When is RhIg (Rhogam) not effective?

RhIg, commonly known as Rhogam, is a medication used to prevent Rh immunization in Rh-negative individuals who are at risk of developing antibodies against Rh-positive blood. The effectiveness of RhIg hinges on its administration prior to sensitization occurring. When an Rh-negative individual is exposed to Rh-positive blood, particularly during events such as pregnancy, labor, or a blood transfusion, their immune system may develop antibodies against the Rh antigen. Once this sensitization occurs, Rhogam is no longer effective in preventing the formation of these antibodies.

This is why the correct answer highlights that RhIg is not effective once sensitization has occurred. In situations where sensitization has already taken place, the individual has become immunized and will continue to produce Rh antibodies, which can lead to complications in subsequent pregnancies or transfusions.

In contrast, RhIg is typically administered at specific times during pregnancy, such as at the first prenatal visit, if there is a risk of sensitization. Administering it during labor can also be effective, provided it is given before any Rh-positive blood exposure occurs. After 28 days postpartum, RhIg can still be beneficial if the individual has not yet become sensitized, although timely administration is imperative for optimal effectiveness.