A case of a preterm infant born to a mother with undiagnosed Graves’ disease who developed late onset hyperthyroidism

Abstract

 This case involves a preterm infant born at 34 weeks of gestation, who remained stable in terms of respiratory and circulatory status after birth. On day 21 of life, direct bilirubin increased to 1.5 mg/dL, prompting further investigation. The infant was found to have hyperthyroidism, with TSH ＜ 0.01 μU/mL and free T4 at 3.24 ng/dL. Additionally, thyroid-stimulating antibody（TSAb）was positive. Treatment with methimazole was initiated on day 21 of life, and by day 48, direct bilirubin had normalized. The mother was asymptomatic; however, on postpartum day 22, she was found to be TSAb-positive and was diagnosed with Graves’ disease. Retrospective serum analysis at birth showed that both the mother and infant had undetectable TSH levels, while free T4 remained within the normal range. The mother tested positive for both TSAb and TSH stimulation-blocking antibody（TSBAb）, suggesting that both antibodies had been transferred to the infant. By day 37 of life, the infant remained TSAb-positive, while TSBAb had become negative. During late pregnancy, TSBAb influenced thyroid function, keeping it normal in both the mother and infant. However, after birth, TSBAb disappeared first, leading to the delayed onset of neonatal hyperthyroidism.