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Medical Author:

Stephanie L Lee, MD, PhD, FACE

Medical Editor:

Melissa Conrad Stöppler, MD, Chief Medical Editor

Melissa Conrad Stöppler, MD, Chief Medical Editor

Melissa Conrad Stöppler, MD, is a U.S. board-certified Anatomic Pathologist with subspecialty training in the fields of Experimental and Molecular Pathology. Dr. Stöppler's educational background includes a BA with Highest Distinction from the University of Virginia and an MD from the University of North Carolina. She completed residency training in Anatomic Pathology at Georgetown University followed by subspecialty fellowship training in molecular diagnostics and experimental pathology.

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Medical Editor:

Jerry R. Balentine, DO, FACEP

Jerry R. Balentine, DO, FACEP

Dr. Balentine received his undergraduate degree from McDaniel College in Westminster, Maryland. He attended medical school at the Philadelphia College of Osteopathic Medicine graduating in1983. He completed his internship at St. Joseph's Hospital in Philadelphia and his Emergency Medicine residency at Lincoln Medical and Mental Health Center in the Bronx, where he served as chief resident.

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Newly diagnosed hyperthyroidism occurs in about 1 in 2,000 pregnancies. Graves' disease accounts for 95% of cases of hyperthyroidism newly diagnosed during pregnancy.

As with hypothyroidism, many symptoms of mild hyperthyroidism mimic those of normal pregnancy. However, anyone experiencing symptoms such as significant weight loss, vomiting, increased blood pressure, or persistently fast heart rate should have blood tests to evaluate whether hyperthyroidism is present.

Mild or subclinical hyperthyroidism defined as a lower than normal TSH and normal Free T4 level is not dangerous to the mother or baby and does not need to treated. Thyroid tests should be checked again in 4 weeks. However, untreated moderate to severe hyperthyroidism does cause fetal and maternal complications including poor weight gain and tachycardia (an abnormally fast heart rate).

There are new recommendations for the treatment of hyperthyroidism during pregnancy Propylthiouracil is used during the first trimester to block the synthesis of thyroid hormone and to bring thyroid hormone levels to borderline or slightly higher than normal levels. Propylthiouracil has a lower risk of some rare fetal malformations compared to methimazole (Tapazole) and is preferred during the critical fetal developmental period during the first trimester. Propylthiouracil is not recommended during the remainder or pregnancy because of the risk of serious hepatitis. During the second and third trimester, propylthiouracil should be switched to methimazole. The incidence rate of side effects for each medication is not increased in pregnancy.

Iodine will cross the placenta, so its use in either a thyroid scan or in treatment with radioactive iodine is prohibited in pregnancy.

One positive note for women with hyperthyroidism is that those with Graves' disease or Hashimoto's thyroiditis may have improvement in their symptoms as the pregnancy progesses.

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