Thyroid function in healthy and sick neonates

Low serum thyroid hormone concentrations are frequently observed in critically ill patients. Low-birth-weight preterm infants have also been reported to contain lower serum thyroxine (T4) levels when compared with normal term infants. Investigating the differences of the thyroid function between sick and healthy term and preterm infants becomes a worthwhile task.

Thyroid functions were measured in 80 newborn infants (including 31 critically ill neonates admitted to neonatal intensive care unit and 49 healthy controlled neonates). The neonates were divided into three groups in terms of gestational age. Group 1 consisted of 10 sick and 12 healthy term neonates with a gestational age > or = 38 weeks. Group 2 consisted of 9 sick and 26 healthy preterm infants with gestational ages ranging between 32 and 36 weeks. Group 3 consisted of 12 sick and 11 healthy very low birth weight (VLBW) infants with a gestational age < or = 31 weeks. Serum thyroxine (T4), thyroid stimulating hormone (TSH), free T4, and triiodothyronine (T3) concentrations were measured at 1 and 5 days after birth.

Observed data indicated that sick neonates in three groups had significantly lower T4 values (p = 0.05) than healthy term and preterm neonates. TSH levels of sick neonates in three groups were not significantly different (p > 0.05) from those of healthy neonates on day 1 and day 5. Serum free T4 levels were significantly lower (p < 0.05) in sick than in healthy premature infants. Sick VLBW premature infants had significantly lower T3 values (p < 0.05) than healthy VLBW premature infants on day 1 and day 5.

Low serum T4, free T4, T3 concentrations are commonly found in sick neonates, whereas serum TSH values are not significantly different between sick and healthy neonates.