Just so happens my daily pregnancy blog was on just that. Rhesus negative etc. Copy and paste below. Hope it helps:
During pregnancy, you will have a number of blood tests to screen for a variety of conditions. At your very first appointment, your blood will be taken to determine your blood group. There are four possible blood types: A, B, AB and O.
Each blood type then has a subcategory: positive or negative (for example, your blood type may be O negative). This second category refers to your rhesus factor. If your blood is rhesus positive, you have a protein known as D antigen on the surface of your red blood cells. If you don’t have this D antigen, you are rhesus negative.
Rhesus negative and pregnancy
15 percent of women are rhesus negative. It isn’t usually a cause for concern during a first pregnancy, but extra care may be needed to prevent problems arising during a later pregnancy.
A rhesus negative mother can carry a rhesus positive baby. Babies have their own blood supplies, but it is normal in pregnancy for a small amount of the baby’s blood to leak into the mother’s blood supply. Bear with me because it’s about to get a bit scientific. In this instance, there is an 80 percent chance that the mother’s rhesus negative blood will produce anti-D (the antibody to the D antigen carried in rhesus positive blood) to destroy the D antigen present in the baby’s rhesus positive blood. This transfer could also potentially occur during birth or injury.
Will it harm my baby?
In a first pregnancy, the production of anti-D isn’t too troubling, but the anti-D will stay in the mother’s body. If the mother later becomes pregnant with another rhesus positive baby, the anti-D may pass through the placenta and attack the baby’s red blood cells. This could cause haemolytic disease which leads to jaundice and anaemia in newborn babies. Luckily, the chances of this happening today are very small thanks to science and medicine.
Treatment
You will be tested early in the pregnancy to determine your blood type. If you are found to be rhesus negative, you will be offered an anti-D injection. This injection reduces your chance of producing anti-Ds, and destroys any anti-Ds already in your bloodstream. The injection is usually administered around the 28th week of pregnancy. Each pregnancy will require a new anti-D injection.
After the birth
A cord blood sample will be taken after the birth to determine the baby’s blood type. If the baby is rhesus positive, you will be offered a second injection to destroy any anti-D cells produced during the delivery.