**Core Concept**
Anti-D gamma globulin is administered to Rh-negative mothers after delivery to prevent the formation of anti-Rh antibodies against the Rh-positive blood of the baby. This is a crucial measure to prevent hemolytic disease of the newborn (HDN) in subsequent pregnancies.

**Why the Correct Answer is Right**
The standard dose of anti-D gamma globulin given after term delivery is 300 micrograms. This dose is administered to prevent the passage of fetal Rh-positive blood into the maternal circulation, which would lead to the sensitization of the mother's immune system against the Rh antigen. The anti-D gamma globulin binds to any fetal Rh-positive red blood cells that may have entered the maternal circulation during delivery, preventing the mother's immune system from recognizing them as foreign and mounting an immune response. This ensures that the mother remains Rh-negative and does not develop anti-Rh antibodies that could cause HDN in future pregnancies.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as there is no standard dose of anti-D gamma globulin given after term delivery for a Rh-negative mother and Rh-positive baby.
**Option B:** This option is incorrect as the dose of anti-D gamma globulin given after term delivery is not 150 micrograms.
**Option C:** This option is incorrect as the dose of anti-D gamma globulin given after term delivery is not 450 micrograms.

**Clinical Pearl / High-Yield Fact**
The dose of anti-D gamma globulin given after term delivery should be administered within 72 hours of delivery to be effective. If the mother has received a blood transfusion or has had a cesarean section, the dose should be given within 24 hours of delivery.

**Correct Answer:** C. 300 micrograms