This study was designed to evaluate the level of certain hormones (thyroid hormones and cortisol) in full term or close to full term infants who have respiratory distress severe enough to require respiratory support. The purpose of this study is to determine if there is a relationship between these hormone levels and how sick these infants are who require help with breathing following birth.

Hypothesis: Infants who are born full term or near full term and who have low hormone levels will have higher severity of illness.

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.

Inclusion Criteria:

• Infants born > or = to 35 weeks gestation
• Infants admitted to the neonatal intensive care unit at Christiana Hospital
• Respiratory distress requiring use of mechanical ventilation or nasal CPAP (continuous positive airway pressure)
• Parental informed consent

Exclusion Criteria:

• Infants born < 35 weeks gestation
• Infants with documented congenital abnormalities which directly impact the cardiorespiratory system

Full-term and near-term infants with respiratory distress during the first 24 hours of life.