Congenital hypothyroidism

Congenital hypothyroidism is a disorder affecting the thyroid gland, which is in the neck. The thyroid gland produces a hormone (chemical substance) called thyroxine, which is needed for normal growth and development.

If the thyroid gland does not produce enough thyroxine, it causes hypothyroidism. If the disorder is present at birth, it is called congenital hypothyroidism.

In the UK, all babies are tested for congenital hypothyroidism soon after birth, using a tiny amount of blood taken from pricking their heel. If this test shows that the baby possibly has hypothyroidism, it will be recommended that he or she have further blood tests to confirm the diagnosis.

He or she will also have a special scan of the neck that allows doctors to see if the child's thyroid gland is present and in the right place (explained below). The scan is painless and uses a special intravenous marker that is only taken up by the thyroid gland. This is extremely useful information as it allows us to tell you whether there is a chance of the condition happening in another child that a parent might have.

For a very small number of children born with hypothyroidism, hearing problems can occur as part of a rare syndrome (collection of symptoms often seen together) or if there is severe hypothyroidism at birth.

For this reason, all young children coming to Great Ormond Street Hospital (GOSH) for diagnosis and treatment of congenital hypothyroidism will have a detailed hearing assessment at about six weeks of age. This will still need to be done even if the baby has passed the neonatal hearing assessment. Please remember that it is extremely rare for serious hearing problems to occur as a result of congenital hypothyroidism. However, it may still be necessary for your child to be monitored by the audiology department for some months.

Most babies with congenital hypothyroidism are diagnosed very early, before they have any symptoms. If these signs and symptoms are present, they may include feeding difficulties, sleepiness, constipation and jaundice (the skin may look yellow).

It is very important that the above tests are carried out soon after the heel prick blood tests are known. This is because if congenital hypothyroidism is not diagnosed and treated soon after birth, it can cause problems with mental development, learning and clumsiness.

During the early months of pregnancy, when your baby's organs are developing, the thyroid gland moves from the back of the tongue to its normal position in the neck. In some babies this does not happen, which means that the gland cannot work properly. On other occasions the thyroid gland does not develop at all. For parents with one child with this type of congenital hypothyroidism, the chance of having another baby who is affected is very low.

There is another very rare type of hypothyroidism in which a child's thyroid gland is in the right place, but it cannot produce thyroxine. This type is inherited and so there is a risk that if parents have another child in the future they may have the same condition. If you are worried, please ask to talk to a genetics nurse about this.

In the UK, around one in every 3500 newborn babies have congenital hypothyroidism. It is more common in girls than boys, but at the moment we do not understand why.

Congenital hypothyroidism is treated by replacing the thyroxine that the body cannot produce. This is usually in liquid form but tablets can also be used. The medicine only needs to be given once a day. Although missing an occasional dose will not cause any immediate problems, it is best to try and make sure that the child takes their medicine regularly each day and therefore keeps a steady level of thyroxine in their blood.

For the first couple of years, the child will need regular blood tests to check these levels. Doctors use the information from these tests to work out the right dose of thyroxine for the child, which changes as they gain weight and develop.

Once the child is two or three years old, they will need fewer blood tests as the dose of thyroxine will be calculated according to how he or she is growing. They will need to take thyroxine for the rest of their life, but this quickly becomes routine. The medicine is easily available and can be ordered on repeat prescription from the child's family doctor (GP).

Because thyroxine medicine is simply replacing a normal chemical produced by the body, giving the correct dose every day should not have any side effects. However, if given too little thyroxine, the child will develop the symptoms of hypothyroidism outlined earlier, and over a long period, may grow more slowly than usual. If the child has too much thyroxine, he or she may develop mild diarrhoea, not put on weight, may be more restless than usual and over a long period may grow more quickly than usual. But, as described above, the correct dose for the child will be calculated on a regular basis, so these effects are unlikely to occur.

It is difficult to predict whether any young child will grow up normally. However, screening for congenital hypothyroidism has been happening in the UK for long enough for us to know that almost all children who are diagnosed and treated from an early age will grow up normally.

However, a small proportion of children who have had severe hypothyroidism in the womb may have some difficulties later in life, like poor hearing, clumsiness or trouble with learning. These problems can be reduced if hypothyroidism is picked up early and treated as described above.