Pregnancy significantly affects the thyroid gland and its function due to increased metabolic needs. For example, a maternal body requires 40% to 100% more thyroid hormones to meet the needs of the mother and fetus during pregnancy.

For this reason, checking thyroid function before, during, and after pregnancy is critical, particularly for those with preexisting thyroid conditions.

People with hypothyroidism (underactive thyroid) who are already taking thyroid hormone supplements typically need to increase their dose during pregnancy, usually by 20 to 30%.

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.

Generally speaking, if you are pregnant and have a history of thyroid disease, or are currently being treated for hypothyroidism, your thyroid levels should be checked:

  • as soon as you know you’re pregnant
  • every 4 to 6 weeks during pregnancy
  • 2 to 4 weeks after pregnancy

Work closely with a doctor if you are pregnant and have a preexisting thyroid disorder

If you have a preexisting thyroid disorder, be sure to let your doctor or obstetrician-gynecologist know that you have a thyroid disorder. They can provide information to help you manage your condition during and after pregnancy.

If you don’t have a history or risk factors for thyroid disease, routine thyroid testing at the start of pregnancy isn’t generally recommended.

If your clinician does check your thyroid hormone levels and they’re normal, you typically don’t need repeat testing unless you develop symptoms or risk factors later.

How are thyroid levels tested?

Blood TSH (thyroid-stimulating hormone) levels are the recommended first-line test for thyroid function assessment in pregnancy. If TSH is abnormal, free T4 levels (thyroid hormone) are measured.

In some cases, thyroid antibodies may also be tested, especially in those with a family history of thyroid disease or other autoimmune conditions.

Learn more about thyroid function tests and what the results indicate here.