Congenital hypothyroidism is present at birth. Most cases are sporadic (85%), with the remainder (15%) due to an inborn error of thyroid hormone synthesis. Most neonates are asymptomatic due to maternal thyroxine (T4) or residual functioning thyroid tissue, but many have a relatively higher birth weight percentile and head circumference percentile than birth length percentile due to myxedema.

When untreated, infants develop symptoms of congenital hypothyroidism including intellectual disability, lethargy, hoarse cry, poor feeding, constipation, myxedema facies, macroglossia, umbilical hernia, large fontanelles, and prolonged jaundice.

Causes of congenital hypothyroidism include thyroid dysgenesis (most common in the United States), thyroid agenesis, iodine deficiency, or dyshormonogenetic goiter.

Congenital hypothyroidism is one of the most common preventable causes of intellectual disability. As
such, newborn screening for thyroid deficiency was initiated in the 1970s.

Related topic: Hypothyroidism