All predisposes to isoimmunisation in a Rh-ve female except :
**Core Concept**
Isoimmunization in a Rh-negative female occurs when her immune system reacts to Rh-positive blood from her fetus or during blood transfusion, leading to the production of antibodies against Rh-positive blood. This can cause hemolytic disease of the newborn (HDN) in future pregnancies with Rh-positive fetuses.
**Why the Correct Answer is Right**
The primary risk factor for isoimmunization is exposure to Rh-positive blood, which can occur during pregnancy, childbirth, or blood transfusions. The Rh-negative mother's immune system recognizes the Rh-positive blood as foreign and mounts an immune response, producing antibodies against the Rh-positive blood cells. This can lead to the destruction of Rh-positive red blood cells in the fetus, resulting in hemolytic disease of the newborn.
**Why Each Wrong Option is Incorrect**
**Option A:** Pregnancy with an Rh-positive fetus is a well-known risk factor for isoimmunization, as the mother's immune system can react to the Rh-positive blood cells. This is the most common cause of isoimmunization in Rh-negative females.
**Option B:** Blood transfusions from Rh-positive donors can also expose an Rh-negative female to Rh-positive blood, leading to isoimmunization. This is another significant risk factor for developing antibodies against Rh-positive blood.
**Option C:** Fetal-maternal hemorrhage (FMH) during pregnancy or childbirth can also lead to isoimmunization in Rh-negative females. This occurs when Rh-positive fetal blood enters the maternal circulation, triggering an immune response.
**Clinical Pearl / High-Yield Fact**
Rh immunoglobulin (RhIg) is a crucial drug used to prevent isoimmunization in Rh-negative females who have received Rh-positive blood transfusions or have had a fetal-maternal hemorrhage. It works by binding to and inactivating the Rh-positive blood cells, preventing the immune response.
**Correct Answer:** D.