Transitory “euthyroid sick syndrome” in pre-term infants of fetal age ≤ 31 weeks

Abstract

Serum T4,FT4, T3, rT3, TSH,Tg, and TBG were measured by RIA in 37 pre-term infants of postmenstrual age ≤ 31 weeks.Blood was withdrawn at day 0 and 10,20,30 and 40 days after birth.From day 10 on, 17 infants were treated with either T3 (5 μg/kg.day) or T4 (10 μg/kg.day) because of failure to thrive. The 25th,50th and 75th centile values were calculated and compared with those obtained in 20 well thriving infants. In the control group,T3 (ng/dl) at birth is low (45-81-108) increasing to (119-155-187) while rT3 (ng/dl) falls from (170-192-225) to (60-98-123).The 50th centiles of T4,FT4 and TBG remain rather stable throughout the study around birth levels at 4-5 μg I/dl,1.5 ng/dl and 2 mg/dl respectively.Patients have significantly lower levels of T4,FT4, T3 and TBG at birth and at day 10;Tg is significantly lower at birth; T3 at day 10. T3 treatment results in increased levels of T3 and TBG and lowered T4,FT4 and rT3.T4 treatment is associated with low TBG and T3 levels despite normal levels of T4, FT4 and rT3. No significant differences in TSH levels are found. These data suggest that in some pre-term infants an “euthyroid sick syndrome” might exist for some time after birth; thyroid hormone therapy might counteract failure to thrive.