How Does Thyroid Cancer Affect Pregnancy?

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Thyroid cancer most often occurs in women of reproductive age, making the overlap of pregnancy and thyroid cancer a concern. 

Pregnancy poses unique challenges in managing thyroid cancer, and treatment decisions must consider the well-being of both the mother and the developing baby. 

What Does Your Thyroid Do?

Your thyroid is a butterfly-shaped gland in your neck that produces hormones to regulate your digestive function and metabolism. Because your body is dependent on digestion and metabolism for energy, disorders that affect the thyroid can have wide-ranging effects. 

Symptoms are not usually noticeable at the early stages of thyroid cancer, but as it grows you may be able to detect one or more lumps in your neck, changes in your voice, pain in the neck or throat, difficulty swallowing, and swollen lymph nodes in your neck. 

How Is The Thyroid Affected By Pregnancy?

When you are pregnant, your body and your developing fetus are even more reliant on your thyroid hormones than before. 

Up until the 2nd trimester of pregnancy, the foetus does not produce their own thyroid hormones and is reliant on the mother to supply them. Thyroid hormones are essential for brain development, so a lack of thyroid hormones during pregnancy can have lasting effects on you and your child. 

If you have a known thyroid condition, thyroid hormone levels may need to be monitored during pregnancy. This is because maternal hypothyroidism is a common pregnancy complication, increasing the risk of miscarriage, preeclampsia, neurological and congenital impairment, and abnormal foetal growth.

Thyroid nodules (lesions) can occur during pregnancy, or increase in size and number if they were previously present. This is likely due to the usual thyroid changes during this time, and they generally return to pre-pregnancy size by a few months postpartum.

Should a thyroid nodule be found during a physical exam, and your doctor is concerne,d you could require further assessment. A thyroid ultrasound may be done, and a fine needle aspiration biopsy can be used to confirm thyroid cancer (this procedure is deemed safe during pregnancy).

What Is Thyroid Cancer? 

Thyroid cancer is the abnormal growth of cells in the thyroid. It occurs when DNA changes in the thyroid cells cause them to grow uncontrollably, building up to form a lump or tumour that can invade nearby tissues and even spread to other parts of the body. While thyroid cancer is relatively rare, it is the most common endocrine cancer

There are several types of thyroid cancer. Each type has its own characteristics, prognosis, and recommended treatment approaches. The main types include:

  • Papillary thyroid cancer (the most common)
  • Follicular thyroid cancer
  • Medullary thyroid cancer
  • Anaplastic thyroid cancer
  • Poorly differentiated thyroid cancer

What Are The Concerns Around Thyroid Cancer And Pregnancy?

The two most commonly diagnosed cancers during pregnancy are breast and thyroid cancers. Around 10% of thyroid cancers are diagnosed during pregnancy or in the postpartum period. 

Pregnancy does not affect the prognosis of your thyroid cancer. The cancer will likely progress as it would have. If the disease is aggressive it may continue to be so during pregnancy, demanding more urgent treatment measures.

How Is Thyroid Cancer Treated During Pregnancy?

If your cancer is at an early stage (if the lumps are small), you may not need treatment intervention. However, monitoring via blood tests, physical exams, and imaging would be required. 

If the cancer has progressed, the main treatment is often surgery in the form of a total or partial thyroidectomy (removal of the thyroid), which will likely result in needing to take a thyroid hormone replacement. 

Other treatment options include thyroid hormone therapy, alcohol ablation, radioactive iodine, targeted drug therapy, external radiation, and chemotherapy. Appropriate treatment options will be based on the type and stage of your cancer.

If you are pregnant and you have had your thyroid removed, radioactive iodine treatment is not an option. Radioactive iodine treatment is a common treatment option for thyroid cancer, often administered post-surgery as adjuvant therapy, but it needs to be delayed until after delivery and breastfeeding to ensure the safety of the baby. Exposure to radioactive iodine during pregnancy can lead to foetal hypothyroidism and cognitive disorders. 

If you undergo radioactive iodine treatment for your thyroid cancer before becoming pregnant, it is advised that you avoid pregnancy for 6-12 months after treatment to avoid a negative effect, and preferably to be in remission before undertaking the pregnancy journey. 

In some cases LT4 treatment (which both suppresses the spread of cancer and substitutes thyroid hormone) may be recommended if you are pregnant and need to delay your thyroid cancer treatment. If you have previously had a thyroidectomy you may already be on the treatment, which you will need to remain on and be monitored closely as maternal hypothyroidism can affect foetal development.

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