Shift in Dominance from Blocking to Stimulating Type of Thyrotropin Receptor Antibodies, Resulting in Conversion from Hypothyroidism to Hyperthyroidism during Late Pregnancy.

A 20-year-old woman with a 10-month history of treatment for Graves' disease (GD), developed hypothyroidism with a high level of thyrotropin (TSH) receptor-blocking antibodies (TBAbs). She conceived at 28 years old and was clinically euthyroid in the first and second trimester, while taking L-thyroxine. However, at 28 weeks she became hyperthyroid with an unexpected rise in TSH receptor-stimulating antibody (TSAb) levels. She was diagnosed with GD, and methimazole was initiated. Her thyroid function normalized, but the neonate became hyperthyroid. We herein report the first case of a shift in dominance from TBAbs to TSAbs in late pregnancy.