Thyroid-stimulating hormones (TSH) help regulate your body’s production of thyroid hormone. High TSH levels mean your thyroid is underperforming, while low levels mean you’re producing too much.
Your pituitary gland produces thyroid-stimulating hormones (TSH), which help regulate the production of thyroid hormones.
TSH levels change inversely with how much thyroid hormone is in your body. If your pituitary gland produces more TSH, your thyroid will produce more hormones. The two glands work together to make sure the right amount of thyroid hormone is being produced.
- High TSH levels usually mean that your thyroid is underperforming. Your pituitary gland reacts to a lack of thyroid hormones by producing extra TSH to make up the difference. This is called hypothyroidism.
- Low TSH levels usually mean that you’re producing too much thyroid hormone. Your pituitary gland responds accordingly by decreasing TSH production to regulate thyroid function. This is called hyperthyroidism.
Doctors use TSH blood tests to assess whether your TSH levels are in the normal or targeted range.
The targeted range of TSH for an adult is 0.4 to 4.0 milli-international units per liter (mU/L). However, that range can vary according to your age, whether you’re pregnant, or whether you’re already being treated for a thyroid disorder.
If you’re taking thyroid hormone replacement medication, the targeted TSH range is 0.5 to 3.0 nU/L.
This article reviews the TSH reference ranges for different age groups and for pregnant people.
The estimated TSH reference ranges for adults based on age are as follows:
| Age range | Targeted TSH ranges | Low TSH | High TSH |
| 18 to 30 years | 0.5 to 4.1 mU/L | < 0.5 mU/L | > 4.1 mU/L |
| 31 to 50 years | 0.5 to 4.1 mU/L | < 0.5 mU/L | > 4.1 mU/L |
| 51 to 70 years | 0.5 to 4.5 mU/L | < 0.5 mU/L | > 4.5 mU/L |
| 71 to 90 years | 0.4 to 5.2 mU/L | < 0.4 mU/L | > 5.2 mU/L |
TSH tends to be high for the first month after a child is born. As they approach adulthood, TSH levels gradually decrease before rising again as they age.
The TSH reference ranges in children based on their age are as follows:
| Age | Targeted TSH ranges |
| at birth | 3.84 to 11.75 mU/L |
| 1 month | 1.18 to 3.57 mU/L |
| 1 years | 1.17 to 3.55 mU/L |
| 5 years | 1.15 to 3.47 mU/L |
| 12 years | 1.09 to 3.31 mU/L |
| 18 years | 1.05 to 3.16 mU/L |
Pregnancy can significantly affect the thyroid gland and its function due to the body’s increased metabolic needs. For example, during pregnancy, a maternal body may require 40% to 100% more thyroid hormones to meet the needs of the mother and fetus.
Pregnant people without thyroid disease don’t usually need additional thyroid hormone supplements as their bodies naturally make more thyroid hormone during pregnancy to provide enough for themselves and their baby.
But if you are already being treated for hypothyroidism, you may need to increase your dose of thyroid hormone supplements. For this reason, it’s important to monitor TSH levels during your pregnancy:
- as soon as you know you’re pregnant
- every 4 to 6 weeks during pregnancy
- 2 to 4 weeks after pregnancy
The TSH reference ranges during pregnancy are as follows:
| Stage of pregnancy | Targeted TSH ranges | Low TSH | High TSH |
| first trimester | 0.6 to 3.4 mU/ | < 0.6 mU/L | > 3.4 mU/L |
| second trimester | 0.37–3.6 mU/L | < 0.37 mU/L | > 3.6 mU/L |
| third trimester | 0.38–4.0 mU/L | < 0.38 mU/L | > 4.0 mU/L |
If you are pregnant, let your doctor know about any thyroid disorders you have
If you have a preexisting thyroid disorder, be sure to let your doctor or obstetrician-gynecologist know. They can help you manage your condition during and after pregnancy.
A doctor may recommend one or more of the following treatments for abnormal levels of TSH:
Hypothyroidism (high TSH)
- daily thyroid hormone medications, such as levothyroxine
- natural thyroxine hormone extracts and supplements
- consuming less of substances that affect levothyroxine absorption, such as fiber, soy, iron, or calcium
Hyperthyroidism (low TSH)
- oral radioactive iodine to shrink your thyroid gland
- methimazole or propylthiouracil to keep your thyroid from making too much thyroid hormone
- removal of your thyroid gland if regular treatments don’t work or may be threatening to your health, such as during pregnancy
Abnormal TSH levels can indicate that your thyroid gland isn’t functioning properly. This can lead to long-term complications if you have an underlying condition such as hypo- or hyperthyroidism.
If you have a family history of thyroid disorders or have had abnormal TSH levels on previous test results, make sure you get your TSH levels tested regularly.
Follow any instructions your doctor provides, such as stopping certain medications or avoiding specific foods before a TSH test, to ensure accurate results.