What is congenital hypothyroidism?

The thyroid is a small, bow tie shaped gland, sitting in front of the neck just below the Adam's apple. It produces a hormone that plays an important part in regulating the body's metabolism and organ function, and it influences every organ, tissue and cell in the body. The thyroid hormone, thyroxine/T4, is in turn produced under stimulation from the thyroid-stimulating hormone/TSH - generated by the pituitary gland at the base of the brain.

How is the condition diagnosed?

Babies are screened in the first days of life for a variety of conditions. The heel prick or Guthrie test (where a small drop of blood is taken for testing) is usually performed by the midwife in the first 24 to 72 hours after birth.

Since the early 1980s thyroid screening has been included within this test. The lab can identify either a low thyroxine/T4 level - or a high thyroid stimulating hormone/TSH level (presence of either can indicate a poorly functioning thyroid gland).

Screening tests can sometimes be confusing, and infantile hypothyroidism can still develop even when the test is normal. In these cases, there may be a repeat test, using a small sample of vein blood. Sometimes your doctor will order X-rays of the baby's legs to show the bone ends at the knee joints. These can show immature appearances in babies who have hypothyroidism, and helps to confirm a diagnosis.

Are there any obvious signs of congenital hypothyroidism?

Infants with this thyroid gland abnormality will either appear to be quite normal at birth or will have such subtle features that the new parents won't be aware of a potentially serious problem.

Certain factors could indicate a possibility of hypothyroidism, and these will be taken into account during the clinical assessment by health care workers:

• Prolonged gestation of more than 42 weeks
  
• Birth weight above the 90th centile, despite a normal birth length and head circumference
  
• Delayed first stooling after birth
  
• Poor feeding due to lethargy and decreased appetite
  
• Prolonged jaundice resulting from secondary immaturity of the liver function - which is influenced, in turn, by thyroid function