroid cancer not linked to reduced pregnancy rate for women
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Women who were diagnosed with thyroid cancer as adolescents or young adults have no difference in pregnancy rates compared with those who have never had thyroid cancer, according to a study published in Thyroid.
“Our report provides reassuring evidence of a comparable chance to conceive between female adolescent and young adult patients with thyroid cancer and healthy age-matched controls,” Dania Hirsch, MD, of the Endocrine Institute at Rabin Medical Center in Petah-Tikva, Israel, and colleagues wrote. “However, the findings of a higher rate of infertility, and a longer time to pregnancy in thyroid cancer survivors highlight the need for tailored management and fertility counseling.”
Researchers conducted a retrospective cohort study of women diagnosed with thyroid cancer prior to age 40 years between January 2000 and January 2020. Women had to be aged 25 years or older at the time of data collection to be included. Data were obtained from the Clalit Health Services database in Israel. Women with thyroid cancer were age- and sex-matched, 1:4, with a control group with no documentation of a thyroid abnormality or thyroid medication use and at least one normal thyroid-stimulating hormone measurement. Date of thyroid cancer diagnosis, serum TSH level at diagnosis, purchase of levothyroxine and dates of radioactive iodine therapy were collected from medical records. Infertility was identified as any diagnosis of infertility plus the purchase of infertility medication. Pregnancies were confirmed through an obstetric ultrasound, a pregnancy oral glucose tolerance test, and delivery at a Clalit Health Services hospital.
The cohort included 1,164 women who previously had thyroid cancer (median age at diagnosis, 31.6 years) and 5,030 controls. Of the thyroid cancer group, 68.6% received levothyroxine treatment after diagnosis. A minimal TSH level of less than 0.5 mIU/L was observed in 79.4% of the cancer group. All controls had repeat TSH levels in the normal range.
A higher percentage of women with thyroid cancer were diagnosed with infertility compared with the control group (23.9% vs. 20.4%; P = .008). The findings were similar when the cancer group included only women receiving levothyroxine and when women previously diagnosed with infertility were excluded.
No difference was observed between the groups for pregnancy rate. Time to first pregnancy after cancer diagnosis was longer for the cancer group compared with time to first pregnancy from referent date for the control group (P < .001).
The overall findings for infertility and pregnancy rates were similar when only women with no prior pregnancy were included. When the cohort was divided into quartiles by age, infertility was significantly higher among the thyroid cancer group for women aged 26.8 to 31.6 years and those older than 35.7 years compared with controls, whereas no difference was observed for other age groups. There was no difference in pregnancy rate for any age group.
Radioactive iodine treatment was administered to 52.5% of women with thyroid cancer. There was no difference in infertility or pregnancy rates for women treated with radioactive iodine compared with controls. Women who received multiple radioactive iodine treatments had a longer time to first post-diagnosis pregnancy than controls (47 months vs. 29 months; P = .002).
“Although the thyroid cancer patients were more likely to be diagnosed with infertility and to use infertility therapies than healthy matched controls, the overall pregnancy rate was comparable between the two groups,” the researchers wrote. “Radioactive iodine treatment, whether given once or repeatedly, was not significantly associated with fertility or pregnancy outcomes.”
Perspective
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In this study, Hirsch and colleagues conducted a retrospective cohort study including 1,164 patients with thyroid cancer compared to 5,030 controls followed for a median period of 10 years. The results of the study found that the infertility rate was higher in the thyroid cancer group compared to the control group (23.9% versus 20.4%, P = .008) yet the pregnancy rates were comparable (46.9% vs. 47.7%, P = .625). The median time to first pregnancy post-diagnosis was longer in the thyroid cancer patients than in the controls (37 vs. 31 months, P < .001). There was no difference in infertility and pregnancy rates between patients who received radioactive iodine ablation compared to those who did not, but time to first post-diagnosis pregnancy was longer (median 45 vs. 28 months, P = .02).
The results of this study stress the importance of preconception counseling for patients with thyroid cancer. This is especially true for patients who are older and for those who do not have access to fertility treatments. In this study, no difference in rate of pregnancy was seen, but all patients in the study had access to fertility treatment. In the U.S., fertility treatment is very costly and generally not covered by insurance. Therefore, the increased rate of infertility in patients with thyroid cancer described is concerning. While the study is not able to comment on the etiology of this association, patients need to be informed of the impact thyroid cancer and its treatment may have on their fertility and plans for pregnancy.
The study did not find that treatment with radioactive iodine ablation, including multiple treatments of radioactive iodine ablation, influenced infertility rates. This may be somewhat reassuring for patients. Nevertheless, time to first pregnancy post-diagnosis in patients with thyroid cancer was significantly longer and longer in those treated with radioactive iodine ablation. This is particularly noteworthy as the Census Bureau and National Center for Health Statistics data show that from 1990 to 2019, fertility rates increased by 67% in women ages 35 to 39 years and that for the first time, the median age of first-time mothers is 30 years. By including preconception counseling for patients as part of our treatment plan for patients with thyroid cancer, physicians can help patients with their expectations for pregnancy and plan accordingly.
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