Plasma β-Endorphin in Neonates: Effect of Prematurity, Gender, and Respiratory Status

A consecutive cohort of 87 infants (46 infants <37 weeks gestational age and 41 term infants ≤37 weeks gestation) admitted to the Neonatal Intensive Care Unit (NICU) and a convenience cohort of 27 term well babies at the University of Nebraska Medical Center (Omaha, NE) were evaluated for plasma β-endorphin (βE) levels during the first 4 h after birth. Demographic data, maternal history, and respiratory status at the time of sampling as well as development of documented apneic episodes during the initial hospitalization were analyzed for all infants. All NICU infants had higher plasma βE levels than the control infants. Premature infants had significantly higher neonatal plasma βE levels than term infants in either the control or NICU groups, but the response was gender specific; premature males had higher plasma βE than premature females (P = 0.008). Perinatal stress, including respiratory problems, was associated with the increase in plasma βE, but prematurity and being male were significantly predictors of an elevated plasma βE level. Immaturity in respiratory control, as evaluated by the development of documented apneic episodes during the infant’s initial hospitalization, did not correlate with an elevated perinatal plasma βE level.