ESPE Abstracts

Background: In premature neonates hypothyroidism or thyroid sick syndrome is frequently diagnosed, which is a result of the immaturity of the gland itself and the hypothalamic–pituitary–thyroid axis. The necessity of rapid adaptation to extrauterine life, generation of high thermal energy, and accelerated development of the central nervous system is the cause of the increased demand for thyroid hormone.

Objective and hypotheses: The aim of our study is to determine the benefits of early levothyroxine (L-T₄) substitution therapy in premature neonates and to determine the optimal dose of the drug. The prospective, longitudinal studies were conducted during 7 years in 134 premature neonates with low and very low body weight by delivery.

Method: The 82 children with a reduced fT₄ level received L-T₄ therapy at the doses of 5–7 μg/kg BW/day, since the 2nd week of life. The control group comprised 52 children with normal TSH, in whom the level of thyroid hormones were determined 4 weeks and later after birth; afterwards, they received L-T₄ therapy. The physical and mental development were compared. The mental development and IQ was assessed in the Wechsler Intelligence Scale for Children in the 7th year of life.

Results: The preterm born neonates were observed to have a more rapid body weight gain in the first period of life after administration of L-T₄. In this group, all infants acquired the motor functions statistically significantly earlier in comparison to the infants from group with delayed treatment. In the 7th year of life, the IQs were significantly higher (103.6±20.1) in group 1 treated since the 2nd week of life in comparison to group 2 (83.3±21.3).

Conclusion: The early replacement therapy with L-T₄ in doses 5–7 μg/kg BW/day initiated in the 2nd week of life may improve physical development in the newborn period and long-term mental development in preterm-born children.