Anti D Prophylaxis

Anti D Prophylaxis
What is anti-D prophylaxis?
Prophylaxis is the word given to a medicine that is used to prevent something happening. Anti-D prophylaxis means giving anti-D immunoglobulin to prevent a woman producing antibodies against RhD-positive blood cells and so to prevent the development of HDN in an unborn baby.
Anti-D immunoglobulin is made from a part of the blood called plasma that is collected from donors. The production of anti-D immunoglobulin is very strictly controlled to ensure that the chance of a known virus being passed from the donor to the person receiving the anti-D immunoglobulin is very low – it has been estimated to be 1 in 10,000 billion doses.
Routine antenatal anti-D prophylaxis (RAADP) is given by injection to pregnant women who are RhD negative usually at week 28 of their pregnancy. After the birth, a blood sample will be taken to test the baby’s blood group. If the baby is RhD positive, a mother who is RhD negative will be given a further injection of anti-D immunoglobulin – this is known as postnatal anti-D prophylaxis. If an RhDnegative woman has a potentially sensitising event DURING THE pregnancy she will be offered anti-D prophylaxis at the time of the event: this is known as antenatal anti-D prophylaxis or AADP.
Occasionally anti-D prophylaxis causes allergic responses in the mother, but these are rare.
What does RhD negative mean?
The rhesus factor is found in the red blood cells. People who are rhesus positive have a substance known as D antigen on the surface of their red blood cells – they are said to be RhD positive. People who are rhesus negative do not have the D antigen on their blood cells – they are RhD negative.
Whether a person is RhD positive or RhD negative is determined by their genes – that is, it is inherited from a parent.
Why does RhD status matter?
RhD status matters if a woman who is RhD negative becomes pregnant with a baby who is RhD positive. This can only happen if the baby’s father is RhD positive – but not all children who have an RhDpositive father will be RhD-positive, because the father may have both RhDpositive and RhD-negative genes. If any of the blood cells from a RhDpositive baby get into the blood of a RhDnegative woman, she will react to the D antigen in the baby’s blood as though it is a foreign substance and will produce antibodies.
This is not usually dangerous in a first pregnancy, but in later pregnancies the antibodies in the mother’s blood can cross the placenta and attack the blood cells of a RhD-positive unborn baby.
This can cause ‘haemolytic disease of the newborn, which is also known as HDN. HDN can be very mild and only detectable by laboratory tests. But it can be more serious and cause the baby to be stillborn, severely disabled or to die after birth as a result of anaemia (lack of iron in the blood) and jaundice.
Each year in Ireland there are about 5000 births of RhD-positive babies to RhDnegative women. In Ireland about 50 babies develop HDN each year, and must be closely monitored. Each year between 2-5 babies die from HDN. A further 10 children each year will have developmental problems as a result of HDN.
The most common time for a baby’s blood cells to get into the mother’s blood is at the time of birth. But it can happen at other times, for example during a miscarriage or abortion, or if something happens during the pregnancy such as having an amniocentesis, chorionic villus sampling, vaginal bleeding or external cephalic version (turning the baby’s head down).
An event that could cause the mother to produce antibodies against the D antigen is called a ‘potentially sensitising event’.
Recommendations for RAADP
If you are pregnant and are RhD negative you should be offered RAADP if you have not already been ‘sensitised’, this means that you have already have antibodies to the D antigen in your blood that can be detected by a blood test at the beginning of your pregnancy.
If you are pregnant and are RhD-negative, your midwife, obstetrician or GP (that is, whoever is responsible for your antenatal care) should discuss RAADP with you and explain the options available so that you can make an informed choice about treatment. The difference between RAADP and AADP should be clearly explained to you.
The healthcare professional should discuss the situations where anti-D prophylaxis would be neither necessary nor cost effective. Such situations might include those where a woman:
• has opted to be sterilised after the birth of the baby
• is in a stable relationship with the father of the child, and it is certain that the father is RhD negative
• is certain that she will not have another child after the current pregnancy.
• You should be offered RAADP even if you have already had AADP for a potentially sensitising event earlier in your pregnancy. You should be offered postnatal anti-D prophylaxis whether or not you have had AADP or RAADP.
Recommendations for Prophylaxis Anti D for Medical Management and or Surgical Management of Miscarriage
Following administration of medications and /or following surgical management you will be offered Anti-D.
Other situations for Anti D prophylaxis:
• Ectopic pregnancy
• All miscarriages over 12 weeks including threatened
• All miscarriages where the uterus is evaluated surgically
• For threatened miscarriage under 12 weeks, if bleeding is heavy or associated with pain.

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