When a baby is low on thyroid hormones

Thyroid hormone levels are part of the usual newborn screening process in Malaysia, as congenital hypothyroidism is the most common preventable cause of mental disability in children. — TNS

Hypothyroidism is a condition where the thyroid gland produces too little thyroid hormone (i.e. an underactive thyroid).

Congenital simply means that the condition exists at birth.

Congenital hypothyroidism is the most common preventable cause of mental disability in children.

Worldwide, it occurs in one in every 2,000 to 4,000 babies born.

In Malaysia, it is reported to occur in one in every 1,170 to 2,754 babies.

Babies with congenital hypothyroidism often look normal and healthy at birth.

Hence, screening for this condition is done at birth in many countries, including Malaysia, to ensure prompt detection.

With early treatment, babies with congenital hypothyroidism can grow and develop normally.

Babies who are not treated will gradually develop serious complications such as mental retardation and poor growth.

Essential for growth

The thyroid gland is a butterfly-shaped gland located in the front of the neck.

It produces the thyroid hormones thyroxine (T4) and triiodothyronine (T3).

Thyroid hormones are crucial for normal brain development in babies and children, especially during the first three years of life.

Thyroid hormones are also important for growth and regulating body metabolism to maintain normal temperature, heart rate, energy levels and bowel movement.

During early pregnancy, the baby’s thyroid gland begins to form at the back of the tongue and moves to its normal position in the neck by the eighth week of pregnancy.

In some babies, the gland does not develop properly or may not move to the normal position.

This is known as thyroid dysgenesis, and is the most common cause of congenital hypothyroidism.

This condition, which is not inherited and does not pose a risk to other siblings, include:

• A small, underdeveloped thyroid gland (thyroid hypoplasia).
• A thyroid gland that’s not located normally in the neck (ectopic thyroid gland).
• An absent thyroid gland (thyroid agenesis).

Other possible causes of congenital hypothyroidism are:

• Defective production of thyroid hormones (dyshormogenesis), which is usually an inherited condition.
• Problems with the pituitary gland (central hypothyroidism), which is less common and may be associated with other pituitary hormone or brain abnormalities.
• Mother’s thyroid disease, iodine deficiency or medicines taken during pregnancy, which is often transient.
• Babies with chromosomal disorders such as Down syndrome, Turner syndrome and William syndrome, are at higher risk and must have their thyroid function monitored regularly.

Screening at birth

In Malaysia, all babies delivered at hospitals are screened at birth by blood taken from their umbilical cord.

The screening test measures a hormone called thyroid-stimulating hormone (TSH).

TSH is produced by the pituitary gland in the brain and is a messenger to tell the thyroid gland to make more thyroid hormones.

Hence, if thyroid hormones are low, the brain makes more TSH to tell the thyroid gland to “work harder”.

If the TSH test is abnormal, the baby will need to have a small amount of blood taken from one of their veins to confirm the diagnosis.

Babies with the following conditions would need another screening test two to four weeks after birth, even if their initial test is normal:

• Born premature or small for their gestation age (i.e. a birth weight of less than 2.5kg).
• Very ill at birth.
• Prolonged jaundice (usually occurring after two weeks of life).
• Risk factors for developing congenital hypothyroidism, e.g. chromosomal disorders.

As mentioned above, most babies with congenital hypothyroidism appear normal and healthy at birth and during the first few months of life.

Some babies may develop these signs and symptoms:

• Persistent jaundice (yellowing of the skin and eyes) after two weeks of life
• Constipation
• Poor muscle tone
• Sluggishness and/or sleeping excessively
• Hoarse cry
• Poor sucking and feeding problems
• Thick, large tongue
• Puffy-looking face
• Goitre (swelling at the neck due to enlargement of the thyroid gland)
• A full abdomen with outpouching of the belly button
• Wide fontanelles (the soft spots between the skull bones)
• Poor growth.

Effective treatment

If congenital hypothyroidism is not treated, complications can include mental disabilities, poor growth and adverse effects on the heart.

Early diagnosis and proper treatment can prevent these problems.

Treatment aims to restore thyroid hormone levels to normal with a synthetic form of thyroid hormone called levothyroxine.

Although levothyroxine is synthetic, it is identical to the thyroid hormone T4 produced by the body.

It is available in tablet form, so parents can crush the tablet and mix it with a small volume, i.e. a few millilitres, of expressed breast or formula milk.

This can then be given to the baby on a teaspoon or in a syringe.

The tablet should not be mixed in a whole bottle of milk.

It should also not be given with soymilk or supplements that can interfere in its absorption by the body.

It is very important that parents administer levothyroxine daily according to the prescribed dose.

Prepared suspension forms of levothyroxine are not stable and should not be used.

It is very important for the baby to undergo regular monitoring of blood thyroid hormone levels (TSH and free T4) to ensure that they are receiving the correct amount of medication to maintain their thyroid hormones at the recommended levels.

In general, it is recommended that babies with congenital hypothyroidism be managed in consultation with a paediatric endocrinologist or a paediatrician with experience in treating this condition.

In most cases, congenital hypothyroidism is a permanent condition and thyroid hormone replacement therapy will be needed for the rest of the child’s life.

In some cases, the treatment time is temporary, lasting a few months to few years.

If there is a possibility that the condition is temporary, reassessment on whether a child needs to continue treatment is usually done after they are three years old, by which time critical brain development is completed.

In some mild cases where transient causes are suspected, treatment is sometimes stopped earlier with continued close monitoring of blood tests.

The medication must never be stopped without prior consultation with a paediatrician or paediatric endocrinologist.

In the past, before screening for congenital hypothyroidism was developed, untreated babies who were not diagnosed developed mental disabilities and severe short stature in childhood.

Currently, with early detection and replacement of thyroid hormones, the long-term outcome is excellent.

Children with congenital hypothyroidism on appropriate replacement of their thyroid hormones are able to develop and grow normally, and lead happy, regular lives.

Dr Jeanne Wong Sze Lyn is a consultant paediatrician and paediatric endocrinologist. This is the eighth article in a monthly series called Hormones and Kids. For more information, email [e-mail]. The information provided is for educational purposes only and should not be considered as medical advice. The Star does not give any warranty on accuracy, completeness, functionality, usefulness or other assurances as to the content appearing in this column. The Star disclaims all responsibility for any losses, damage to property or personal injury suffered directly or indirectly from reliance on such information.