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Rhesus negative blood group - 'anti-D' injection

Rhesus negative blood group - 'anti-D' injection


'Anti-D' injection

About 15% of women have a 'Rhesus negative' blood group or 'Rhesus factor' (being 'A negative', 'B negative', 'AB negative' or 'O negative'). If a woman has a negative blood group and she miscarries (or is threatening to miscarry with heavy bleeding during early pregnancy), she may require an injection of 'anti-D immunoglobulin' within 72 hours after the miscarriage (or within 72 hours after the bleeding has commenced for a threatened miscarriage).

Anti-D immunoglobulin is aimed at preventing the woman from developing antibodies in her blood stream (also known as agglutinins'). It is possible for this to happen if a woman with a 'negative' blood group conceives a baby with a 'positive' blood group. The incidence of a woman developing antibodies through miscarriage is thought to be up to 7% if the miscarriage occurs during the first 13 weeks of the pregnancy and up to 20% for miscarriages after 13 weeks.

NOTE:Women with a 'Rhesus positive' blood group ('A positive', 'B positive', 'O positive', 'AB Positive') do not have this health concern because it does not matter what blood group their baby is.

When a woman becomes pregnant, her first pregnancy visit will usually involve some routine blood tests . One of the standard tests performed is called a 'group and antibodies'. This test identifies the woman's:

  • Blood group. Your blood group will be either A, B, O or AB.
  • 'Rhesus factor'. This will be either 'positive' or 'negative'.
  • Antibodies (also known as 'agglutinins'). If everything is normal, your blood should NOTcontain any antibodies. The result of the antibody test is often written as 'nil detected' or 'negative'.

The test results are recorded on the woman's pregnancy record card and are generally written as 'A Negative' (or 'A Neg'), 'O Positive' (O Pos), 'B Negative' (B Neg), A Positive (A Pos) or 'AB Negative' (AB Neg) and so on. As mentioned before the antibodies (or 'agglutinins') will be written as 'nil detected' or 'negative'. You can read more about this in tests offered during pregnancy.


NOTE:Miscarriages often happen before the woman has been able to have her first routine blood tests for pregnancy. A 'blood group and antibody' blood test may be something that the doctor performs once a miscarriage becomes apparent. You may already be aware of your blood group from a previous pregnancy, or because you have donated blood at the blood bank.

During pregnancy, the baby's and mother's blood remain completely separate, with all the nutrients and oxygen passing over a fine membrane at the level of the placenta. It is very rare for the mother's and baby's blood to mix. However, under certain circumstances it is possible for a very small amount of the baby's blood to cross over into the mother's blood stream. This can happen:

  • During bleeding with a miscarriage (or with an operation to remove the miscarried pregnancy).
  • With an ectopic pregnancy.
  • With heavy bleeding during early and late pregnancy.
  • After the birth of the baby as the placenta separates. You can read more in Negative blood group - the birth.
  • During medical procedures that can cause minor bleeding inside the uterus such an as amniocentesis or CVS.

If the baby's blood is 'Rhesus positive' and some of their blood passes into their mother's system (who is 'Rhesus negative'), it is possible for this transfer of blood to trigger a 'reaction' in the mother's blood to form 'antibodies'. The formation of antibodies is a normal physical response. Antibodies 'fight' substances that our bodies interpret as being 'foreign invaders' to our system. The antibodies that form in the mother's blood stream are trying to 'get rid' of the 'foreign' baby blood. (This natural 'reaction' is similar to the one we intentionally produce when we immunise our bodies against disease.)

NOTE:If the baby's blood is 'negative' (like the mother's) no reaction will occur. However, unless the miscarriage is late (after 14 weeks) it is unlikely that any test will be able to determine exactly what the baby's blood group and Rhesus factor are. This means the caregiver will presume the baby is 'positive', taking a precautionary view and treating the woman accordingly. It is estimated that about 60% of babies will be 'positive' and about 40% will be 'negative'. You can read about the chances of your baby having a 'positive' or 'negative' Rhesus factor and how the father's blood group can play a role in Negative blood group - the birth.

The formation of Rhesus antibodies does not affect the health of the woman. The antibodies simply stay dormant in the woman's system 'waiting' in case they are needed for a further 'invasion' of positive blood cells (which can happen with a future pregnancy). If she becomes pregnant again, and the subsequent baby also has a 'Rhesus positive' blood group, the antibodies in the mother's blood will become reactivated, crossing the placenta to react with the new baby's blood.

When antibodies enter the new baby's blood stream it can cause a process called 'alloimmunisation' or 'isoimmunisation'. This can result in a miscarriage of that baby, or the pregnancy may continue with the baby developing a condition called 'Rhesus haemolytic disease' or 'Rhesus isoimmunisation'. This condition usually causes varying degrees of anaemia and jaundice in the baby, either while still growing in the uterus or soon after they are born. The treatment usually involves blood transfusions (sometimes while they are still growing in the uterus) and after birth they will need to be cared for in the intensive care nursery. You can read more in Rhesus haemolytic disease.

'Anti-D' injection.

Anti-D immunoglobulin is given as an injection. Essentially it is a component of donated blood, harvested from people who have already developed antibodies against 'positive blood'. It aims to prevent the formation of Rhesus antibodies in a woman's blood stream, in case any of the baby's blood has passed into her system. This will hopefully avoid health problems in relation to Rhesus isoimmunisation for future pregnancies. (In most cases, the blood group and Rhesus factor of the miscarried baby will be unknown. However, the injection will be recommended just in case the baby is 'positive'.)

The anti-D immunoglobulin injection needs to be given within 72 hours after the heavy bleeding starts or after an operation to remove the miscarried pregnancy. One injection of anti-D immunoglobulin will cover the woman for about 3 months. Therefore if the injection is given because the woman has bleeding associated with a threatened miscarriage, but the pregnancy continues and further bleeding happens a few weeks later, the injection will not need to be repeated. You can read more on anti-D immunoglobulin in Negative blood group - the birth.

At present, the use of 'anti-D immunoglobulin' and how effective it is in stopping the production of Rhesus antibodies in relation to miscarriage remains unclear. We do know that for women who go on to have a baby and have the anti-D injection after the birth, the likelihood of them developing antibodies is greatly reduced from about a 10% to 20% chance to about a 0.2 to 1.5% chance. (Be aware that an injection of anti-D immunoglobulin does not guarantee you will not produce Rhesus antibodies, but it does greatly reduce the chances.)

It is thought that miscarriages less than 6 weeks gestation are highly unlikely to involve the baby's blood transferring to their mother and therefore will not result in the formation of antibodies (unless the pregnancy is ectopic). For threatened miscarriages, spontaneous miscarriages, ectopic pregnancies, induced miscarriages and miscarriages that involve the doctor preforming an operation after 6 weeks (or the intentional termination of a pregnancy), the chances of the woman forming antibodies are estimated to be about 6-7%. For any miscarriages after 13 weeks, it is thought to increase to about 20%.

Last revised: Friday, 27 June 2014

This article contains general information only and is not intended to replace advice from a qualified health professional.

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