Hyperthyroidism in pregnancy

Definition

Overactive thyroid is an increased activity of the thyroid gland, which thus produces the hormones triiodothyronine (T3) and thyroxine (T4) more strongly. This leads to an increase in the size and volume of the thyroid gland. The produced hormones are essential for the human organism and cause an accelerated metabolism with many resulting symptoms if the effective levels are too high. An overactive thyroid during pregnancy may have already existed before this due to Graves’ disease or thyroid autonomy. However, if the hyperthyroidism is new, it is called pregnancy-associated hyperthyroidism.

Causes of hyperthyroidism in pregnancy

An overactive thyroid during pregnancy can have various causes. Hyperthyroidism often exists before pregnancy, mostly due to Graves’ disease. Thyroid autonomy or an inflamed thyroid gland can also be possible causes.

However, hyperthyroidism can also reappear during pregnancy. This is most likely in the first trimester, i.e. the first trimester of pregnancy. Pregnancy-associated hyperthyroidism can be caused by a greatly increased hCG level in the blood.

This hormone, which is produced in the placenta, is elevated in every pregnancy, especially in the first trimester and especially in multiple pregnancies. However, even at extremely high levels, it can be the expression of an underlying trophoblast disease. HCG has a stimulating effect on the thyroid gland and thus causes an increase in size and function, which leads to hyperfunction.

Pregnancy-associated hyperthyroidism rarely becomes symptomatic. In most cases, the values are elevated but have no disease value (subclinical hyperthyroidism) and only require regular follow-up. In most cases, hyperthyroidism is self-limiting due to decreasing HCG levels from the second half of pregnancy onwards and does not require medication.

Diagnosis

If there is a suspicion of a new hyperthyroidism during pregnancy or to monitor the course of an already known hyperthyroidism, a detailed medical history is first taken. Here, the focus is on thyroid-specific symptoms. This is followed by a palpation of the thyroid gland.

Blood is also taken to check thyroid gland values (TSH, fT3, fT4) and possible antibodies. The hCG value can also be taken, which can play a role in pregnancy-associated hyperthyroidism. In addition, an ultrasound of the neck is performed to assess the size and volume of the thyroid gland.