Thyroid Function in Term Infants With Respiratory Distress

Transient hypothyroxinemia, as demonstrated by low T4 and free T4 levels with normal levels of TSH, in preterm infants has been associated with increased severity of illness and adverse outcomes. Effects of thyroid function in term infants is less well studied. Previous research in the Special Care Nursery at Christiana Hospital has indicated that transient hypothyroxinemia in intubated term infants was associated with increased severity of illness and the need for more intensive rescue therapies. However, free T4, the biologically active substance was not measured in our previous study. Infants who meet criteria for the study will begin participation after parental informed consent is obtained. Infants who are enrolled will have serial measurements of thyroid stimulating hormone (TSH), T4, free T4, free T3, and cortisol. These measurements will be obtained at four specific time intervals throughout the first week of the infant's life. The medical team will be blinded to the results of the hormone testing. The results will be reviewed by an unblinded study investigator and an endocrinologist will be consulted if abnormal results are reported. These hormone levels will be compared with severity of illness and level of respiratory support needed in order to establish an association between thyroid function and illness severity. Illness severity will be quantified by using the Score for Neonatal Acute Physiology (SNAP). SNAP scores require collecting data from vital signs and results of labs that are considered standard of care.