One of the blood tests we take at your booking appointment is to check your blood group.
Your blood group is inherited from your parents and, in turn, your baby will inherit his or her blood group from either you or their father.
Most women are rhesus ‘positive’, but if you are among the one in 10 women who are rhesus ‘negative’ the plan for your pregnancy will be slightly different.
Although your blood does not normally come into contact with that of your baby during pregnancy, there are times when this can happen – particularly following an episode of bleeding, and at birth when the placenta or ‘afterbirth’ separates.
If you are blood group rhesus positive, a small amount of mixing between your blood and that of your baby will cause no problems to either of you.
If you are rhesus negative, the mixing of the baby’s blood with your own during pregnancy or at delivery can cause you to produce antibodies that will remain in your blood permanently.
These antibodies will not affect you in anyway but can cross the placenta to affect your unborn baby. Because of this risk, all women who are rhesus negative are offered an injection of a substance called ‘anti D’ to help to prevent the formation of antibodies during the pregnancy and after the birth of the baby.
What is anti D?
Anti D is a product derived from donated human blood. It is extracted from the blood and given as a single injection into your arm when you are 28 weeks pregnant.
The anti D forms a coating over any of the baby’s blood cells that may mix with yours and prevents your body from recognising them, so that it will not produce antibodies harmful to your unborn baby.
After your baby is born, some of your baby’s blood will always pass into yours. If you are rhesus negative, this can result in antibodies being formed even after the birth.
Although these cannot affect the baby you have just given birth to, the antibodies would remain permanently in your blood and may affect any future babies you have.
For this reason we would routinely offer you a further dose of anti D after birth.
However, you will only need this if your baby is found to be rhesus positive. If your baby is rhesus negative like you, you will not require this dose.
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