Using the Ballard Gestational Age Assessment Tool, the nurse determines that a 15-minute old client has a gestational age of 42 weeks. Based on this finding, which intervention is most important for the nurse to implement?

A: Apply a pulse oximeter to the foot. Continuous monitoring of oxygen saturation can help detect hypoxemia early, which can be a concern in post-term infants due to potential respiratory distress or meconium aspiration. However, while important, this is a monitoring measure and not an immediate corrective action for potential metabolic or respiratory issues directly associated with post-term birth.

B: Draw arterial blood gases. Arterial blood gases (ABGs) provide critical information about the newborn's acid-base balance, oxygenation, and ventilation status. Post-term infants are at risk for hypoxia and acidosis, often due to placental insufficiency or meconium aspiration. However, obtaining ABGs can be invasive and might not be the first-line immediate action unless there are signs of severe distress.

C: Obtain a capillary blood glucose. Post-term infants are at increased risk for hypoglycaemia due to increased glucose utilization and possible depletion of glycogen stores. Hypoglycaemia can lead to serious complications if not promptly identified and managed. Therefore, checking blood glucose levels is a critical, non-invasive, and immediate step to ensure metabolic stability and prevent complications such as seizures and brain injury.

D: Provide blow-by oxygen. Blow-by oxygen is used to provide supplemental oxygen in a non-invasive manner and can help in cases of mild respiratory distress. Post-term infants can be at risk for respiratory issues, including meconium aspiration syndrome. However, this is usually applied when there is evidence of respiratory distress and not as a routine measure without specific indications.