Blood groups and rhesus (Rh) factor

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Blood groups and rhesus (Rh) factor

Being aware of the risks associated with rhesus incompatibility!

Everyone has a blood group ‘A’, ‘B’, ‘AB’, or ‘O’ and an Rh factor, which is either positive (Rh+) or negative (Rh-), depending on whether or not an antigen known as ‘factor D’ can be found on the surface of the red blood cells.

​What is the purpose of establishing someone’s blood group and Rh factor?

The child you are carrying will inherit your genetic characteristics and those of its father. Your baby’s blood group and Rh factor may turn out to be different to yours.

If foetal red blood cells pass into the mother’s bloodstream (which often happens during delivery), they will be recognised as foreign and induce both an immune reaction and the production of antibodies (irregular agglutinins). These antibodies will survive for a long time and, in the event of a later pregnancy, will pass through the placenta and potentially destroy foetal red blood cells (a process known as haemolysis), causing foetal anaemia (haemolytic disease of the newborn – HDN – or erythroblastosis fetalis).

Anticorps anti-Rh+

​This is my first pregnancy. Is there any risk?

The risk depends on your Rh factor and that of the baby’s father:

​*Notes: There are other forms of immunisation apart from those associated with Rh or anti-D factor (anti-E, anti-c, anti-C, anti-e, anti-Kell, etc.). These are rarer and generally less serious. The laboratory which determines your blood group will inform you about these and your doctor will explain what you need to do.

Fortunately, as the mother and foetus have separate circulatory systems, foetal red blood cells do not generally enter the mother’s bloodstream. At the time of delivery, however, the placenta becomes detached and agglutinogen D, carried by the Rh+ baby’s red blood cells, causes anti-D antibodies to form in the mother’s blood. This is of no importance at the time of a first pregnancy because the baby has already been born and is therefore safe from these antibodies.​​​​​​​

​Is there any risk from the second pregnancy onwards?

From the second pregnancy onwards, it is essential to measure antibody levels for the reasons described above. If screening is positive, the risk will generally depend on the antibody level and the higher this is, the greater the risk. If levels are low, pregnancy will tend to go full-term without any problems for the child (although jaundice is a possibility). If levels are high, the foetus will be in danger, which may result in miscarriage, premature delivery or foetal damage. In such cases, the gynaecologist will perform additional tests (ultrasound scans, amniocentesis) to assess the extent of any haemolysis and decide which treatment path to follow.​​​​​​​

​Is any preventive treatment available?

Prevention involves injecting an Rh-negative woman, who has just given birth to a Rhesus-positive baby but is not yet a carrier of anti-rhesus antibodies, with anti-D gammaglobulins (anti-rhesus antibodies, Rhophylac®). These gammaglobulins are antibodies that rapidly destroy foetal red blood cells that have passed into the mother’s bloodstream during delivery. The mother therefore has no time to develop her own antibodies. Thanks to this anti-D prophylaxis, the mother can have more rhesus-positive babies without any issues.

What needs to be done, in short?

​Before any pregnancy or during the first pregnancy.

It is useful to check whether or not you are already a carrier of irregular antibodies (you may have become one at the time of a miscarriage that went unnoticed).

​At the start of any new pregnancy

It is essential to screen for irregular antibodies again and repeat this during pregnancy. If you are Rh- and the father is Rh+, the laboratory will be able to determine the foetal Rhesus status by simply taking a sample of maternal blood. Talk to your gynaecologist about this.

​Following each delivery

An Rh- woman must be given an injection of anti-D serum. This anti-D prophylaxis must be administered following an ectopic pregnancy, miscarriage, termination of pregnancy, hydatidiform mole, abortion, vaginal bleeding, cerclage, choriocentesis, amniocentesis, abdominal trauma (such as a fall or traffic accident), or any other situation with a potential risk of the baby and mother’s blood becoming mixed together.