A Newborn Boy Is Found to Have Markedly Elevated Serum

A newborn boy is found to have markedly elevated serum TSH and low thyroxine on routine screening.  Laboratory findings using a venous blood sample confirm the diagnosis.  The patient was born at 39 weeks gestation to a 34-year-old healthy woman, who had been taking prenatal vitamins regularly.  He has no symptoms or abnormal findings on clinical examination.  Imaging studies reveal an ectopic thyroid gland just below the tongue.  Which of the following is the most likely cause of this patient's otherwise normal physical examination despite abnormal thyroid laboratory findings?

A) Excess thyroxine production by an ectopic thyroid
B) Increased thyroid-binding globulin in pregnancy
C) Transplacental transfer of thyroid-stimulating antibody
D) Transplacental transfer of thyroxine
E) Transplacental transfer of TSH

Correct Answer:

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