Thyroid Nodules and Thyroid Cancer in Pregnancy

Thyroid Nodules Are More Likely to Increase in Size During Pregnancy

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Pregnancy can affect thyroid nodules, which are swellings or lumps in the thyroid gland, and can be a solid mass, or a liquid-filled cyst. Most thyroid nodules are benign, but a small percentage can be cancerous.

Thyroid Nodules

According to the 2011 "Guidelines of the American Thyroid Association for the Diagnosis and Management of Thyroid Disease During Pregnancy and Postpartum," nodules are more common after multiple pregnancies, and thyroid nodules are more likely to increase in size during pregnancy. When nodules are discovered during pregnancy, it is recommended that the woman be asked about her family history of benign or malignant thyroid disease and endocrine disorders, previous disease or treatment involving the neck (in particular, any radiation treatments to the head or neck during childhood), as well as when the nodule was detected, and how quickly it is growing.

The Guidelines recommend that all women with a thyroid nodule have TSH and Free T4 measured. If a woman has a family history of medullary thyroid carcinoma or multiple endocrine neoplasia (MEN) 2, calcitonin levels should also be measured.

According to the Guidelines, ultrasound is recommended to determine the features of the nodule, and monitor their growth. If a nodule is less than 10mm in size, a fine-needle aspiration (FNA) biopsy of the thyroid is not required unless there are suspicious characteristics.

If a nodule is growing, or if there is persistent cough or vocal problems, or any other suspicious indicators from the history, the Guidelines recommend an FNA be performed. FNA is considered safe during pregnancy.

The use of radionuclide scanning of the nodule – which is routine for suspicious nodules outside of pregnancy – is contraindicated during pregnancy, due to concerns regarding radiation exposure to the fetus. According to the Guidelines, several research studies have shown, however, that inadvertent use of RAI prior to 12 weeks of gestation did not appear to damage the fetal thyroid.

For benign thyroid nodules, the Guidelines suggest no treatment. If the nodules show rapid growth, changes suspicious of cancer, a repeat FNA should be performed. If nodules are compressing the trachea or esophagus, thyroid surgery can be considered.

Thyroid Cancer

If thyroid cancer is found, the type of thyroid cancer determines the treatment. For well-differentiated thyroid cancer found during pregnancy, the Guidelines suggest that surgery may be generally deferred until after delivery.

For medullary thyroid cancer, surgery is recommended during pregnancy if there is a large primary tumor, or extensive spread to the lymph nodes.

The impact of thyroidectomy during pregnancy has been studied, and generally, if the thyroid surgery is performed during the second trimester, it has not been associated with increased maternal or fetal risk.

The Guidelines recommend that if surgery for well-differentiated thyroid cancer is being deferred until after delivery, an ultrasound should be performed during each trimester to watch for rapid tumor growth. When there is rapid growth, or there is spread to the lymph nodes, surgery is recommended.

In a woman with well-differentiated thyroid cancer who is deferring surgery until after delivery, levothyroxine treatment can be used, with a goal of suppressing TSH level to 0.1-1.5mIU/L.

Treating Hypothyroidism in Pregnant Thyroid Cancer Survivors

According to the Guidelines, in women who have persistent thyroid cancer, TSH can be maintained below 0.1 mIU/L during pregnancy. In women who are free of thyroid cancer but who had a high risk tumor in the past, suppression should be maintained at TSH levels between 0.1 mIU/L and 0.5 mIU/L. In low-risk patients with no signs of thyroid cancer, TSH can be kept at the lower end of the normal range (0.3-1.5 mU/L).

Typically, pregnant women who are on thyroid hormone replacement after thyroid cancer require a smaller dose increase compared to women who are hypothyroid due to other disorders. The Guidelines recommend that in these women, TSH be monitored every 4 weeks during pregnancy, until 16 to 20 weeks of gestation, and again at least once between 26 and 32 weeks of gestation.

RAI Treatment for Cancer and the Effect on Subsequent Pregnancy

Researchers have not found an increase in infertility, miscarriage, stillbirth, neonatal mortality, congenital malformations, preterm birth, low birth weight, or death during the first year of life after radioactive iodine (RAI) treatment for thyroid cancer. There is, however, an increased risk of miscarriage in the months following RAI that can result from insufficient control of thyroid hormones. The Guidelines recommend waiting at least six months after RAI to ensure optimal thyroid management prior to conception.

Pregnancy does not appear to increase the risk for thyroid cancer recurrence in women who have no disease present prior to pregnancy. In women who have any remnant of thyroid cancer, either in terms of visible thyroid tissues, or elevated thyroglobulin (Tg) levels, pregnancy may stimulate thyroid cancer growth.

If a woman has had a previously treated differentiated thyroid cancer, and undetectable thyroglobulin (Tg) levels, no special monitoring is needed during pregnancy. However, the Guidelines recommend an ultrasound during each trimester in a woman previously treated for differentiated thyroid cancer who has high Tg levels or any evidence of persistent disease.

View Article Sources
  • Stagnaro-Green, Alex, et. al. "Guidelines of the American Thyroid Association for the Diagnosis and Management of Thyroid Disease During Pregnancy and Postpartum." Thyroid. Volume 21, Number 10, 2011 (Online)