ESPE Abstracts

Background: With the increasing survival rate of extremely premature infants, neonatal thyroid dysfunction is more frequently observed clinically. Despite the guidelines, the timing of screening for neonatal thyroid function remains controversial, especially for premature infants. At present, there is no unified standard for serum FT3, FT4 and TSH levels of newborns of different gestational ages and postnatal days.

Objective: To analyze the change trend of thyroid function in neonates of different gestational age and postnatal day, and provide basis for the selection of screening and treatment time of neonatal thyroid dysfunction.

Methods: From June 1, 2020 to June 1, 2021, 359 neonates were selected as subjects, 23 possible related factors were collected to analyze the influencing factors of neonatal thyroid dysfunction statistically. FT3, FT4 and TSH levels were divided into groups 7±3 days, 14±3 days, 21±3 days and 28±3 days according to the day of postpartum examination, and divided into groups 28-31⁺⁶ weeks, 32-33⁺⁶ weeks, 34-36⁺⁶ weeks, ≥37 weeks according to the gestational age. Then analyzed the differences of neonatal FT3, FT4 and TSH in different gestational ages and postnatal days, and established the 25th, 50th and 75th percentile values of FT3, FT4 and TSH for newborns of different gestational ages and postnatal days.

Results: Neonatal FT3 and FT4 levels were positively correlated with gestational age. The main influencing factor of neonatal TSH level was birth weight, and the lower the birth weight, the greater the incidence of TSH elevation. In addition, compared with normal thyroid function group, the frequency of increased TSH was higher at 7±3 and 14±3 days of postpartum, the frequency of decreased FT3 and decreased FT3 with increased TSH was higher at 14±3 and 21±3 days of opostpartum. However, in most cases, the levels of FT3, FT4 and TSH of different gestational ages tend to be normal gradually with the increase of postnatal day.

Conclusion: Neonatal thyroid dysfunction is more common in premature infants. It is recommended a second screening test at 1, 2, 3, 4 weeks after birth for premature infants, babies with low birth weight and critically ill newborns. It is more reasonable to formulate the reference range of FT3, FT4 and TSH based on gestational age and postnatal day.