A breastfeeding infant, screened for congenital hypothyroidism, is found to have low levels of thyroxine (T4) and high levels of thyroid-stimulating hormone (TSH). What is the best explanation for this finding?

The thyroxine level is low because the TSH level is high.

High thyroxine levels normally occur in breastfeeding infants.

The thyroid gland does not produce normal levels of thyroxine for several weeks after birth.

The TSH is high because of the low production of T4 by the thyroid.