Final answer:
When assessing a formula-fed newborn, a nurse primarily evaluates the infant's formula intake and digestion due to immature neonatal kidneys and their need for adequate hydration.
Step-by-step explanation:
When assessing a newborn who is formula-fed, a nurse would prioritize evaluating the formula intake and digestion of the newborn (Option D). This assessment is essential, given that the neonatal kidneys are still maturing and have a limited ability to concentrate urine. Newborns need to consume adequate fluids to avoid dehydration, making it important to ensure they are effectively digesting formula.
Aspects such as the mother's breast milk production would not be relevant in this context as the infant is formula-fed. Attention to the newborn's umbilical cord care remains important in overall neonatal care, but is not directly related to feeding concerns. The mother's dietary preferences are also not a primary concern when assessing formula-fed newborn nutrition.