Thyroid function in the preterm infant

Area of Science:

• Neonatology
• Endocrinology
• Developmental Biology

Background:

• Thyroid gland function is crucial for fetal development, with thyroxine (T4) production starting around 12 weeks gestation.
• Preterm infants exhibit lower cord serum T4 and free T4 (FT4) concentrations, correlating with gestational age and birth weight.
• Postnatal thyroid hormone levels in preterm infants show a blunted surge compared to term infants, with potential declines in the first week.

Purpose of the Study:

• To review the development and changes in thyroid hormone levels in preterm infants.
• To explore factors contributing to thyroid hormone fluctuations in prematurity.
• To evaluate the efficacy of thyroxine (T4) supplementation for medical and neurological outcomes in preterm infants.

Main Methods:

• Analysis of existing studies on thyroid hormone concentrations in preterm infants.
• Review of factors influencing thyroid hormone levels, including prematurity complications like respiratory distress syndrome (RDS).
• Evaluation of clinical trial data on T4 treatment for preterm infants' medical and neurological outcomes.

Main Results:

• Preterm infants often experience a fall in serum T4 and T3 postnatally, influenced by nutritional issues, immaturity, and increased T4 utilization.
• Serum FT4 levels appear less affected by prematurity and illness compared to total T4.
• While T4 treatment shows limited benefits for medical complications, one study indicated improved IQ in infants <27 weeks gestational age.

Conclusions:

• Thyroid hormone dynamics in preterm infants are complex, affected by immaturity and illness.
• Current evidence does not strongly support T4 supplementation for general medical complications in preterm infants.
• Further research is needed to ascertain potential neurological benefits of transient T4 supplementation in extremely preterm infants (<27 weeks gestation).