Revised 2015

What is congenital hypothyroidism?

Congenital hypothyroidism (CHT) is a condition resulting from an absent or under-developed thyroid gland (dysgenesis) or one that has developed but cannot make thyroid hormone because of a ‘production line’ problem (dyshormonogenesis). Babies with CHT cannot 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. It produces the two key hormones thyroxine (T4) and tri-iodothyronine (T3). Thyroid hormone is essential for normal growth in childhood and adolescence and essential for brain development in infancy.

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 as it should. Dysgenesis is the term that is often used to describe these forms of CHT. Around 80% of babies with CHT have dysgenesis and the risk of a couple having another child with this kind of CHT is low. The more uncommon type, dyshormonogenesis, affects around 20% of babies with CHT. The gland is in the right position but does not produce thyroxine normally because of a ‘production line’ problem. 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. Dysgenesis is more common in girls than in boys but in dyshormonogenesis boys and girls are equally affected.

What are the symptoms of congenital hypothyroidism?

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

Some babies with hypothyroidism are sleepy and difficult to feed, although lots of babies have these symptoms without being hypothyroid! This really highlights the importance of screening for CHT in all newborn babies. Other symptoms may include constipation, low muscle tone (floppiness), cold extremities, and poor growth. Some hypothyroid babies have prolonged jaundice (with an associated yellow skin) after birth. Although some children with CHT have development problems, the likelihood of a significant long-lasting effect is low as long as appropriate treatment is started promptly. If your child is diagnosed with CHT the doctor will examine them very carefully to check for any other problems.

Why are babies screened for hypothyroidism?

Untreated, CHT can result in impaired brain development. 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. We now know that if thyroid hormone treatment can be started before the baby is about two to three weeks old a decrease in intelligence quotient (IQ) can be avoided in most babies.

How are babies screened for hypothyroidism?

Every baby should be checked for hypothyroidism soon after birth. Screening is performed at about five days of age with a heel-prick 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). TSH is produced by the brain and tells the thyroid gland to work. Levels will be high if the brain is telling the thyroid gland to work but it isn’t responding in the normal way. 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, T4) should be started without delay. You only need to treat with T4 (rather than T3) in newborn babies because the body can use the T4 to make T3. 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 by blood tests that measure thyroid hormone and TSH levels. These tests are carried out every few weeks 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, breast or formula milk). You should not, however, add the crushed tablet to your baby’s feeding bottle as they may not drink it all. 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 vomits 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.

Are there any side effects of treatment?

Treatment with levothyroxine simply replaces the thyroxine that the thyroid gland is unable to make. Hence treatment is putting back what nature is not making. 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 an over-active thyroid (hyperthyroidism) such as restlessness, mild diarrhoea, poor weight gain and rapid growth. Too little levothyroxine may cause symptoms of an under-active thyroid (hypothyroidism) such as lethargy, constipation, cold extremities, or unexpected weight gain and slow growth. Significant periods of 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 few weeks in the first year, every three to six months throughout infancy and childhood and every six to 12 months in adult life) 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.

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 CHT at birth and starting treatment if the test is positive means that a low IQ and other development problems can be avoided. It is possible that there may be very subtle long term changes in some babies who have very low thyroid hormone levels in early life and this is an area that requires more research.

Some important points….

  • The heel-prick 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 paediatric endocrinologist or a paediatrician with a special interest in endocrinology
  • Medication must be taken regularly and usually for life
  • The dose will need to 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 also contact the British Thyroid Foundation for further information and support, or if you have any comments about the information contained in this leaflet.

The British Thyroid Foundation

www.btf-thyroid.org
The British Thyroid Foundation is a registered charity: England and Wales No 1006391, Scotland SC046037

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Endorsed by:

The British Thyroid Association - medical professionals encouraging the highest standards in patient care and research
www.british-thyroid-association.org

The British Association of Endocrine and Thyroid Surgeons - the representative body of British surgeons who have a specialist interest in surgery of the endocrine glands (thyroid, parathyroid and adrenal)
www.baets.org.uk

First issued: 2008
Revised: 2011, 2015
Our literature is reviewed every two years and revised if necessary.
© 2015 BRITISH THYROID FOUNDATION

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