Thyroid Problems in a Pregnancy
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Thyroid Problems in a Pregnancy

A basic understanding of the thyroid function and test results is needed to understand thyroid problems during a pregnancy. The thyroid makes hormones referred to as T4 and T3; both are vital to the healthy functioning of the mom’s body and the growing baby. Thyroid stimulating hormone (TSH), produced by the pituitary gland, tells the thyroid just how much T4 and T3 to produce. Blood tests measure TSH, T4 and T3 levels, although typically only the close monitoring of TSH and T4 is necessary. Although the effects of thyroid problems left untreated in pregnancy can be severe, it is important to know that–with close monitoring and treatment–most women with thyroid problems in pregnancy have healthy babies, according to the March of Dimes.

Thyroid Test Results in Pregnancy

Due to the hormonal changes during pregnancy, the various thyroid-related hormones, such as TSH and Total T4, normally tested and used to monitor thyroid function, are affected. For example, often in pregnancy, TSH test results are low in the first trimester and return to normal in the second and third trimester. For those with a pre-existing thyroid condition, this can make monitoring the thyroid during pregnancy more difficult. You doctor may choose to monitor Free T4 levels rather than TSH levels during pregnancy. This is often a better measurement of the thyroid’s function during pregnancy because, in patients without a thyroid condition, the Free T4 levels remain normal throughout pregnancy, according to the American Thyroid Association. It is recommended that patients be tested every six to eight weeks throughout the pregnancy.


Hyperthyroidism means the thyroid is producing too much thyroid. Test results would show a low TSH (because the pituitary is telling the thyroid to slow down) and high T4 levels. For both the mom and the baby, when left untreated, this may cause an irregular heartbeat and can cause the baby to grow slowly, have a premature birth or congenital deformities, according to the American Thyroid Association.


With hypothyroidism, the thyroid produces too few thyroid hormones. Test results will show a high TSH (because the pituitary gland is telling the thyroid to work harder) and low T4 levels. The American Thyroid Association reports that for the mom, hypothyroidism can lead to heart failure, preeclampsia and anemia. For the baby, this condition can cause low birth weight and brain function problems.


When monitored through regular blood tests, both hyperthyroidism and hypothyroidism are usually easily treated and do not become elevated to a serious condition. In patients with an overactive thyroid, monitoring may be all that is needed, but medications to lower the thyroid hormone levels can be used if necessary. In patients with an underactive thyroid, thyroid hormone replacement medication is often prescribed. In the United States, all babies are tested for thyroid function at birth. If the baby is not producing enough thyroid hormone, treatment starts immediately and usually prevents any problems associated with hypothyroidism, such as brain function problems.

Post Pregnancy

If you had thyroid problems before or during pregnancy, it is vital you continue to see your doctor and monitor your thyroid levels post-pregnancy. The weeks following the birth of your child come with swings in hormone levels, including thyroid. These changes may mean you need adjustments to your medication several times in the following months. Thyroid problems post-pregnancy can affect milk supply and worsen postpartum depression.

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  • amor maternal image by Leonardo Jerez from
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