What is congenital hypothyroidism?

Hypothyroidism is a condition resulting from an under-active thyroid gland that does not produce enough thyroid hormone for the body’s needs. The term ‘congenital’ means that the condition is present at birth.

What is the thyroid gland and what does it do?

The thyroid gland is situated in the lower part of the neck, just below the Adam’s apple, and produces several hormones including thyroxine (T4). Thyroxine is essential in children for the normal growth of the body and for the brain to develop normally. Normal amounts of thyroxine are especially important during the first few months of life when the brain is developing very quickly.

What causes congenital hypothyroidism and is it inherited?

Very early in an unborn baby's development the thyroid gland moves from the back of the tongue to its normal position in the neck. In some babies this fails to occur and the gland does not develop at all. In others it is higher in the neck than normal and does not work as well. These are the most common situations in a child with congenital hypothyroidism. Normally the risk of having another child with congenital hypothyroidism is very low. There is, however, a rarer type where the gland is in the right position but does not produce thyroxine normally. This type can be inherited and there is a risk that the baby’s siblings will also be affected.

Is there anything I did during pregnancy which made my child hypothyroid?

No. In most cases the cause is currently not known and there is no way to prevent it.

How common is congenital hypothyroidism?

One child in every 3,500-4,000 is born with hypothyroidism in the UK. It is more common in girls than in boys.

What are the symptoms of congenital hypothyroidism?

Over half the babies born with congenital hypothyroidism look entirely normal and have no symptoms at all. That is why it is so important that all children are tested at birth. Congenital hypothyroidism can often be diagnosed before the baby shows any definite signs of the condition.

Some babies with hypothyroidism are sleepy and difficult to feed, but a blood test is needed to be sure of the diagnosis. Lots of babies have these symptoms without being hypothyroid! Other symptoms may include constipation, low muscle tone (floppiness), cold extremities, and poor growth. Some hypothyroid babies have prolonged jaundice after birth. Although some children with congenital hypothyroidism have development problems, the likelihood of long-lasting effects is low. If your child is diagnosed with congenital hypothyroidism the doctor will examine them very carefully to check for any other problems.

Why are babies screened for hypothyroidism?

Untreated, congenital hypothyroidism can result in impaired neurological development of the child. In the past, hypothyroid children were often not started on treatment until they were several months old. As a consequence, some had learning difficulties or mild clumsiness. They would almost certainly have benefited from early treatment. We now know that if thyroid hormone treatment can be started before the baby is about two weeks old a decrease in IQ (Intelligence Quotient) can be avoided.

How are babies screened for hypothyroidism?

Every baby should be checked for hypothyroidism soon after birth. Screening is performed at about four to five days old with a heelprick blood test. A small amount of blood from the baby’s heel is placed on a filter paper and sent to a regional laboratory to test for TSH (thyroid-stimulating hormone). If the TSH is high and therefore suggestive of hypothyroidism, the diagnosis is checked by testing a small blood sample taken from a vein.

What is the treatment for congenital hypothyroidism?

If your baby tests positive, his or her condition should be managed by a paediatric endocrinologist or a paediatrician with a special interest in endocrinology (hormone specialist who deals with children) and treatment with levothyroxine (synthetic thyroid hormone) should be started without delay. The dose is carefully calculated based on factors such as the weight of the baby, and will need adjusting regularly as the baby grows. The adjustment is monitored with blood tests of thyroid hormone and TSH. These tests are carried out every two to three months during the first year of life and every three to six months during infancy and childhood.

Levothyroxine is usually prescribed in tablet form. Giving levothyroxine to infants can be a challenge, but if the tablet is crushed it can be given in liquid (water, milk, or formula). You should not, however, add the crushed tablet to your baby’s feeding bottle as it is important the baby gets the whole dose. Mix the crushed tablet with the liquid and give it on a spoon or with a medicine dispenser pipette. Do not give your baby a full feed immediately after giving the levothyroxine in case the baby ‘throws up’ part of this feed and loses some of the dose. Once your child is old enough to drink from a cup or beaker, you can give the tablets along with a drink of water. A liquid form of levothyroxine - Evotrox - is now available in the UK.

Are there any side effects of treatment?

Treatment with levothyroxine simply replaces the thyroxine that the thyroid gland is unable to make. It is very effective and it is usually fairly easy to give the correct dose. If too much levothyroxine is given it may cause symptoms of hyperthyroidism such as restlessness, mild diarrhoea, poor weight gain and rapid growth. Too little levothyroxine may cause symptoms of hypothyroidism such as less energy, constipation, cold extremities, or unexpected weight gain and slow growth. IQ levels may also be affected if T4 levels are low. Over-treatment or under-treatment should not happen if blood tests are carried out at regular intervals.

What about the longer term?

Your child will usually need to take levothyroxine tablets for life but this should present no great problems as levothyroxine is widely available, is currently free of prescription charges, and needs to be given only once a day. After starting treatment your child should be tested regularly (every one to two months in the first year and every three to six months throughout infancy and childhood) and you should ensure that the medication is taken regularly.

What happens if I forget a dose?

It is important to take the tablets regularly and on the same schedule. A missed dose is not a catastrophe as levothyroxine lasts in the body for several days, but obviously it is important for your child’s health that this does not happen often. If you forget a dose do not double up but take the prescribed daily dose the next day.

Will my child have a normal life when he or she grows up?

The vast majority of children who have been screened at birth and diagnosed and treated from an early age will grow up normally. Your child has an excellent chance of a normal childhood, going to a normal school and living a normal independent life as an adult. Screening for congenital hypothyroidism at birth and starting treatment if the test is positive means that a low IQ and other development problems can be avoided.

Some important points….

  • The heelprick test in newborn babies has vastly improved the prospects for babies born with hypothyroidism
  • The vast majority of children who are detected and treated promptly grow up normally
  • Babies and children with hypothyroidism should be seen regularly by a paediatrician or a paediatric endocrinologist
  • Medication must be taken regularly and usually for life
  • The dose will be adjusted as your child grows and so regular blood tests are important
  • Check with your doctor whether your child’s prescription is exempt from charges

It is well recognised that thyroid problems often run in families and if family members are unwell they should be encouraged to discuss with their own GP whether thyroid testing is warranted.

If you have questions or concerns about your thyroid disorder, you should talk to your doctor or specialist as they will be best placed to advise you. You may of course contact the British Thyroid Foundation for further information and support, or if you have any comments about the information contained in this leaflet.


First issued: February 2008. Revised October 2011. Our literature is reviewed every two years and revised if necessary.