There are four main blood groups that people can have, A, B, O and AB. You are also classified either positive + or negative-. This refers to the presence or absence of Rhesus factor in your blood.
The Rhesus factor is a protein on the surface of your red blood cells. If you are positive, say O+ that means you have the protein, if you are blood group A and don’t have the protein then you are A-. Depending on your ethnic heritage, generally 18% of Australians are Rhesus negative.
In pregnancy sometimes foetal blood can inadvertently enter the mother’s circulation. This may be during an amniocentesis, from vaginal bleeding or trauma (even mild) to the abdomen.
If you are a Rh-ve (negative) blood group and your partner is Rh-ve, there is no problem in pregnancy as your baby will be negative. If you are negative and your partner is positive or you don’t know your partners blood group then your baby could be either positive or negative.
Your body is extremely good at recognising what is not supposed to be there, like a germ in your blood, or a Rhesus positive foetal blood cell if any mixing of maternal and foetal blood occurs. This means your Rhesus negative immune system will make antibodies to the foreign object, usually a germ, but in pregnancy it may be to your babies blood cells. It is generally not an issue for the current pregnancy but it can be for subsequent pregnancies, there is a 70% (high chance) that your body will try to reject the foetus if he or she is found to Rhesus positive. The condition that occurs when Rhesus positive blood has entered the maternal blood stream and antibodies form is called haemolytic disease of the newborn.
What can we do to help? Injections of antiD immunoglobulin will coat or hide the foetal cells from the mothers immune system so antibodies cannot form. AntiD is given after any bought of vaginal bleeding, an amniocentesis, CVS (chorionic villus biopsy), trauma, or during labour. Rhesus negative mothers should have the injection of antiD within 72 hours of delivery or after any of the sensitising events occur. We also use antiD routinely at 28 and 32 weeks of pregnancy to help prevent the occurrence of haemolytic disease of the newborn.
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