Neonatal hypothyroxinemia: Effects of iodine intake and premature birth

We have investigated the effects of iodine (I) intake on urinary I excretion in preterm (PT) babies up to 2 months after birth and its effect on serum T-4, free T-4 (FT4), T-3, TSH, and thyroglobulin (Tg) levels compared to those in term (T) newborns. Very premature and very sick infants were in negative I balance for the first weeks after birth. Later, these same infants, as well as the other PT and T newborns, were in positive balance; 75-80% of the ingested I was not accounted for in the urine. The urinary I levels of PT and T neonates cannot be equated to their I intakes. T-4, FT4, and T-3 levels in PT and T neonates increased with postmenstrual age, whereas Tg decreased and TSH did not change. Serum FT4, T-3, Tg, and TSH levels in PT neonates were affected negatively, independently from age, by a low I intake. PT birth also affected T-4, FT4, and Tg negatively, independently from I intake and postmenstrual age, for at least 6-8 weeks after birth. Care should be taken to avoid I deficiency in PT neonates. However, even when I intake is adequate, PT newborns are hypothyroxinemic compared to T babies during an important period of brain development. This suggests the possible convenience of interventions that might mimic the intrauterine hormone environment and accelerate maturation.