52: Serum concentrations of TSH, T4 and T3 in fullterm, preterm and small-for-gestational age newborns

Abstract

A total number of 103 fullterm (FT), 47 small-for-gestational age (SGA) and 35 preterm (PT) babies were studied from day 1–8 after birth. In FT a surge of TSH was invariably seen, followed by a decrease until normal adult levels were reached on day 2–4 after birth. Serum T4 and -T3, concentrations were higher than in adults, significantly correlated and decreased by 30 and 40% respectively from day 2 to 8 after delivery. In SGA the postnatal TSH hypersecretion was more variable. Serum T4 and -T3, concentrations were significantly correlated and lower than in FT. Serum T4 decreased insignificantly and serum T3 seemed to increase during the first week of life. In PT the postnatal TSH increase was highly variably. Serum T4 and -T3 were lower than in FT and did not change significantly during tne study period; serum T3 tended to increase. Birth weight as well as gestational age were correlated with the thyroid hormone concentrations. In babies with gestational age of more than 34–36 weeks normal serum T4 and T3 concentrations were often observed.It is concluded that the postnatal pituitary-thyroid hyperfunction may be subnormal in SGA and PT babies. If serum TSH concentration is not measured in screening for congenital hypothyroidism these babies may appear as false positives.