Science Questions

Can blood types cause problems with pregnancy?

Sun, 2nd Sep 2007

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Question

Colin asked:

My girlfriend has O negative blood and I have O positive. I've heard that this can cause problems with pregnancy, is this true? If so, what are the consequences?

Answer

This is called the rhesus effect.  The rhesus gene adds an extra 'label' to the surface of your red blood cells, like the labels for group A or group B, this is type D.  If you are rhesus negative as a mother, it means you will not have any antibodies to this label in your blood, as your immune system has never seen it.  If your partner is rhesus positive there is a chance that a baby you conceive will be rhesus positive too.
When the baby is born, blood from the baby can get into the mother's blood stream, and so the mother makes antibodies against the baby's blood.  This wont harm the baby this time round, but may cause complications during the next pregancy.
Mothers protect their baby from 30 weeks by putting a cross section of their antibodies into the baby's circulation.  This will now include the "anti-D" antibodies, so if the baby is rhesus positive these antibodies will lock onto their blood cells and start to destroy them.  This can mean the baby becomes anaemic inside the womb, and so you either need to induce birth quickly or give the baby a blood transfusion inside the uterus.  To prevent this happening in the first place, rhesus negative women are given a dose of Anti-D antibodies, up to 72 hours after her first baby if they couldn't determine the baby's blood type.  The anti-D antibodies soak up any of the baby's blood so that the mother's immune system doesn't know how to make these antibodies.

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