**Core Concept:**
The question is related to the risk of transmission of Anti-D Immune Globulin (BiH) to a neonate from a reactive mother with Anti-D antibodies. BiH is a preparation of Anti-D antibodies used to prevent RhD haemolytic disease in infants born to RhD negative mothers with RhD positive babies. The risk of transmission can be assessed using various parameters.

**Why the Correct Answer is Right:**
The correct answer is C: **"The age of the mother"**. The risk of transmission of Anti-D antibodies from a reactive mother to the infant is determined by factors such as the presence of Anti-D antibodies in the mother's blood, the timing of administration of BiH, and the gestational age of the infant at birth. The age of the mother is not directly related to the risk of transmission.

**Why Each Wrong Option is Incorrect:**
A: **"The mode of delivery"** - The mode of delivery (vaginal vs cesarean section) does not affect the risk of Anti-D antibodies transmission to the infant. The risk is primarily determined by the presence of Anti-D antibodies and gestational age.

B: **"The gender of the infant"** - The gender of the infant is unrelated to the risk of Anti-D antibodies transmission. The risk is determined by the mother's antibodies and the infant's RhD status, not the infant's gender.

D: **"The mother's blood group"** - The mother's blood group is not relevant to the risk of Anti-D antibodies transmission to the infant. The risk is determined by the mother's Anti-D antibodies and the infant's RhD status, not the mother's blood group.

**Clinical Pearl:**
When assessing the risk of RhD haemolytic disease in an infant due to Anti-D antibodies from a reactive mother, consider the following factors:
1. The presence of Anti-D antibodies in the mother's blood.
2. The gestational age of the infant at birth.
3. The infant's RhD status (positive or negative).

By focusing on these three key factors, you can accurately assess the risk of transmission of Anti-D antibodies to the infant and determine the appropriate timing and mode of administration of Anti-D immunoglobulin (BiH) to prevent RhD haemolytic disease in the infant.