Congenital hypothyroidism

Newborn babies who are unable to make enough thyroid hormone have congenital hypothyroidism. Thyroid hormone is essential for brain development. If the condition is not found or left untreated, it can result in irreversible neurological problems and poor growth. However, if this hormone deficiency is treated within 2-3 weeks after birth, permanent brain damage can be avoided.  

In Belgium, about 1 in every 2,000 to 3,000 newborns has congenital hypothyroidism, which is about 30 to 40 babies per year. It is twice as common in girls as in boys. 

In most cases, the condition is permanent, and the child will need lifelong treatment.  

There are several causes of thyroid hormone deficiency at birth. 

The most common cause is a thyroid gland development or migration disorder in the foetus: 

• The thyroid gland is not located in the right place 
• The thyroid gland is underdeveloped and very small 
• There is no thyroid gland 

Parents and siblings have up to 10-20 times more thyroid problems than individuals in the general population.  

Other causes include: 

• Defective thyroid hormone production (15%) 

The thyroid gland does not produce enough hormone, because one of the required components (e.g. enzymes) for this is missing. These forms of hypothyroidism are more hereditary than thyroid gland developmental disorders and generally have a 25% recurrence rate (1 in 4 for each child). The parents usually have one normal gene and therefore no thyroid problems. 

• Problems with the pituitary gland  

The pituitary gland does not produce thyroid stimulating hormone (TSH), which tells the thyroid to make thyroid hormone 

• Transient hypothyroidism, for example due to anti-thyroid medication or iodine taken by the mother during pregnancy 

In Belgium, thyroid gland function is tested in every newborn as part of standard screening. On the 3rd to 5th day of life, a few drops of blood (taken by heel puncture or via a normal blood sample) are placed on a card for laboratory analysis. The lab checks the levels of:  

• Thyroxine (T4), one of the thyroid hormones 
• Thyroid-stimulating hormone (TSH), a hormone produced by the pituitary gland that tells the thyroid gland to make thyroid hormone 

A blood sample will be taken from the vein to confirm any diagnosis. This test will check whether thyroxine and TSH levels are within the normal range. Other tests that may be performed include an X-ray of the knee and thyroid scans. 

Newborns with congenital hypothyroidism that is not detected by the heel prick (less than 2% in Belgium) develop the classic symptoms of a thyroid hormone deficiency (hypothyroidism) in the first weeks of life: 

• Prolonged yellowing of the skin and eyes 
• Low muscle tone with a weak sucking reflex (slow feeding) 
• Little activity (sleepiness) 
• Constipation 
• Weak Achilles tendon reflex 
• Umbilical hernia (“outpouching” of the belly button) 
• Thick tongue 
• Low temperature, cold skin 
• Large anterior and posterior fontanelle (large soft spots of the skull) 
• Slow heartbeat 

Congenital hypothyroidism is treated by administering the missing thyroid hormone thyroxine (T4) by mouth. Treatment should be started as soon as possible to prevent permanent brain damage (low IQ).  

It is very important that the medication (levothyroxine) is taken properly, that the dose is properly adjusted and that blood levels of thyroid hormone and TSH are measured regularly. 

The goal is to have blood thyroxine levels in the high to normal range and TSH levels that are normal for the infant’s age. If the medication is not taken properly during the first 3 years of life, there is a high risk of permanent brain damage and low IQ. 

If it is not certain whether the thyroid hormone deficiency is permanent, treatment can be interrupted or reduced after the age of 3 years and a blood test performed after 4-6 weeks.