**Core Concept:** Isoimmunisation occurs when the maternal immune system produces anti-D antibodies in response to Rh-positive fetal blood entering the maternal circulation, leading to hemolytic disease of the newborn. Predisposing factors include Rh incompatibility between the mother and fetus, lack of Rh immunoglobulin G (RhIgG) prophylaxis, and multiple pregnancies. Rh-ve stands for Rh-negative blood type.

**Why the Correct Answer is Right:** The correct answer is not provided in the question, but it is crucial to understand the factors that do not predispose a Rh-ve female to isoimmunisation. In this case, the focus is on the factors that protect the Rh-ve female from developing isoimmunisation.

**Why Each Wrong Option is Incorrect:**

A. **Option A:** Being pregnant with an Rh-positive fetus does not predispose an Rh-ve female to isoimmunisation. In this scenario, the fetus is Rh-positive, which means its blood type is different from the mother's. This difference triggers the immune response, leading to isoimmunisation.

B. **Option B:** Multiple pregnancies do not protect an Rh-ve female from isoimmunisation. In fact, multiple pregnancies increase the risk of isoimmunisation due to repeated exposure to Rh-positive blood.

C. **Option C:** Lack of RhIgG prophylaxis does _not_ protect an Rh-ve female from isoimmunisation. RhIgG prophylaxis involves administering RhIgG to Rh-ve females during the first trimester to prevent isoimmunisation. If this prophylaxis is absent, it increases the risk.

D. **Option D:** Having a Rh-positive fetus does not protect an Rh-ve female from isoimmunisation. Similar to option A, the fetus's Rh-positive blood type triggers the immune response in an Rh-ve mother.

**Clinical Pearl:** To prevent isoimmunisation, Rh-ve females should receive RhIgG prophylaxis during the first trimester and again after the 28th week of pregnancy. Additionally, Rh-ve females should receive a blood transfusion with Rh-negative blood if Rh-positive blood is necessary. This prophylactic approach significantly reduces the risk of isoimmunisation and its complications in newborns.