Transient Hyperthyroidism of Hyperemesis Gravidarum in Pregnancy

Updated September 02, 2014.

During the first trimester of pregnancy, a small percentage of women develop a form of hyperthyroidism that is triggered by a severe form of morning sickness known as hyperemesis gravidarum.

This short-term hyperthyroidism, known as transient hyperthyroidism of hyperemesis gravidarum, or THHG, is characterized by severe nausea, excessive vomiting, electrolyte disturbances, and weight loss. Other symptoms can include fatigue, weakness, excessive salivation, lightheadedness, fainting, and infrequent urination.

Hyperthyroidism is not linked to most cases of hyperemesis gravidarum. But distinct factors distinguish THHG from other hyperthyroidism in pregnant women:

• the presence of severe vomiting -- not characteristic of typical hyperthyroidism
• significant weight loss -- which is not characteristic during pregnancy
• lack of typical Graves' disease symptoms, including goiter (enlarged thyroid, and ophthalmopathy (eye-related thyroid symptoms)
• lack of other "classic" hyperthyroidism symptoms such as tachycardia (a rapid heartrate greater than 100 beats/minute), diarrhea, muscle weakness, or tremor

Blood tests can also help pinpoint a diagnosis of THHG because free T4 is usually only slightly elevated, and the T3 level will typically be normal in a woman with THHG, whereas both free T4 and T3 are clearly elevated in hyperthyroidism.

Treatment for Transient Hyperthyroidism of Hyperemesis Gravidarum

Some cases of THHG require no thyroid-specific treatment, and the thyroid abnormalities will spontaneously resolve by the end of the second trimester.
When symptoms are severe, however, thyroid treatment may take place, usually during the first trimester, and may consist of a short course of antithyroid drugs.

As pregnancy hormones normalize after the first trimester, and by weeks 16 to 20, many women will find that the hyperthyroid symptoms subside. TSH may remain suppressed however, even while the thyroid function returns to normal. Treatment may then be able to be discontinued, and thyroid function usually returns to normal before delivery.

In dealing with THHG that involves milder nausea and vomiting, treatment usually involves dietary changes, rest and antacids. On the alternative front, some women have had success with acupressure, herbal remedies such as peppermint and ginger, and hypnosis.

When nausea and vomiting are severe, dehydration and malnutrition in the mother and poor weight gain in the developing baby can occur. Severe symptoms, therefore, may require hospitalization so that the woman can receive intravenous fluids and nutrition. In some severe cases, medications, including metoclopramide (Reglan), antihistamines, and antireflux medications, may also be prescribed.

<sub>Sources:

Lazarus, JH."Thyroid disorders associated with pregnancy: etiology, diagnosis, and management." Treatments in Endocrinology 2005;4(1):31-41. Abstract

Braverman, MD, Lewis E., and Robert D. Utiger, MD. Werner and Ingbar's The Thyroid: A Fundamental and Clinical Text. 9th ed., Philadelphia: Lippincott Williams & Wilkins (LWW), 2005.</sub>