How to Give Levothyroxine to Your Baby

However, pregnant women in the United States can develop mild iodine deficiency because theirbodies need more iodine when they are pregnant. Children whose diet is restricted because they have multiple food allergies or who are fed through a tube inserted into a vein (parenteral nutrition) may not eat enough of the proper foods and thus develop iodine deficiency. For both forms of hypothyroidism, the dose is titrated to maintain serum T4 and TSH levels within the normal range for age.

Etiology of Hypothyroidism in Infants and Children

Hypothyroidism also occurs as a result oftreatment for hyperthyroidism or for thyroid cancer. Congenital hypothyroidism occurs when the thyroid gland does not develop or function normally before birth. In acquired hypothyroidism, the usual starting dose of levothyroxine often depends on degree of hypothyroidism at diagnosis. For severe, longstanding hypothyroidism, lower starting doses may be selected to avoid potential behavioral symptoms with slower titration to full dosing. Thyroid ultrasonography is not necessary to establish the diagnosis of autoimmune thyroiditis and should be restricted to children with thyroid gland asymmetry or palpable thyroid nodules.

• Children with other genetic conditions (eg, DiGeorge syndrome, Prader-Willi syndrome) are at increased risk of acquired hypothyroidism that is not autoimmune.
• Reverse T3 levels measure the metabolically inactive form of T3; reverse T3 increases during periods of illness or starvation and should not be measured to diagnose hypothyroidism.
• Babies and older children also need thyroid hormone for normal growth, among other important body functions.
• For children with euthyroid sick syndrome, thyroid function normalizes as the clinical status improves.
• Biotin is a common over-the-counter supplement that can interfere with thyroid function tests by causing false readings of certain hormones.

Diagnosis of Hypothyroidism in Infants and Children

If the screening is positive, tests to determine levels of synthroid hungrier thyroid hormones in the blood (thyroid function tests) are done to confirm the diagnosis of hypothyroidism. If confirmed, newborns must be treated quickly to prevent developmental delays. In another rare cause, the pituitary gland is abnormally formed and fails to stimulate the thyroid gland to produce thyroid hormones. This pattern of thyroid abnormality also can develop in children who take certain medications (such as antiseizure medications and medications that help the body recognize and attack cancer cells) or who have certain illnesses.

• Diagnosis is by thyroid function testing (eg, serum thyroxine, thyroid-stimulating hormone).
• Iodine deficiency remains the most common worldwide cause of hypothyroidism in children but is rare in the United States.
• You do not need to worry about thyroid hormones interacting with other medications, as the medicine simply replaces a hormone that your child is no longer able to make.
• The absorption oflevothyroxine may be decreased if it is given with soy formula, iron, or calcium.

What is Thyroid Hormone?

Symptoms in infants include poor feeding and growth failure; symptoms in older children and adolescents are similar to those of adults but also include growth failure, delayed puberty, or both. Diagnosis is by thyroid function testing (eg, serum thyroxine, thyroid-stimulating hormone). Thyroid function tests are also done in older children and adolescents who doctors think may have hypothyroidism. Biotin is a common over-the-counter supplement that can interfere with thyroid function tests by causing false readings of certain hormones. Ultrasonography may also be done in older children and adolescents if the thyroid gland feels asymmetric or the doctor feels a growth (nodule) on the thyroid gland. Older children who have only slight elevations in TSH (typically between 5 mU/L and 10 mU/L) and normal free T4 levels are considered to have subclinical hypothyroidism.

• Permanent hypothyroidism is also the goal of therapy for patients undergoing definitive therapy for Graves disease (see treatment of hyperthyroidism in infants and children) or thyroid cancer.
• Children who have Down syndrome or Turner syndrome are at increased risk of Hashimoto thyroiditis.
• Free T4 is a better measure of thyroid function than total T4 in these patients because the levels of thyroid-binding proteins (thyroid-binding globulin, transthyretin, and albumin) affect total T4 levels.
• Eventually, infants may develop dry, cool, mottled skin, coarse facial features (such as a flat, broad nasal bridge and a puffy face), and a slightly open mouth with an enlarged tongue.
• Once newborns no longer receive thyroid hormone from their mother, symptoms develop slowly and the disorder is detected only when they undergo newborn screening tests.

The rare side effects of thyroid hormone medication are related to overdose, or too much medication, and can include rapid heart rate, sweating, anxiety, and tremors. If your child experiences these signs and symptoms, you should contact the physician who prescribed the medication for your child. A child will not have these problems if the thyroid hormone dose prescribed is only slightly more than is needed. Worldwide, the most common cause of hypothyroidism is iodine deficiency, but this cause is rare in the United States.

Another rare cause is central hypothyroidism, which is caused by structural anomalies in pituitary development; patients usually also have other pituitary hormone deficiencies. Signs specific to children are growth retardation, delayed skeletal maturation, and usually delayed puberty. Autoimmune thyroiditis occurs most commonly during adolescence, but it also occurs in younger children, typically after the first few years of life. Children with trisomy 21 and Turner syndrome are at increased risk of autoimmune thyroid disease. Children with other genetic conditions (eg, DiGeorge syndrome, Prader-Willi syndrome) are at increased risk of acquired hypothyroidism that is not autoimmune.

At first, newborns who have hypothyroidism that is caused by a problem with their thyroid gland usually have few if any symptoms because some thyroid hormone from the mother crosses the placenta. Once newborns no longer receive thyroid hormone from their mother, symptoms develop slowly and the disorder is detected only when they undergo newborn screening tests. Most children who have congenital hypothyroidism usually need to take thyroid hormone replacement for life. However, some children who have congenital hypothyroidism, usually those who have not required a dose increase after infancy, may be able to stop treatment after they are about 3 years of age. In congenital hypothyroidism,treatment with levothyroxine orally once a day must be started immediately and be closely monitored.

Symptoms that do occur may be subtle or develop slowly because some maternal thyroid hormone crosses the placenta. Rarely, delayed diagnosis and treatment of severe hypothyroidism lead to intellectual disability and short stature. Permanent hypothyroidism is also the goal of therapy for patients undergoing definitive therapy for Graves disease (see treatment of hyperthyroidism in infants and children) or thyroid cancer. Rarely in the United States but commonly in countries where iodine is not routinely added to table salt, hypothyroidism results from maternal iodine deficiency. Rarely, transplacental transfer of antibodies, goitrogens (eg, amiodarone), or antithyroid medications (eg, propylthiouracil, methimazole) causes transient hypothyroidism.

Symptoms that appear only in children include slowed growth, a delay in the development of the skeleton, and delayed puberty. Older children can be monitored more frequently if there are concerns about adherence. After a dose adjustment in older children, TSH and free T4 levels are measured in 6 to 8 weeks. Most other hypothyroid infants initially have few if any symptoms or signs and are detected only through newborn screening. Most newborns who are treated have normal movement control and intellectual development. Hormones are chemical messengers that affect the activity of another part of the body.

Iodine deficiency remains the most common worldwide cause of hypothyroidism in children but is rare in the United States. Iodine deficiency may occur in children whose diet is restricted because of multiple food allergies or in those who require long-term parenteral nutrition. Treatment of hypothyroidism is directed by a doctor who specializes in treating children with problems of the endocrine system (called a pediatric endocrinologist). Doctors continue to monitor children by doing blood tests at regular intervals depending on their age.