Hypothyroidism occurs when the thyroid gland does not produce enough thyroid hormone, which can result in a slower metabolism. In children this can mean slower growth, unintentional weight gain, and feeling tired often. Hypothyroidism can occur in about 1 out of every 4,000 to 5,000 babies born.

Hypothyroidism can be the result of a congenital disorder, meaning it is present from birth. It is known as an endocrine disorder, the result of a hormone imbalance. Anyone can get hypothyroidism, but it is more common in people assigned female at birth (AFAB) over the age of 60, or if you have other conditions, such as a history of thyroid surgery, pregnancy, previous head/neck radiation therapy, or starting or stopping certain medications. It can also occur later in some children as the result of an autoimmune disorder.

Hypothyroidism leads to a decreased rate of growth causing lower than average height. As thyroid hormone is lacking, this can slow many processes within the body, potentially leading to slow heart rate, fatigue or exercise intolerance, slower reaction time, weight gain, sparse hair growth, coarse, dry and thickened skin, cold intolerance, muscle cramps, hoarse voice, dull facial expression, slow speech, droopy eyelids, puffy and swollen face, sides of eyebrows thin or falling out, enlarged thyroid with a goiter-like growth on the neck, increased menstrual flow in girls and women, and slow bowel movements.

Hypothyroidism present at birth is usually picked up during routine assessments; however, it can occur later in some children as the result of an autoimmune disorder, improper development, removal or damage of the thyroid gland, or when the brain does not make thyroid-simulating hormone (TSH). Hypothyroidism is usually diagnosed with a blood test to test for levels of thyroid hormone.