In the case of a mother who is Rh negative and has an Rh positive fetus, what medication is administered to prevent complications?

When a mother is Rh negative and carries an Rh positive fetus, there is a risk of Rh incompatibility, which can lead to hemolytic disease of the newborn (HDN). This condition occurs when the mother's immune system produces antibodies against the fetal Rh positive blood cells, leading to potential complications for the fetus, including anemia, jaundice, and more severe outcomes like heart failure or fetal death.

To prevent these complications, Rho(D) immune globulin is administered to the mother, typically during the third trimester and within 72 hours after delivery if the infant is found to be Rh positive. This medication works by preventing the mother's immune system from recognizing and attacking the Rh positive blood cells. It effectively neutralizes any Rh positive cells that might have entered the maternal circulation, thus preventing the development of antibodies that could harm the fetus.

The other options do not address the issue of Rh incompatibility. Vitamin K is used to prevent bleeding in newborns but has no effect on Rh issues. Antibiotics target infections and do not relate to Rh incompatibility. Blood transfusions would be a treatment for a baby already affected by severe anemia but are not a preventive measure for the mother during pregnancy.