CH can be the result of a number of different underlying causes. Missing or misplaced thyroid gland: Most babies with CH are missing their thyroid gland or have a thyroid that did not develop properly. In some cases, the thyroid gland may be smaller than usual or may not be located in the correct place. In healthy people, the thyroid gland is located in the center of the front of the neck, near the top of the windpipe. In some children with CH, the thyroid gland may instead be under the tongue or on the side of the neck. If the thyroid gland is in the wrong place, or if it is underdeveloped, it often does not work well and makes less thyroid hormone than needed by the body. If the thyroid gland is missing, the baby cannot make any of its own thyroid hormone. A missing, underdeveloped or misplaced thyroid gland is a birth defect that happens for unknown reasons and is usually not inherited.
Hereditary causes: Less often, CH is caused by inherited changes in a gene or pair of genes. This is explained in more detail below. Children with the inherited type of CH do not make enough thyroid hormone even though their thyroid gland appears normal in size and shape. About 15% of children with CH are thought to have an inherited form. Maternal iodine deficiency: If the mother is deficient in iodine during the pregnancy, the fetal thyroid gland may not be able to make enough thyroid hormone. The baby is then born with CH. This is a problem in some parts of the world where people do not get enough iodine in their diet.
Maternal thyroid condition and medications: In a small number of cases, CH occurs when the mother is given anti-thyroid drugs during pregnancy to treat her own thyroid problem.