What is NOT a reason for a positive DAT on cord blood cells of a newborn?

A positive direct antiglobulin test (DAT) in cord blood reflects the presence of antibodies bound to red blood cells (RBCs) in the neonate. In this case, the correct choice focuses on a scenario that does not result in a positive DAT.

Immune anti-K antibodies from a K-negative mother cannot sensibly react with K-negative cells of her newborn because these cells do not express the corresponding antigen to which the mother's immune response (anti-K) would be directed. Therefore, there would be no binding of antibodies to RBCs in the cord blood, leading to a negative result in the DAT.

In contrast, the other scenarios all involve the presence of maternal antibodies that can bind to fetal RBCs due to the presence of specific antigens. For instance, high concentrations of Wharton's jelly may interfere with the test but do not actually account for a true positive DAT since it does not involve immune interaction. Likewise, immune anti-A and anti-D antibodies correspond to antigens present on the fetal blood cells, leading to a positive DAT result.