RH factor

Blood Groups have a +ve or -ve appended to them. For example O+ve or O-ve. What does this +ve or -ve signify and whar relevance does it have on our health.

The +ve or -ve refers to the presence or absence of two Rhesus genes called the D or d which are inherited from each parent. A person is Rh(D) -ve if he/she has got a d gene from each parent making them d/d. A person is Rh(D) +ve if he/she has got D gene from each parent making them D/D or a D and d from the parents (either ones) making them D/d or d/D. Thus it is possible to have a Rh(D) -ve child from a father who is Rh(D)+ve and mother who is Rh(D) -ve. If the father has both a D and d gene; the offspring may inherit the d gene and shall be Rh(D)-ve if the mother is also Rh(D) -ve. The child from a D/D father and D/d or d/d mother will always be Rh(D) +ve since it will get a D from the father and either a D or a d from the mother. The d gene is not relavant. What is the presence or absence of the D which will make a person Rh(D) +ve or Rh(D) -ve.

All this is fine. The problem is that the Rh(D) +ve blood contains the D antigen which stimulates the Rh(D) -ve blood into producing antibodies against it.. A Rh(D) +ve woman would never produce an antibody against a Rh(D) -ve child, as +ve blood does not produce anti-d – there is no anti-Rh(d). However the problem comes where the mother is Rh(D) -ve while the child is Rh(D) +ve.

Erythroblastosis faetalis is one form of Rhesus disease. Red blood cells from the baby’s blood stream may enter the blood stream of the mother across the placenta, which cause the mother to make antibodies to the baby’s Rh factor. These antibodies cross the placenta and destroy the baby’s red blood cells. This destruction causes the baby to become anaemic and it can die before birth. If the baby does not die before birth, its bone marrow produces extra red blood cells which are immature and releases these into the baby’s blood steam. The haemoglobin from the broken down red blood cells breaks down into bilirubin, which is released into the mother’s blood stream across the placenta and cleared through her metabolism. But, after the baby is born, the bilirubin builds up in it’s blood stream, causing kernicterus, which is a syndrome characterised by poor feeding, poor body tone, seizures and poor breathing which may result in death. Hydrops faetalis is another form, also resulting from breakdown of red blood cells due to Rh incompatibilites, causing severe anaemia before birth. The baby is born swollen with a large liver, an enlarged heart and fluid on the lungs and in the tummy.

In such cases prevention is to be exercised. A blood test should be done at the start of pregnency to determine the D factor of the mother. If it is a Rh(D) -ve mother, further tests will be performed throughout the pregnancy to ensure that her blood is not producing Rh antibodies against her baby`s blood. If a bleed from the placenta should occur at any time during pregnancy and the foetal blood is Rh(D) positive, this would result in antibodies being produced. This is why it is essential to keep a note of when blood tests are due and what the results are.

Further she should be treated with a dose of anti-Rh antibody at about 28 weeks of pregnancy. This would help to prevent antibodies being produced if an unsuspected placental bleed were to then occur, or had already occurred within the preceding 72 hours of the injection. If this has not been done, then the mother should receive an anti-Rh gamma globulin within 72 hours of delivery. This way, the blood cells are destroyed before the three days are up and her own immune system is not provoked into producing its own anti-Rh(D).

It is highly recommended that an anti-D injection be given after any incident which could result in red Rh(D) positive cells becoming present in the mother`s bloodstream, whether this be medical intervention where Rh(D) blood has been used, a fall which may cause a placental bleed, or a miscarriage.

If the baby is born with either of the above two Rh diseases, then exchange transfusion, where equal amounts of blood are put in and taken out, is performed. Exchange transfusions can also be carried out before birth while the baby is still in the womb, if measurements of bilirubin in the amniotic fluid are becoming dangerously high.