It is a condition in which the thyroid gland does not produce enough thyroid hormone to meet the body's needs. About one in 4,000 newborn babies is born with hypothyroidism.

The thyroid is a small, butter-fly shaped gland located in the front of the neck. It uses iodine from the food we eat to make thyroid hormone, also called thyroxine or "T4". Thyroid hormone plays a vital role in normal growth and development. If the thyroid gland does not develop properly, it will not produce enough T4 for normal body growth and brain development.

Like most other glands that make hormones in the body, the thyroid is under the control of the pituitary, or "master gland," located at the base of the brain. If the amount of T4 in the body is too low, the pituitary senses it and releases a hormone, thyroid-stimulating hormone (TSH). The TSH stimulates the normal thyroid gland to produce more T4. When the thyroid gland produces enough T4 for the body's needs, no extra stimulation is needed, and the TSH level drops to the usual low level. In most hypothyroid babies, the thyroid gland has not developed properly and cannot produce enough T4. Consequently, the pituitary works very hard to stimulate the thyroid gland by producing high levels of TSH. As a result, these babies have a low T4 and a high TSH level.

The most common cause would be improper growth of the gland. During early pregnancy development of the thyroid gland begins to form at the base of the brain and then moves to the lower neck where it finishes growing. Sometimes the process is interrupted, leaving only a small piece of thyroid which may be in an abnormal location. Some babies will have no thyroid gland at all. Less common causes of hypothyroidism, include lack of stimulation by the pituitary gland or an inability of the thyroid gland to properly make thyroid hormone. All these causes result in a lack of the thyroid hormone which the baby needs. They are permanent conditions which the baby will not "grow out of."

Many family members with hypothyroid infants have other family members with thyroid problems. However, no clear pattern of inheritance appears to exist. There are some very rare types of inherited hypothyroidism. Your doctor will let you know if your baby's hypothyroidism is inherited.

About one in every 4,000 babies is born with hypothyroidism. The likelihood of having another baby with hypothyroidism is only slightly higher than the one in 4,000 chance. The chances are greater if your infant has one of the rare inherited forms of hypothyroidism. There is currently no reliable way of detecting hypothyroidism before birth.

The causes of an absent gland, an incompletely developed gland, or an abnormally positioned gland are not known. Many parents think that it is caused by something they did or didn't do during pregnancy. This is not true!

A few days after your baby was born, blood was taken from their heel. The blood sample was collected inside four circles on a piece of filter paper and sent to a newborn screening laboratory. At the lab, the blood levels of thyroid hormone (T4) and TSH were measured and one or both were found to be abnormal.

Sometimes the screening tests are so abnormal that we can be almost certain that a problem exists. A thyroid problem is unlikely if the screening tests results are borderline. Either way, screening tests need to be confirmed by further testing, both to see if hypothyroidism is present as well as to determine the cause.

Your baby's doctor may consult with or send you to a pediatric endocrinologist. The pediatric endocrinologist is a children's doctor who specializes in hormone problems such as hypothyroidism. A repeat measurement of T4 and TSH will be done on blood drawn from a vein. This is done to confirm the diagnosis of hypothyroidism. Several other tests may be done to check whether the baby has the normal amount of thyroid tissue, where it is located, and how well it makes thyroid hormone. These tests may include:

Thyroid uptake and scan – This test requires special equipment and special substances called radioactive iodine isotopes which are available at most larger hospitals. The radioactive material is dissolved in a small amount of liquid which can be swallowed or injected into a blood vessel. The amount of radioactivity in this dose is minimal, even less than an X-ray. After several hours a machine is used to "scan" the neck. If thyroid tissue is present, it will usually shine brightly on the scan. The amount of thyroid activity in the gland is often helpful in showing how well the gland is working.

Bone age: An X-ray of the knee or hand helps to determine skeletal maturity, which can be delayed in babies with hypothyroidism.

TRH Stimulation Test: In certain babies who have low T4 and low or only slightly raised TSH levels, a special test may be done to see if the pituitary gland produces the normal amount of TSH. A needle is placed in a vein, and a very small amount of thyrotropin releasing hormone (TRH) is given by vein. TRH normally stimulates the pituitary gland to make TSH. Several blood samples are drawn through the needle every 15-30 minutes for one hour.

Not all of these tests are necessary in most babies and there may be other tests which can be helpful in special cases. Your doctors will choose the tests needed after they talk with you and examine your baby. These tests can be done within a few days so that treatment can be started promptly if needed.

The effects of hypothyroidism are seen in different ways in different babies. The most noticeable effects usually involve:

• Skin – In some hypothyroid babies, newborn jaundice (a yellow tinge to the skin) may persist longer than usual. The baby's skin may be pale or blotchy, especially when undressed.
• Appetite and Digestion – The hypothyroid baby may be uninterested in taking the breast or bottle, and may be difficult to keep awake during feedings. They may be severely constipated and may hold on to gas in the stomach.
• Growth – Hypothyroid babies are often large as newborn infants. If their hypothyroidism is not corrected, they generally have poor growth and poor weight gain after birth.
• Circulation – Babies with hypothyroidism may have a slow heart rate and low blood pressure. The hands and feet may be cool to the touch due to poor circulation.
• Activity and Development – Babies with hypothyroidism are often quiet and seldom cry. They may seem uninterested in the sights and sounds around them. They may sleep for many hours and often have to be awakened to feed. They may feel "floppy" when they are picked up.

Starting a hypothyroid baby on treatment as soon as possible after birth is aimed at preventing permanent brain damage and intellectual disabilities. The effect of hypothyroidism on your baby's mental development is difficult to predict for several reasons. First, even hypothyroid babies may have a small amount of T4 which may be adequate for normal brain development. Second, a hypothyroid baby whose development is slow at first may catch up in the months after proper thyroid replacement is started. Finally, mental development in all babies is affected by inheritance and environment. As a rule, the earlier treatment is started, the better the chance a baby has of reaching their full mental development potential.

The treatment is daily replacement of the missing thyroid hormone with synthetic thyroid hormone tablets (also called sodium levothyroxine or L-thyroxine). The synthetic thyroid hormone acts exactly like the hormone produced by the thyroid gland. When given at the proper dosage, there are no side effects from taking synthetic thyroid hormone.

L-thyroxine tablets are available in many strengths. Your doctor will start your baby on therapy with one of the lower strength tablets and will increase the dosage as your child grows. They will decide when your child needs a higher dosage of thyroid hormone by examining your child and measuring blood levels of T4 and TSH at regular intervals.

Thyroid hormone tablets are very small. They can be crushed and dissolved in a teaspoon of breastmilk, juice, or water. You can give the tablet-liquid solution through a dropper or a small syringe. When the baby begins taking solid foods, you can mix the crushed tablet with a teaspoon of cereal or strained fruit. Older babies can simply chew and swallow the tablet. Do not mix the crushed thyroid tablet into a bottle of formula or other liquid, because the full dose will not be taken if your baby does not finish the bottle.

Fortunately, no. The tablets have very little flavor of their own.

For the rest of their life. Thyroid hormone is especially important for brain development in the first two years of life. It is also necessary for body growth and development and the normal function of all the body's systems. Stopping thyroid hormone replacement in adulthood can lead to sluggishness, weight gain, constipation, puffiness and dry skin. For these reasons, thyroid must be taken every day for the entire life.

Giving your child's thyroid replacement will soon become part of your daily routine. Many people keep a calendar on which they check off the date every morning after giving the tablet. Other people find it helpful to count out seven tablets at the beginning of every week and place them in a separate container. Try to avoid missing a dose.

No. Your child can take any medications prescribed by your doctor. They should also receive immunizations just as any other child would.

No! Too much thyroid hormone will speed up the body's functions to a dangerous level, causing a fast heart rate, diarrhea, difficulty sleeping and shakiness. Giving more thyroid hormone than is recommended will not make your baby smarter.

This depends on how the lack of thyroid hormone has affected your baby before treatment. If the baby showed very few signs of hypothyroidism before treatment, they may change very little after treatment is started. The earliest changes, which occur four to five days after treatment is started, include:

Increased Urinations – Your baby will begin to get rid of the excess "water weight" and will begin to lose their puffy appearance.

Increased Activity – Your baby may begin to spend less time sleeping and more time crying. They may demand more attention. This is a good sign. It shows that your baby has more interest in the environment than they had before treatment.

Increased Appetite – You may notice an improvement in your baby's appetite. They may cry to be nursed more often, and may feed more vigorously.

Change in Appearance – Your baby's skin color may improve after the first few weeks of treatment. They will begin to appear more mature and generally more healthier.

New Skills – If your baby's development has been slow, they should begin to gain new skills more quickly after thyroid hormone replacement is started.

As long as thyroid hormone pills are taken regularly, babies with congenital hypothyroidism usually show perfectly normal growth and development and can enter any adult occupation and have a family. Except for the continuing need to take thyroid hormone, your baby has the same outlook in life as does any other baby. If your baby was born with any problems besides hypothyroidism, the effect of these should be discussed with your doctor.