Anti-D injections are offered to all pregnant woman who have a rhesus-negative (RhD-negative) blood group to prevent the possibility of the blood disorder RhD haemolytic disease of the newborn.

Please note: there is a newer article about Anti-D injections (click here to view).

Understanding the medical terms and the details of this disorder and it’s prevention can seem rather complicated. But, as with any medical recommendation made during pregnancy, having plenty of information allows you a greater degree of clarity and confidence in your health choices and the decisions that you make. Below I look at some of the most frequently asked questions relating to this topic.

What are rhesus negative and rhesus positive blood types and how are they important to my pregnancy?

There are two main systems used for categorising human blood: the ABO and the Rhesus (Rh) system. Individuals who are Rhesus (Rh) positive have a particular protein (RhD antigen) attached to their red blood cells whereas individuals who are Rhesus negative do not. There is a higher probability that you are RhD positive — approximately 85% of Caucasians are RhD positive and only 15% are RhD negative (lower still in other ethnic groups). Whether or not you are Rh positive or negative depends on the 2 rhesus genes you inherited from your parents (we receive 1 gene from each parent that may be either positive or negative). If you are RhD negative and pregnant, there is a chance that your baby could be RhD positive. In a first pregnancy, 60% of Rhesus negative mothers will have an RhD positive child. When this occurs there is the possibility for complications.

What can happen if I have a different rhesus blood group to my baby?

Having a different rhesus blood group to your baby is only a potential problem if you are RhD negative and your baby is RhD positive. This is because your baby’s red blood cells have the RhD antigen attached to them whereas yours do not. If small amounts of your baby´s blood mixes with yours during pregnancy, your immune system may perceive this difference in blood types as a threat, producing antibodies that will ‘fight’ against your baby’s blood. This process is called sensitisation or alloimmunisation, and once your body has made these antibodies they cannot be removed. It is important to note that this process is unlikely to affect your current baby, but instead becomes a problem if you have subsequent babies that are RhD positive. This is because the process of producing antibodies takes time. The initial antibodies you produce in your first pregnancy (IgM) cannot cross the placenta but the subsequent antibodies produced in later pregnancies (IgG) can.

If I am RhD negative with an RhD positive baby, how likely am I to produce antibodies against my baby’s blood?

The most likely times you would produce antibodies is when an exchange of blood between you and your baby is most likely: at delivery, after abortion or after an invasive procedure. In a 2006 review of RhD testing, the authors state that without preventative treatment,

5-15% of RhD negative pregnant women will develop antibodies at delivery; 3-6% after spontaneous abortion; and 2-5% during amniocentesis. If no ´high risk´ situations occur prior to delivery , without treatment 1-2% of RhD negative pregnant women will produce antibodies before birth due to haemorrhages of their baby´s blood (SAFE WP6, University of Warwick 2006).

What is Rh D haemolytic disease of the newborn?

If your body has produced antibodies to fight the antigens on your baby´s red blood cells a blood disorder called RhD haemolytic disease of the newborn (sometimes called Rhesus disease or Rh disease) can result. It is important to realise that if you have produced antibodies, this will not necessarily lead to haemolytic disease of the newborn. If it does, it can be life-threatening, manifesting as anaemia, jaundice, heart or liver problems, or mental retardation. Before any preventative treatment had been developed haemolytic disease of the newborn affected 1% of babies in second pregnancies born to RhD negative women in England and Wales (SAFE WP6, University of Warwick 2006)

What are Anti-D injections and when are they recommended?

Anti-D injections are given to pregnant women who are RhD negative as a means of preventing antibodies from forming. The injections are derived from donor human blood and are tested for hepatitis C and B, parovirus B19 and HIV. The active substance in these injections is human anti-D immunoglobulin and other ingredients can include human albumin, glycine and sodium chloride. Fortunately since 2001 anti-D injections no longer contain thiomersal which is mercury derived. In 2008 the National Institute for Health and Clinical Excellence (NICE) published guidelines recommending that that one dose of anti-D be administered between weeks 28 and 30 of gestation.

Are the anti-D injections safe?

Anti-D injections have been used for approximately 40 years and have been considered to be safe. However because anti-D injections are derived from human plasma there continues to be a risk that viruses can be transmitted to pregnant women receiving them. This occured in the 1970’s in Ireland and could potentially occur again with diseases for which there are no tests available. In regards to the other ingredients in anti-D injections, drug manufacturer Pfizer states that sodium chloride safety in pregnancy has not been established. UK Government-based web information include the following side effects of anti-D injections of unknown frequency: allergic or anaphylactic, urticaria, tightness of the chest, wheezing, breathing difficulties or shock, chills, faster heart rate, fever, general feeling of being unwell, headaches, injection site problems such as pain or tenderness, lowered blood pressure, may affect the results for certain tests, nausea, skin problems, vomiting.

Will I need the anti-D injection?

Rh D haemolytic disease of the newborn is only relevant to RhD negative pregnant women because of the chance that they may have an RhD positive baby. If you are RhD negative and are certain of paternity, then a paternal blood test can be conducted. If both you and your partner are RhD negative then it is not possible for your baby to be RhD positive and you will not need to have anti-D injections. There is also non-routine testing that has developed called non-invasive prenatal diagnosis (NIPD) where your baby’s RhD status is assessed. The accuracy of this testing has been reported as between 94.8% -100%.

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Please note: there is a newer article about Anti-D injections (click here to view).

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