Revised 2018

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 thyroid hormone. This is mainly thyroxine (T4) with a small (10%) amount of tri-iodothyronine (T3). Thyroid hormone is essential for brain development in infancy and normal growth in childhood and adolescence.

What causes congenital hypothyroidism and is it inherited?

Thyroid gland development in a baby begins very early in pregnancy. The gland begins to form at the back of the tongue and moves to its normal position in the lower neck by eight weeks. In some babies the gland does not develop properly and/or may not move to the normal position. This form of CHT is called dysgenesis and a gland that is in the wrong position is called ectopic. The risk of having another child with this type of CHT is low.

In some cases, the thyroid gland develops and moves into the correct position but there is a problem with the thyroid hormone ‘production line’ and it has difficulty making thyroid hormone. This type of CHT is called dyshormonogenesis. It may occur if a baby has inherited a faulty CHT gene from mum and/or dad 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 2000-3000 is born with CHT 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?

Most babies born with CHT look entirely normal and have no obvious symptoms. That is why it is so important that all children are tested at birth. CHT is often 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. Some hypothyroid babies also have prolonged jaundice (with an associated yellow skin) after birth. Other later symptoms may include constipation, low muscle tone (floppiness), cold extremities, and poor growth. When appropriate treatment is started promptly children with CHT develop within normal limits in a way that is identical, or nearly identical, to unaffected siblings (brothers and sisters). 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, babies with hypothyroidism were often not diagnosed until they were several months old and started on treatment late. 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 the likelihood of significant long-lasting problems are low.

How are babies screened for hypothyroidism?

All babies have a heel-prick blood test at five days of age to screen for several conditions. One of these conditions is CHT and this is tested for by measuring a hormone called TSH (thyroid stimulating hormone). TSH is produced by the brain and is a messenger to tell the thyroid gland to make more thyroid hormone. If the thyroid hormone is low, the brain makes more TSH message to tell the thyroid to work even harder.

If the TSH is high on the heel-prick blood test, it suggests that the thyroid hormone is low and the baby will need to have a small blood sample taken from a vein to confirm the diagnosis.

What is the treatment for congenital hypothyroidism?

If your baby tests positive, his or her condition should be managed by a paediatric endocrinologist (a hormone specialist who deals with children) or a paediatrician with a special interest in endocrinology. Treatment with levothyroxine (synthetic thyroid hormone, T4) 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 by blood tests that measure thyroid hormone and TSH levels. These tests are carried out every few weeks during the first few months of life and around every two to six months during infancy and childhood. You must treat with T4 (rather than T3) in children because the brain requires T4 to develop well and the body makes T3 from the T4.

Levothyroxine is prescribed in tablets or a solution. Levothyroxine tablets can be crushed in 1oz (30ml) of liquid (water, breast or formula milk). The liquid can be given on a spoon or with a medicine dispenser pipette or pacifier. You should not add the levothyroxine to your baby’s full feeding bottle as they may not drink it all. Levothyroxine solution is made in three different strengths so always check that the bottles are the same and check with your pharmacist if unsure. It is quite sticky and you can also mix it in 1oz (30ml) of milk if your baby prefers this. Once your child is old enough to drink from a cup or beaker, you can give levothyroxine 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. Therefore treatment is putting back what the thyroid is not making enough of. 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 overactive thyroid (hyperthyroidism) such as restlessness, mild diarrhoea, poor weight gain, poor sleep and rapid growth. Too little levothyroxine may cause symptoms of an underactive thyroid (hypothyroidism) such as lethargy, constipation, cold extremities, or unexpected weight gain and slow growth. Lengthy periods of over-treatment or under-treatment should not happen if blood tests are carried out at regular intervals and you attend regular reviews of your child’s progress.

What about the longer term?

Your child will usually need to take levothyroxine 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 few months of life and 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 ideally at the same time each day. A single missed dose is not a dangerous as levothyroxine lasts in the body for several days, but 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 with CHT have been screened at birth and treated from an early age and 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

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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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, 2018
Our literature is reviewed every two years and revised if necessary.
© 2018 BRITISH THYROID FOUNDATION

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