Hyperthyroidism in Pregnancy

Hyperthyroidism in pregnancy is usually caused either by Graves’ disease or Hyperemesis Gravidarum.

Graves’ Disease 

This is an autoimmune disorder. Here the body build up antibodies against specific cells of its own tissues. An antibody called Thyroid-Stimulating Immunoglobulin (TSI) is produced. This mimics TSH and causes the thyroid to make too much thyroid hormone.

Graves’ disease flares up during first trimester of pregnancy. In the later two trimesters, however, a disappearance of signs and symptoms of this disorder occurs. This results from the general suppression of the immune system that occurs during pregnancy. The disease usually worsens again in the first few months after delivery. Pregnant women with Graves’ disease should be monitored monthly.

Hyperemesis Gravidarum

Rarely, hyperthyroidism in pregnancy is caused by Hyperemesis Gravidarum. This is a condition characterized by severe nausea and vomiting. This can lead to weight loss and dehydration. The condition is believed to be triggered by high levels of HCG, which can also lead to temporary hyperthyroidism that goes away during the second half of pregnancy.

Effects of Hyperthyroidism on Mother and Baby

Uncontrolled hyperthyroidism during pregnancy can lead to:

  • Preeclampsia- High rise in blood pressure in late pregnancy.
  • Thyroid storm- Sudden, severe worsening of symptoms.
  • Miscarriage
  • Premature birth
  • Low birth weight

If a woman has Graves’ disease was treated in the past with surgery or radioactive iodine, the TSI antibodies can still be present in the blood, even when thyroid levels are normal. The TSI antibodies she produces may travel across the placenta to the baby’s bloodstream and stimulate the fetal thyroid. If the mother is being treated with antithyroid medications, hyperthyroidism in the baby is less likely because these medications also cross the placenta.

Hyperthyroidism in a newborn can result in:

  • Rapid heart rate, which can lead to heart failure;
  • Early closure of the soft spot in the skull;
  • Poor weight gain;
  • Irritability;
  • Enlarged thyroid that can press against the windpipe and interfere with breathing.

Women with Graves’ disease and their newborns need to be closely monitored by their doctor throughout pregnancy.

Diagnosing Hyperthyroidism in Pregnancy

It is difficult to diagnose hyperthyroidism in pregnancy only by doing blood tests to measure TSH, T3, and T4 levels. Symptoms need to be watched closely.

Some symptoms of hyperthyroidism are common features in normal pregnancies, including increased heart rate, heat intolerance, and fatigue.

Other symptoms are more closely associated with hyperthyroidism. They include:

  • Rapid and irregular heartbeat,
  • A slight tremor,
  • Unexplained weight loss or failure to have normal pregnancy weight gain,
  • Severe nausea and vomiting associated with hyperemesis gravidarum.

If a pregnant woman’s symptoms suggest hyperthyroidism, her doctor will probably first perform the ultrasensitive TSH test. This test detects even tiny amounts of TSH in the blood and is the most accurate measure of thyroid activity available.

If TSH levels are low, another blood test is performed to measure T3 and T4. Elevated levels of free T4, the portion of thyroid hormone not attached to thyroid-binding protein confirms the diagnosis.

TSI test– This is a test for the presence of TSI antibodies. This antibody is specific for Grave’s disease

Treating Hyperthyroidism During Pregnancy

Mild hyperthyroidism, in which TSH is low but free T4 is normal, does not require treatment. More severe hyperthyroidism is treated with antithyroid medications, which act by interfering with thyroid hormone production.

Radioactive iodine treatment is not an option for pregnant women because it can damage the fetal thyroid gland. Surgery to remove all or part of the thyroid gland can be done in women who cannot tolerate antithyroid medications.

Antithyroid medications cross the placenta in small amounts and can decrease fetal thyroid hormone production, so the lowest possible dose should be used to avoid hypothyroidism in the baby.

Stop your antithyroid medication and call your health care provider right away if you develop any of the following signs and symptoms:

  • Fatigue
  • Weakness
  • Vague abdominal pain
  • Loss of appetite
  • Skin rash or itching
  • Easy bruising
  • Yellowing of the skin or whites of the eyes
  • Persistent sore throat
  • Fever

Some women are able to stop antithyroid medication therapy in the last 4 to 8 weeks of pregnancy due to the remission of hyperthyroidism that occurs during pregnancy. However, they should continue to be monitored for recurrence of thyroid problems following delivery.

Read about how to deal with Hypothyroidism in Pregnancy.