The lungs of the fetus are filled with fluid and it is essential that fetal lung fluid is cleared at birth. This process is mediated through the activation of airway epithelial sodium channels (ENaC). In animals, ENaC is considered crucial for postnatal pulmonary adaptation. In humans, postnatal ENaC expression is dependent on gestational age and its activity, measured as nasal potential difference, correlates with lung compliance. Therefore, in the human newborn infant ENaC may be important for physiologic postnatal adaptation. The activity of ENaC is increased by beta-agonists, such as salbutamol. We hypothesize that low pulmonary expression or activity of ENaC in the perinatal period causes delayed clearance of lung fluid and thereby contributes to the risk for development of transient tachypnea of the newborn (TTN) in term infants born by Caesarean section (CS).