Thyroid profile

Thyroid diseases can significantly hamper pregnancy in women. TSH, fT4 and fT3 tests can detect hypothyroidism or hyperthyroidism even before symptoms appear. TSH is a hormone produced by the pituitary gland that controls thyroid function. Free thyroxine (fT4) and triiodothyronine (fT3) regulate metabolism throughout the body. All three tests are performed from a venous blood sample. Abnormal results may indicate a hormonal disorder affecting fertility. Learn the detailed standards and interpretation of the results to understand the impact of the thyroid on reproduction.

Highlights

  • TSH, FT4, FT3 tests detect thyroid diseases that may prevent pregnancy.
  • It is best to take a blood sample for the TSH test in the morning, as hormone levels fluctuate throughout the day.
  • The normal TSH level is 0.4-5 mIU/L - a higher value suggests hypothyroidism, a lower value hyperthyroidism.
  • FT3 and FT4 tests can be performed at any time of day without the need to be fasting.

Thyroid diseases can prevent pregnancy.

TSH, FT4, FT3 tests are performed to exclude thyroid diseases that prevent pregnancy. The determination of hormone levels is performed from a blood sample.

TSH test

Thyrotropic hormone (thyrotropin, TSH) is produced by the pituitary gland. By testing its concentration in the blood, it is possible to assess the functioning of the thyroid gland and detect its disorders (hypothyroidism and hyperthyroidism) even before the first symptoms of disease appear. It is best to take a blood sample for the test in the morning, as TSH levels can fluctuate throughout the day. There is no need to prepare for the test, but it is important to inform your doctor of any medication you are taking before the test is carried out, as in some cases it is necessary to stop taking them for a short period of time.

Normal thyrotropin levels range from 0.4 to 5 mIU/L. Higher levels of thyrotropin hormone suggest hypothyroidism and may also be a symptom of pregnancy. Lower TSH hormone levels indicate hyperthyroidism, and may also be related to medication (e.g. steroid medication), Graves-Basedow disease, excess iodine in the body or the use of excessive doses of thyroid hormone medication.

The result of a thyrotropin level test is not enough to make a diagnosis - fT3 (free triiodothyronine) and fT4 (free thyroxine) are usually also measured.

Testing fT3

Thyroid conditions can cause a decrease in fertility in women, so when trying fruitlessly to have a baby, it is worth testing thyroid hormone levels. One of these is fT3, or free triiodothyronine. Testing fT3 levels in the blood allows the function of the thyroid gland to be assessed and its diseases to be detected - however, values for other hormones in this group, namely TSH (thyrotropic hormone) and fT4 (free thyroxine), need to be determined to make a diagnosis.

A venous blood sample, taken at any time, is required for the test. The patient does not need to be fasting. A high concentration of free triiodothyronine suggests excessive activity of the thyroid gland (so-called hyperthyroidism), but may also indicate an iodine deficiency in the body. A low fT3 result indicates hypothyroidism, and may also be related to another debilitating disease or past surgery.

Testing fT4

The proper functioning of the entire organism - including the reproductive system - largely depends on the proper function of the thyroid gland and the amount of hormones it produces. One of these is the hormone fT4 (so-called free thyroxine), which regulates metabolic processes. Testing the fT4 level in the blood serves to assess the functioning of the thyroid gland and to monitor the effectiveness of the treatment carried out when diagnosed with a disease within this organ.

A blood sample for the test can be taken at any time of day, without the need to be fasting. Elevated levels of free thyroxine may indicate hyperthyroidism or an excess of thyroid hormones in the body, resulting from the use of hormone medication. Low values for fT4 as a result of the test indicate hypothyroidism or severe iodine deficiency.

  1. Bednarczuk, T., Miśkiewicz, P. (2007). Hypothyroidism in pregnancy. Practical Medicine - Endocrinology. Accessed: https://www.mp.pl/pacjent/endokrynologia/choroby/79804
  2. Gietka-Czernel, M., Jastrzębska, H. (2007). The TSH norm - should it be changed? Endocrynologia Polska, 58(5), 454-458. DOI: https://journals.viamedica.pl/endokrynologia_polska/article/download/25608/20431.
  3. Zgliczynski, W. (ed.). (2020). Great Internal Medicine. Endocrinology, Volume I (2nd edition). Warsaw: Medical Tribune Polska, ISBN 978-83-957198-6-8.

The medical information presented should be considered as general guidelines and does not replace the individual judgement of the doctor regarding the medical management of each patient. The doctor, after a thorough examination of the patient's condition, determines the extent and frequency of diagnostic tests and/or therapeutic procedures, taking into account specific medical indications. All medical decisions are made in full consultation with the patient.

Author of the article

Invimed editorial team - we serve patients by solving their fertility problems. We use world medical knowledge, state-of-the-art technology and treatment methods. We are here to make dreams of parenthood come true. The smiles on the faces of happy parents give meaning to our work.

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