Thymus Size and its Relationship to the Respiratory Distress Syndrome and Cord Blood Cortisol Level in the Preterm Infants

ABSTRACT

PURPOSE: Thymic size can be affected by glucocorticoids which promotes surfactant synthesis in preterm infants. We assessed the hypothesis that the fetal lung maturity in preterm infant correlates with the size of the thymus detected at birth on the routine chest radiograph. We also searched for a possible relationships between thymus size, respiratory distress syndrome (RDS), and the cord blood cortisol level. METHODS: The cardiothymic/thoracic ratios (CT/T) within 6 hours after birth and cord blood cortisol levels were measured in 42 preterm infants admitted to the neonatal intensive care unit of Seoul National University Children's Hospital from June 2002 to December 2003. Multiple linear regression analyses were done to assess the relationships between the CT/T, the perinatal events and the cord blood cortisol levels. The receiver operation characteristic curve analysis was done to evaluate the CT/T in the prediction of RDS. RESULTS: 8 infants (19.0%) developed RDS. The CT/T positively correlated with the birth weight, but not with the gestational age. The CT/T were significantly larger and the cord blood cortisol levels were significantly lower in the preterm infants with RDS than in those without RDS. The cord blood cortisol levels were negatively correlated with the CT/T. The birth weight and RDS were all independently associated with the CT/T. The CT/T less than 0.37 identified infants with RDS with 87.5% sensitivity and 61.8% specificity. CONCLUSION: The larger thymus at birth can be used to identify RDS. The lower cord blood cortisol level may be associated with the larger thymus in RDS.