TSH is the abbreviation for thyroid stimulating hormone. TSH is a hormone that your pituitary gland produces; the production of TSH sets off a chain reaction and lets your thyroid know it's time to make its own hormones, called T3 and T4. The thyroid and pituitary glands are responsible for overseeing all of your hormone levels, as well as respiration rate, body temperature, metabolism and other vital functions. Infants' TSH levels must be regulated in order to keep them healthy and developing properly.
TSH levels are measured during an infant's first few days of life through a blood draw, according to the American Family Physician. Due to the mother's thyroid hormones crossing the placenta, it may not be immediately apparent if your baby's TSH is in the normal range just after birth. Your newborn may have another series of blood tests between the ages of 2 and 6 weeks to confirm the readings; his TSH level in this age range should be between 1.7 and 9.1 milliunits per liter--mU/L
High levels of TSH in an infant generally points to congenital hypothyroidism, a condition that can have dire consequences if not treated swiftly, according to the American Family Physician. Congenital means the baby was born with the condition; hypothyroidism is a condition in which the body does not make enough thyroid hormone, which is indicated by a high TSH test of 40 mU/L. Congenital hypothyroidism that goes untreated for the first few weeks of an infant's life can lead to mental retardation.
Other factors that can possible create higher-than-normal TSH readings in older babies who are not diagnosed with congenital thyroid disease, are environmental toxins. Environmental Health News reported in July 2010 that three different chemicals that are present in water, some foods and tobacco smoke, can inhibit the production of thyroid hormones, thus causing TSH levels to become elevated. The chemicals, thiocyanate, perchlorate, and nitrate, can contaminate drinking water and therefore become an unwanted, yet added ingredient in baby formula that is mixed with drinking water, breastmilk produced by mothers who drink the water, and babies who drink water themselves.
Low TSH usually means that you have an overactive thyroid, or your body makes too much thyroid hormone. Medline, a service of the National Institutes of Health, explains that low levels of TSH may also be the result of taking medications, but these situations are unlikely in infants. American Family Physician reports that infants with low or a delayed-rise of TSH tend to be babies who were born early, at low birth weight, or suffer from an underlying illness.