There are times in all pregnancies where blood from the mother and the baby may mix, such as when a bleed from the placenta occurs after 12 weeks. If both mother and baby have the same rhesus status, ie. they are both RhD-positive or both RhD-negative, this causes no problem. However if an RhD-negative mother is carrying a RhD-positive baby (inherited from a RhD-positive dad), your immune system may react to the baby's blood as if it were a "foreign invader" and produce antibodies against it. Once these antibodies are made, they cannot be removed, and in subsequent RhD-positive pregnancies they may attack and destroy the baby's red blood cells, causing anaemia, jaundice, liver or heart failure. Blood transfusions to the baby before or after birth are needed in severe cases. These problems can be prevented by giving RhD-negative mothers an injection of anti-D immunoglobulin after any bleeding, and again after the birth of RhD-positive babies. This is known as anti-D prophylaxis. The National Institute for Clinical Excellence (NICE) is now recommending routine anti-D at 28 and 34 weeks to all RhD-negative mothers to prevent antibodies being produced following small silent bleeds which happens in about 1 and 1.5% of all pregnancies.
Anti-D is manufactured from the plasma of human blood, and as with all blood products, there is a tiny possibility of viruses being transmitted from donor to woman. This happened in Ireland in the 1970s, when a small number of women are thought to have contracted hepatitis C through anti-D. This is extremely unlikely to happen today to women in the UK. The manufacture of anti-D is strictly controlled, and all donors are screened for hepatitis B and C, and HIV, and blood is only imported from countries - mostly the USA - free of variant CJD. The chance of contracting a virus through anti-D has been estimated to be 1 in 10,000 billion doses.
Occasionally anti-D can cause a local reaction at the site of the injection or an allergic reaction in the mother, but these are rare. For this reason it is advisable to stay in the health centre or doctor's surgery for 20 minutes after having the injection.
Anti-D cannot harm your baby and the injection at 28 and 34 weeks is highly recommended. If, however, you decide against this, you will still need one if you have any bleeding in the later weeks of the pregnancy and again after delivery if the baby is found to be RhD-positive and you would like more children. If you are certain you will not be having any more children - maybe you are opting to be sterilised after this baby - or if you are in a stable relationship with the father of the child and it is certain he is also RhD-negative, then anti-D is not necessary. Your partner will not be tested routinely to find out his blood group, but he might already know this if, for example, he is a blood donor.
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