Hypothyroidism in pregnancy

What causes hypothyroidism in pregnancy?

Hypothyroidism in pregnancy is usually caused by Hashimoto’s disease and occurs in one to three of every 1,000 pregnancies.Like Graves’ disease, Hashimoto’s disease is an autoimmune disorder. In Hashimoto’s disease, the immune system makes antibodies that attack cells in the thyroid and interfere with their ability to produce thyroid hormones. White blood cells also invade the thyroid and decrease thyroid hormone production.

Hypothyroidism in pregnancy can also result from existing hypothyroidism that is inadequately treated or from prior destruction or removal of the thyroid as a treatment for hyperthyroidism.

How does hypothyroidism affect the mother and baby?

Some of the same problems caused by hyperthyroidism can occur in hypothyroidism. Uncontrolled hypothyroidism during pregnancy can lead to

  • congestive heart failure
  • preeclampsia
  • anemia-a disorder in which the blood does not carry enough oxygen to the body’s tissues
  • miscarriage
  • low birthweight
  • stillbirth

Because thyroid hormones are crucial to fetal brain and nervous system development, uncontrolled hypothyroidism-especially during the first trimester-can lead to cognitive and developmental disabilities in the baby.

How is hypothyroidism in pregnancy diagnosed?

Like hyperthyroidism, hypothyroidism is diagnosed through a careful review of symptoms and measurement of TSH and T4 levels.

Symptoms of hypothyroidism in pregnancy include extreme fatigue, cold intolerance, muscle cramps, constipation, and problems with memory or concentration. High levels of TSH and low levels of free T4 generally indicate hypothyroidism. Because of normal pregnancy-related changes in thyroid function, test results must be interpreted with caution.

The TSH test can also identify subclinical hypothyroidism-a mild form of hypothyroidism that has no apparent symptoms. Subclinical hypothyroidism occurs in two to three of every 100 pregnancies. Test results will show high levels of TSH and normal free T4. Experts have not reached a consensus as to whether asymptomatic pregnant women should be routinely screened for hypothyroidism. But if subclinical hypothyroidism is discovered during pregnancy, treatment is recommended to help ensure a healthy pregnancy.

How is hypothyroidism treated during pregnancy?

Hypothyroidism is treated with synthetic thyroxine, which is identical to the T4 made by the thyroid gland. Women with pre-existing hypothyroidism will need to increase their prepregnancy dose of thyroxine to maintain normal thyroid function. Thyroid function should be checked every 6 to 8 weeks during pregnancy. Synthetic thyroxine is safe for the fetus and necessary for its well-being if the mother has hypothyroidism.