How is thyroid function in preterm infants?

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Thyroid function in preterm infants

Thyroid dysfunction is common in preterm infants. Congenital hypothyroidism causes neurodevelopmental impairment, which is preventable if properly treated. According to studies, hypothyroidism is more common in preterm infants than in term infants. Preterm infants have lower levels of tri-iodothyronine (T3) and free thyroxine (T4) than term infants during the first several weeks.

Causes of hypothyroidism in preterm infants

Several factors are known to contribute to hypothyroidism in preterm infants, including:

An immaturity of the hypothalamic-pituitary-thyroid axis,
An immaturity of thyroidal capacity to concentrate and synthesize iodine,
An immaturity of thyroid hormonal metabolism,
Iodine insufficiency and iodine excess

Characteristics of hypothyroidism in preterm infants

Thyroid gland function develops and matures during fetal life, with production of serum thyroxine (T4) concentrations beginning around 12 weeks gestation and increasing to term. Infants born prior to term have lower cord serum T4 concentrations that correlate with gestational age or birth weight. This is partially the result of lower thyroxine-binding globulin (TBG) concentrations. In contrast to term infants, preterm infants often experience a fall in serum T4 and T3 in the first week of life to below birth levels.

Does this hypothyroidism matter?

Severe hypothyroxinaemia, as measured on blood spots in newborn screening programs has been associated with the followings:

An increase in perinatal mortality and morbidity
An increased risk of neurodevelopmental problems
Reduced intelligence quotient (IQ)
And disabling cerebral palsy

Treatment

Treatment for a newborn with thyroid disease is more successful when started within the child’s first month of life. If left untreated, low thyroid hormones can lead to problems with the nervous system or developmental delays. However, doctors regularly screen babies within the first four weeks of life, so these problems don’t usually occur.

Hyperthyroidism, an overactive thyroid gland, is seen only occasionally in newborns. If the mother has Graves’ disease, the thyroid-stimulating antibodies in her blood can cross the placenta and stimulate the unborn child’s thyroid gland, thus producing too much thyroid hormone. No treatment may be necessary as the mother’s antibodies will soon clear from the baby’s bloodstream, usually within 2 to 3 months.