Thyroid-stimulating hormone or TSH is secreted by the pituitary gland in the brain. This hormone prompts the thyroid gland to secrete Thyroxine(T3) and Triiodothyronine(T4), which control your metabolism and consequently regulate your weight, heart rate, body temperature, and even your moods. TSH levels in the body are tested to check the functioning of your Thyroid gland.
Like FSH and LH, TSH is one of the pituitary hormones that are tested before IVF, but unlike the former two, TSH doesn’t work directly in the ovaries. It stimulates the Thyroid to produce T3 and T4 that regulate the use of your body’s energy.
When T3 and T4 are low, the pituitary has to produce more TSH indicating an underactive thyroid, or Hypothyroidism. Similarly, low levels of TSH in your blood indicate an overactive thyroid, or Hyperthyroidism.
Thyroid imbalance is one of the many causes of infertility in women.
In a study of 400 infertile women, almost 24% were found to have hypothyroid and after that was treated, around 77% of them were able to conceive within 6 weeks to 12 months. But how does thyroid affect your fertility?
Abnormal TSH levels mean your metabolic function is off, which could interfere with ovulation and cause problems in conceiving.
The developing fetus depends upon the mother’s metabolism for its nutrition, and that depends upon an optimal thyroid function. Thyroid problems could cause pregnancy problems such as miscarriage, pre-eclampsia, premature birth. It may also be responsible for improper mental development and low birth-weight in the new-born.
Abnormal TSH is not just a problem for female fertility; it affects the men too. Thyroid problems can impair sperm quality and affect its motility, resulting in fertilization problems.
What is the use of TSH test?
TSH test is part of the regular fertility work-up as an abnormal thyroid can affect your periods, pregnancy potential, and even the development of the baby in the womb. It is used to:
- Find the reason for infertility as thyroid hormone levels are found to be abnormal in almost around 5% of women who have trouble conceiving
- Check the reason for ovarian cysts, which tend to develop in cases of hypothyroidism
- Diagnose the reason for miscarriages, which can happen in women with an over-active thyroid gland (hyperthyroidism)
- See if your light periods and conception problems are due to hyperthyroidism
- During IVF treatment, TSH test is used to see how you will respond to the ovarian stimulation
- See if it is the reason for low sperm count for men
- For screening and detection of thyroid nodules or lumps that may turn malignant if left undiscovered
- Diagnose autoimmune conditions like Graves’ disease, Hashimoto’s thyroiditis, and thyroid cancer
- Check for goiter or thyroid enlargement
- Check if you are responding to thyroid treatment.
When should you do the Thyroid-stimulating hormone test?
TSH is recommended in the below situations:
- Conception problems: If you have been trying to conceive unsuccessfully for the past 12 months or more, you must get your TSH tested. This applies to both men and women.
- Abnormal periods: Very light or irregular periods could be due to a variety of reasons, one of which is a hyper-active thyroid.
- Recurrent miscarriages: Normal thyroid levels are important normal growth and development of the fetus in your womb.
- Anxiety: Panic attacks and anxiety can be caused by an over-active thyroid gland.
- Abnormal weight-gain or loss: Since thyroid gland regulates your metabolism, it directly impacts your body weight and BMR. Hyperthyroidism is associated with a high BMR and excessive weight-loss, while hypothyroidism could do just the reverse. So, if you experience any unreasonable weight-gain or loss, TSH may be required along with other tests
- Fatigue, depression, insomnia: People experience constantly drained, depressed, and insomniac due to many reasons, and one of them is an under-active thyroid. It causes the metabolism of your body to slow down, causing depression like symptoms.
- Constipation or overly frequent bowel movements: Abnormal TSH levels mess up your body functions, including digestion. Thyroid insufficiency often results in constipation and its excess causes the body’s processes to speed up resulting in frequent bowel movements.
- Body ache: Weakness of muscles, cramping and body ache can be seen in people with hypothyroidism. Your doctor may order a thyroid test, if they don’t find any other explanation for your body ache.
- Slow heart rate, dry hair and skin, intolerance to cold: These are all caused by hypothyroidism, and your doctor may order TSH testing if you have any of these symptoms.
TSH is also used to evaluate patients who are suspected to have other thyroid disorders such as goiter, thyroid nodule, thyroid cancer, Graves’ disease, or Hashimoto’s thyroiditis. These disorders can cause hypothyroidism or hyperthyroidism.
Routine screening for hypothyroidism in adults, in the absence of any symptoms, is still debatable. It may help some people with early detection and treatment but not everyone is in favor. However, organizations such as the Endocrine Society and the American Thyroid Association call for routine thyroid screenings by measuring TSH, T3, T4 in adults irrespective of the symptoms.
TSH Testing Details
The levels of Thyroid-stimulating Hormone in the blood are evaluated with the help of a simple blood test. It can also be tested with a prick-test using an at-home testing kit. Thyroid disorders normally cause abnormal production of thyroid hormones: T3 or (triiodothyronine) and T4 (thyroxine), which are also generally tested along with the TSH.
When to get a TSH test done?
TSH testing can be done any day of the month. The levels of this hormone may fall considerably after eating a meal, so the management and diagnosis of hypothyroidism may not be as accurate.
Sample requirement?
A vial of blood will be collected from a vein in your arm for lab testing. For home testing, it requires only a drop of blood via a prick in your finger.
Are there any requirements before testing?
TSH levels in your body are also affected by any medications you take. If you’re taking multivitamins, Biotin, or any other supplements or medicines, you must discuss them with your healthcare provider to ensure they do not interfere with accurate testing.
Thyroid levels also vary with stress, diet, sleep. It is advisable to do the test for TSH early in the morning, after 8 hours of fasting. If you must repeat the test, make sure to do it under the same conditions again.
When can I get the results?
Most labs will give you the results in the same day or the next.
How does Thyroid-stimulating Hormone work?
A small butterfly-shaped gland located in front of the neck, is supposed to take iodine from your diet and convert it into thyroid hormones: T3 and T4, which are responsible for regulating the metabolism of most of your body cells.
When the levels of T3 and T4 in your blood drops, the pituitary increases the production of TSH, which stimulates the thyroid to release more of these hormones into the blood stream. Again, as their level in the blood rises, the pituitary lowers TSH production.
There is another hormone, called TSH releasing hormone (TRH), which is produced by the Hypothalamus in your brain to tell the pituitary how much TSH to produce.
Thyroid hormones are by the hypothalamus-pituitary axis. So, the stimulus goes from Hypothalamus to pituitary to thyroid to regulate the levels of T3 and T4.
What are normal TSH levels?
| Adult women | 0.5 to 5.0 mU/L |
| Underactive-thyroid (hypothyroidism) | > 5 mU/L |
| Overactive-thyroid (hyperthyroidism) | < 0.4 mU/L |
TSH levels in pregnant women
| During the first trimester of pregnancy | 0.2-<2.5 mU/L |
| During the second trimester | 0.3-3 mU/L |
| During the last trimester | 0.3-3 mU/L |
TSH levels in men by age
| 18-50 years | 0.5 to 4.15 mU/L |
| 51 -70 years | 0.5 to 4.59 mU/L |
| Above 70 years | 0.4 to 5.49 mU/L |
What is the ideal TSH level for IVF?
Preconception TSH value is considered ideal at ≤2.5 mU/L and that is usually the target for IVF cycles.
TSH levels are expected to slightly raised by day 14 after embryo transfer, and this elevated TSH has been found to have a protective effect on the pregnancy. In a study of 325 infertile candidates, women who had lower TSH levels by day 14 after FET were also found to have a lower pregnancy rate as compared to those who had elevated TSH levels.
How is fertility affected by low TSH?
Low TSH levels of hyperthyroidism (which affects around 5 percent of women and 3 percent of men in the US) can cause:
- Disruption of the menstrual cycle
- Reduction in sperm count and volume of the ejaculate
- Poor sperm motility and morphology
- Early miscarriages
- Premature deliveries
How is fertility affected by high TSH?
Hypothyroidism was found to be the reason for infertility in 24% of a group of 400 infertile women. If affects your fertility by causing:
- Irregular menstrual cycles
- Difficulty in conceiving due to problems with ovulation
- Poor sperm morphology
- Problems carrying pregnancy to term and greater risk of miscarriage
Additionally, certain autoimmune or pituitary disorders that cause hypothyroidism may also indirectly affect your fertility.
Reasons for low TSH levels (Hyperthyroidism)
Primary hyperthyroidism is the condition ofhaving a low TSH and high thyroid hormones. It affects women 20 times more than it affects men. The main causes are:
- Graves’ disease
- Toxic thyroid nodule
- Thyrotoxicosis caused by multinodular goitre
- Thyroiditis or inflammation of the thyroid
- Thyroid dysfunction caused by drugs such as Amiodarone (because it contains 40% iodine), cancer drugs, Lithium
- Drug-induced hyperthyroidism occurs when the dosage of hormone drugs is not adjusted when treated hypothyroidism
Reasons for high TSH levels (Hypothyroidism)
Primary hypothyroidism is the condition ofhaving a high TSH and low thyroid hormones, and the main causes are:
- Hashimoto’s thyroiditis
- Other autoimmune thyroid diseases
- Injuries to the thyroid
- Thyroidectomy (removal of complete or part of the thyroid gland)
- Medications such as Amiodarone, Lithium, Interleukin-2 (used in leukemia treatments), other cancer drugs like Tyrosine kinase inhibitors
- Thyroid damage due to radiotherapy
- Excessive use of anti-thyroid medications
Early or mild hypothyroidism may present as a persistently elevated TSH and a normal FT4 hormone level. This pattern is called subclinical hypothyroidism and your doctor may recommend treatment. Over time, untreated subclinical hypothyroidism can contribute to heart disease.
Subclinical hypothyroidism: When the thyroid hormone levels are normal but the TSH values are elevated. This may happen during early stages of the disease and can be dealt with proper medical care.
How to bring Thyroid-stimulating hormone to normal?
In addition to the above factors, TSH values in your blood can also be affected by:
- Fasting
- Body weight
- Illness
- Pregnancy
- Medication
- Iodine levels in the body
- Smoking
- Sleep patterns
Making some lifestyle changes can significantly affect TSH levels in some cases and before starting your IVF treatment, your doctor will attempt to bring your thyroid hormones to normal for optimal chances of conceiving.
For more information on Thyroid-stimulating hormone and to order your test, get in touch using the red contact button on this page.
Resources:
Green, K. A., Werner, M. D., Franasiak, J. M., Juneau, C. R., Hong, K. H., & Scott, R. T., Jr (2015). Investigating the optimal preconception TSH range for patients undergoing IVF when controlling for embryo quality. Journal of assisted reproduction and genetics, 32(10), 1469–1476. https://doi.org/10.1007/s10815-015-0549-4
Verma, I., Sood, R., Juneja, S., & Kaur, S. (2012). Prevalence of hypothyroidism in infertile women and evaluation of response of treatment for hypothyroidism on infertility. International journal of applied & basic medical research, 2(1), 17–19. https://doi.org/10.4103/2229-516X.96795
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Thyroid and Weight: American Thyroid Association https://www.thyroid.org/thyroid-and-weight/
Coping with fatigue: British Thyroid Foundation https://www.btf-thyroid.org/coping-with-fatigue
Zhang, Y., Wu, W., Liu, Y. et al. The impact of TSH levels on clinical outcomes 14 days after frozen-thawed embryo transfer. BMC Pregnancy Childbirth 20,677 (2020). https://doi.org/10.1186/s12884-020-03383-z
Nygaard B. (2008). Hyperthyroidism (primary). BMJ clinical evidence, 2008, 0611. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2907936/
Rugge JB, Bougatsos C, Chou R. Screening for and Treatment of Thyroid Dysfunction: An Evidence Review for the U.S. Preventive Services Task Force [Internet]. Rockville (MD): Agency for Healthcare Research and Quality (US); 2014 Oct. (Evidence Syntheses, No. 118.) https://www.ncbi.nlm.nih.gov/books/NBK285870/
Verma, I., Sood, R., Juneja, S., & Kaur, S. (2012). Prevalence of hypothyroidism in infertile women and evaluation of response of treatment for hypothyroidism on infertility. International journal of applied & basic medical research, 2(1), 17–19. https://doi.org/10.4103/2229-516X.96795
Babić Leko, M., Gunjača, I., Pleić, N., & Zemunik, T. (2021). Environmental Factors Affecting Thyroid-Stimulating Hormone and Thyroid Hormone Levels. International journal of molecular sciences, 22(12), 6521. https://doi.org/10.3390/ijms22126521