Transient congenital hypothyroidism due to maternal factor

Transient congenital hypothyroidism due to maternal factor is a temporary form of thyroid hormone deficiency present at birth that is caused by substances or conditions originating from the mother that cross the placenta and affect the newborn's thyroid function. The most common maternal factors include the transplacental passage of maternal thyrotropin receptor-blocking antibodies (TRBAb), maternal use of antithyroid medications (such as propylthiouracil or methimazole used to treat maternal Graves' disease or other hyperthyroid conditions), and excessive maternal iodine intake or deficiency. These maternal factors temporarily suppress the newborn's thyroid gland function, leading to reduced production of thyroid hormones (T3 and T4) and elevated thyroid-stimulating hormone (TSH) levels. Affected newborns may present with clinical features typical of congenital hypothyroidism, including prolonged jaundice, feeding difficulties, constipation, hypotonia (decreased muscle tone), large fontanelles, macroglossia (enlarged tongue), dry skin, hypothermia, and lethargy. If untreated, even transient hypothyroidism during the critical neonatal period can impair neurodevelopment. The condition is typically detected through newborn screening programs that measure TSH and/or T4 levels. The key distinguishing feature of this condition is its transient nature — once the maternal factor is cleared from the infant's circulation (typically within weeks to a few months), normal thyroid function is restored. Treatment involves levothyroxine (synthetic thyroid hormone) replacement therapy initiated promptly after diagnosis to ensure normal growth and neurodevelopment during the critical early postnatal period. Therapy is typically continued until the maternal factor has been cleared, after which thyroid function is reassessed. A trial off medication is usually attempted around 2–3 years of age (or earlier if the transient etiology is confirmed) to verify recovery of normal thyroid function. Maternal history, including thyroid disease status and medication use, is essential for establishing the diagnosis and distinguishing this transient form from permanent congenital hypothyroidism.

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