What results from an immature renal system in preterm infants?

The correct answer is that an immature renal system in preterm infants leads to an increased likelihood of fluid retention. This is due to the kidneys of preterm infants being underdeveloped, which affects their ability to excrete waste products and regulate fluid balance effectively. As such, these infants are less capable of handling fluid loads, making them more prone to conditions such as edema and supporting the risk of fluid overload.

In contrast, the other options suggest capabilities that preterm infants do not possess due to their immature renal function. Preterm infants generally have decreased ability to concentrate urine, which would negatively impact their fluid management, not improve it. Similarly, the renal system's lack of maturity means it does not have an increased ability to retain electrolytes or demonstrate improved selectiveness in filtration—these functions would typically be compromised in such underdeveloped kidneys. Thus, the immaturity of the renal system fundamentally increases the risk of fluid retention, emphasizing the need for careful fluid management in this vulnerable population.