A poorly functioning pituitary gland may also cause a lack of thyroid hormone, leading to central hypothyroidism. Thyroid hormone is critical for growth and brain development, especially during the first few weeks to months of life. Children with untreated hypothyroidism are at high risk of mental retardation; thus, early detection is crucial. Central hypothyroidism can be diagnosed by a low or normal thyroid-stimulating hormone (TSH) in the presence of a low level of free T4. Free T-4 should be checked annually for at least four years.