The introduced antibodies will destroy any foetal cells that enter the mother's blood before her system has a chance to send a signal to create natural antibodies.

Normally, one shot of RhoGam is given at 28 weeks of pregnancy and another after the birth (or miscarriage, termination or amniocentesis).  This is because the greatest chance that the baby's blood can enter the mother's system is between 28 week and delivery.  The same process is repeated for each pregnancy.

Normally, an Rh negative mother with an Rh positive baby has roughly a 15% chance of forming lifelong natural antibodies unless the injections are used.  When used correctly, this treatment reduces the risk to about 0.07%.

Remember: The mother and current baby are not normally at risk, it is future pregnancies that are at risk if natural antibodies are formed.

This is a relatively new treatment and was only discovered in the last few decades.  My own mother is Rh negative and had five healthy Rh positive pregnancies before the injections were available but this was not the norm and many Rh negative women lost babies because of this disease.

1. What is Rh Disease and what causes it?

2. How can Rh Disease be prevented?

3. What are the treatments for Rh Disease?