Does Hypothyroxinemia of Preterm Neonates Persist Beyond 7 weeks of Life?

OBJECTIVES

To determine whether hypothyroxinemia in the early neonatal period normalizes by 7 wk of postnatal age.

METHODS

An observational study was carried out from July 2008 through June 2010 in the neonatal and postnatal unit of Chittagong Medical College Hospital, Bangladesh. A total of 150 neonates including 100 preterm and 50 term neonates were selected by convenient sampling. Preterm neonates were stratified according to postconceptional age. By the 3rd generation two site chemiluminesent immunometric assay, free T4 (FT) and thyroid stimulating hormone (TSH) estimations were done. Within 5-11 d, first samples were collected from all the neonates and the second samples of hypothroxinemic preterm neonates were collected within 42-50 d of birth.

RESULTS

Positive correlation of FT was found with gestational age (p < 0.0001, n = 100, r = 0.61) in preterm neonates while significant difference was found among the gestational age subgroups (p = 0.0001). No significant differences were, however, found in TSH levels of such age groups of the preterms. Highly significant differences in FT and TSH levels between 1st and 2nd samples were found in subgroup analysis of the preterm neonates. In the 1st samples, TSH level correlated positively with gestational age but in the 2nd samples, significant negative correlation was observed. In all neonates with initial hypothyroxinemia, FT levels were found to increase to reach the normal levels by 7 wk.

CONCLUSIONS

FT level normalizes by 7 wk of birth in preterm newborn neonates.