We report an uncommon case of a patient with Graves’ disease who developed hypothyroidism with markedly elevated TSH receptor antibody levels seven months after giving birth to her first child.

The patient underwent a series of thyroid function and antibody tests. A radioactive iodine uptake scan was withheld because she was caring for her baby.

A 33-year-old woman was diagnosed with hyperthyroidism at the age of 18. Her mother also had a history of thyroid disease. She had been treated intermittently with antithyroid drugs around 10 years. Before becoming pregnant, she was treated with PTU for hyperthyroidism. In March 2022, before delivery, the patient’s TSH receptor antibody (TRAb) level was 5.23%. However, four months postpartum (in August 2022), her TSH level increased and free T4 decreased. By seven months postpartum(in November 2022), the patient developed clinically evident hypothyroidism, and her TSH receptor antibody level rose to 33.7%. She was subsequently treated continuously with levothyroxine. In February 2024, the patient became pregnant again and continued levothyroxine therapy. The newborn’s congenital hypothyroidism screening showed a thyroid-stimulating hormone (TSH) level of 10 μU/ml, which returned to normal upon repeat testing two weeks later. At that time (November 2024), the patient’s TSH receptor antibody level was >50%.

In this case, the patient transitioned from hyperthyroidism to hypothyroidism seven months after her first delivery and has since remained hypothyroid, continuing treatment with levothyroxine. The possible causes to consider include a switch of TSH receptor antibodies from a stimulating type to a blocking type, or hypothyroidism resulting from postpartum thyroiditis.