Thyroid Stimulating Hormone - All You Need To Know About TSH

Written By Nivetha Arulraj - March 05, 2025

Read Time - 3 min read

Thyroid, a butterfly-shaped gland located near your throat, may potentially affect fertility. TSH testing is a way to monitor your thyroid function. The test determines how much thyroid-stimulating hormone (TSH) your body produces, provides information about thyroid health, helps diagnose thyroid disorders and monitor treatment for the same.

What Is Thyroid Stimulating Hormone?

Thyroid stimulating Hormone (TSH), also known as thyrotropin is a hormone that acts as a messenger to the thyroid gland. It is produced by the pituitary gland, a pea shaped tiny organ found at the base of the brain.

Role Of Thyroid Stimulating Hormone

TSH regulates the production of the thyroid hormones, namely, thyroxine (T4) and triiodothyronine (T3). TSH released from the pituitary gland eventually binds with the receptors in the thyroid gland. At this point, everything kicks into gear which leads to the release of T4 and T3 into the bloodstream. Increase in the T4 and T3 levels beyond a certain threshold ceases the production of TSH. This mechanism helps keep the hormone levels balanced. Reduction in T4 and T3 levels further results in the production of TSH. In short, the amount of TSH present in the bloodstream is totally dependent on the levels of T3 and T4. These hormones in turn control your body functions that help maintain the body’s metabolic rate, heart and digestive functions, muscle control, brain development, and maintenance of bones.¹

Understanding Thyroid Disorders

A TSH test is often performed to find out how the thyroid is functioning. Abnormal levels of TSH indicate the occurrence of thyroid disorders - hypothyroidism or hyperthyroidism.

Fact:

If your thyroid levels are found to be higher than normal, it may indicate poor thyroid function wherein the gland is not producing enough of the thyroid hormones (T4 & T3). This condition is known as Hypothyroidism. In contradiction, If your thyroid levels are found to be lower than normal, it may indicate over production of the thyroid hormones known as Hyperthyroidism. These disorders may impact fertility by ²:

Disrupting the menstrual cycle making it difficult to conceive
Interfering with the release of eggs from the ovary (ovulation)
Increasing the risk of early-term miscarriage
Increasing the risk for premature birth

Hypothyroidism is further classified as:

Primary hypothyroidism, in which the thyroid glands are damaged. This ceases the hormone production. As a response to this, the pituitary gland and hypothalamus produce elevated levels of TSH.
Secondary hypothyroidism is marked by a malfunction of the pituitary gland or the hypothalamus. As a result, low levels of TSH are produced. Since TSH directly regulates the thyroid gland, the hormones produced by the thyroid gland are also low.

Similarly, Hyperthyroidism is also classified as:

Primary hyperthyroidism is marked by a malfunction of the thyroid gland. Decreased TSH levels and high levels of FT4 coupled with menstrual irregularity are collectively required to establish a diagnosis for Primary Hypothyroidism.
Secondary hyperthyroidism is marked producing excess TSH. Since TSH regulates the thyroid gland, excess TSH stimulates the thyroid gland to produce excess thyroid hormones.

Implication:

Both hyper and hypothyroidism may negatively impact fertility by affecting both - the ability to get pregnant as well as carry a child to term ². Should your results indicate a thyroid disorder, consult your doctor and take corrective measures.

When Can I Do A TSH Test?

Your TSH test does not require any special preparations. It can be performed anytime during the day. However minor diurnal variations are noted in thyroid hormone levels.

What Can Differing TSH Levels Tell You?

1. Normal TSH Levels

A normal reference range for TSH is somewhere between 0.3-4.2 micro-international units per liter (µIU/mL).

2. High TSH Levels

An overactive thyroid or Hyperthyroidism is a sign of high levels of production of the hormone. The primary purpose of this hormone is to work the body’s metabolism. Therefore, women with hypothyroidism will most likely have symptoms associated with slow metabolism. Some common signs to keep an eye out for ^{3 4}

Tremor in hands
Puffiness
Anxiety
Weight Loss
Difficulty in Sleeping
Increased Heart Rate
Bulging of the eyes
Hair Loss

3. Low TSH Levels

An underactive thyroid or Hypothyroidism is a sign that your body is producing too little of the hormone. When left untreated, hyperthyroidism can cause issues concerning menstrual cycles, bone, muscle health and fertility. At the time of pregnancy too, if left untreated, hyperthyroidism can create problems concerning the health and well being of the mother. Some common signs to keep an eye out for ^{2 3 4}