Which of these situations could cause hemolytic disease of the newborn?

Hemolytic disease of the newborn (HDN) primarily occurs when there is an incompatibility between the blood types of the mother and the fetus, specifically involving the Rh factor or ABO blood groups.

In the case of an O- mother and an O+ fetus, the mother’s O- blood type means she does not have the Rh antigen. If she carries an O+ fetus, the fetus has the Rh antigen, which can lead to the mother producing antibodies against the Rh factor if fetal red blood cells cross into her circulation. This immunological response can then affect the fetus by causing hemolysis of the red blood cells, leading to HDN.

Other scenarios such as an A+ mother with an A- fetus or a B+ mother with a B+ fetus are less likely to cause HDN since there is no Rh incompatibility present. Similarly, an AB+ mother with an AB- fetus, while it might introduce some measures of incompatibility, does not significantly predispose to hemolytic disease in the same way as a combination of O- and O+ does, particularly due to the absence of the Rh factor in the mother. Thus, the O- mother carrying an O+ fetus is the situation that most clearly presents