Thyrotoxicosis that develops during pregnancy may be associated with an increased risk of spontaneous abortion, premature labor, or the development of a disorder called toxemia of pregnancy. Exposure to excess amounts of thyroid hormone during pregnancy may also be associated with the delivery of low birth weight infants.
Graves’ disease that develops during pregnancy may be associated with a specific disorder involving the fetus called fetal hyperthyroidism. This disorder may develop when thyroid stimulating immunoglobulins (TSIs) produced by the mother’s immune system cross over through the placenta to enter the fetal bloodstream. Maternal TSIs may bind to TSH receptors located on the surface of follicular cells in the fetal thyroid gland. In doing so, they may stimulate the fetal thyroid gland to produce excess amounts of thyroid hormone. It may be very difficult to confirm a suspected diagnosis of fetal hyperthyroidism during the course of pregnancy. Measurement of maternal TSI levels during the third trimester of pregnancy may provide some indication of risk. Higher TSI levels may be associated with a greater likelihood of developing fetal hyperthyroidism. Ultrasound studies may reveal an accelerated fetal heart rate or enlargement of the fetal thyroid gland.
In cases of suspected fetal hyperthyroidism, measurement of an infant’s TSH and thyroid hormone levels after delivery will usually help to confirm whether there has been any exposure to significant amounts of maternal TSIs. If blood tests reveal evidence of thyrotoxicosis consistent with hyperthyroidism, an infant may be diagnosed with a condition called neonatal Graves’ disease. Infants with neonatal Graves’ disease may present with a range of symptoms and physical findings similar to those observed in adults with Graves’ disease. Characteristic findings may including excessive irritability, restlessness, an increased appetite, increased frequency of bowel movements, an accelerated heart rate, abnormal heart rhythms, an enlarged thyroid gland, and warm, moist skin. Neonatal Graves’ disease is usually a self-limited condition that resolves over the course of a few months. Mild cases may not require any specific treatment beyond careful monitoring. Moderate to severe cases may require treatment with medications that may include antithyroid drugs, beta blockers, potassium iodide, and glucocorticoids.