Feeding is poor and the infant may choke frequently. Constipation is common. Affected children do not cry much, but sleep excessively and are sluggish and inactive. Muscle tone is usually decreased. If untreated, hypothyroidism can lead to severe mental retardation and growth retardation.
Development is delayed early on, often indicated by failure to meet normal milestones.
The appearance of teeth may be delayed. These problems become more severe as the child ages. Growth failure in terms of body length is noted very early. Destruction of the thyroid in the fetus may occur if the mother is treated with radioactive iodine for thyroid cancer while she is pregnant . Radioiodine should be avoided unless the procedure is lifesaving.