RED CELL ISO-IMMUNISATION
It is mean the production of antibodies in response to isoantigens which are present on erythrocytes
Maternal iso-immunisation occurs when the immune system of the mother is in sensitized to antigens on fetal erythrocytes, lead to production of IgG antibodies.
In subsequent pregnancies, these antibodies can cross the placenta and can attack the fetal red cells – and leading to hemolysis and anemia (known as hemolytic disease of the newborn).
In this report, we should look at the pathophysiology of red blood cell iso-immunization, how it is screened for, and how it is prevented during pregnancy.
PATHOPHYSIOLOGY
In red blood cells iso-immunisation , maternal antibody is formed in response to surface antigen on fetal erythrocyte. It occurs when the fetal cell enter the maternal circulation via a (sensitizing event ) – such as an antepartum hemorrhage or abdominal trauma. It can also occur during delivery.
There are rarely any problems during the primary exposure for these antibodies. However, in subsequent pregnancies, maternal antibodies can cross the placenta and attack the fetal red cells in vessels (if they carry the same surface antigen). These will lead to hemolysis and subsequent fetal anemia.
There are more than 50 different surface antigens capable of inducing maternal iso-immunisation. The most common group is the Rhesus D blood group – for those individuals which are either positive ( RhD+ ) or negative ( RhD- ) .
Rhesus D iso-immunisation is possible only in (RhD-) women, and occurs when they come into contact with the blood of a (RhD+) fetus:
A woman is (RhD-), and her partner is (RhD+). She will pregnant with a fetus which is also (RhD+). During childbirth, she will come into contact with the fetal (RhD+) blood, and antibodies are produced inside mother’s vessels (known as anti-D antibodies).
- The mother later becomes pregnant with a second child that is also (RhD+).
- The woman’s anti-D (RhD+) antibodies will cross the placenta during the second pregnancy and enter the fetal circulation, which contains (RhD+) red blood cells. They will bind to the fetus’ (RhD) antigens on its red blood cells surface membranes.
- This will cause the fetal immune system to attack and destroy its own red blood cells, leading to fetal anemia. This is known as hemolytic disease of the newborn (HDN).
Anti-D Immunoglobulin
If a sensitizing event happens, maternal iso-immunization can be stopped via the administration of Anti-D immunoglobulin injection. It binds to any (RhD+) red blood cells in the maternal circulation, and there is no immune response is stimulated. YOU SHOULD KNOW THAT: Anti-D immunoglobulin is never required in ( RhD+) mothers, as well as they cannot generate anti-D antibodies.
RECOMMENDATION
Antenatal prophylaxis with anti-D immunoglobulin in non-sensitized Rh-negative (RhD-) pregnant women at 28 and 34 weeks of gestation to prevent RhD allo-immunisation is only recommended in the context of rigorous research.
INDICATION OF Anti – D IMMUNOGLOBULIN INJECTION:
If Rhesus D negative women, the administration of anti-D immunoglobulin should be considered the following any sensitizing event:
- invasive obstetric testing (for example amniocentesis or chorionic villus sampling)
- Antepartum hemorrhage (APH)
- Ectopic pregnancy
- External cephalic version
- Fall down or abdominal trauma or injury
- Intrauterine death
- Miscarriage
- Termination of pregnancy
- Delivery (SVD, instrument or caesarean section)
DIAGNOSIS
Rhesus disease (RhD) is usually diagnosed throughout the routine screening tests you’re offered during pregnancy.
BLOOD TESTS
A blood test shall be carried out early on in pregnancy to test for conditions such as anemia, rubella, HIV and hepatitis B.
The blood should also be tested to determine the group of the blood, and whether the blood is (RhD+) or (RhD-).
If the (RhD-), the blood should be checked for the antibodies (known as anti-D antibodies) that destroy (RhD+) red cells. The mother should become exposed to them during pregnancy if the baby has (RhD+) red blood cells.
If there are no antibodies in the mother’s circulation, the blood should be checked again at 28 weeks of pregnancy and the mother should be offered to take anti-D immunoglobulin injection to reduce the risk of the baby to developing rhesus disease.
If anti-D antibodies are detected in mother’s blood during pregnancy, there is a risk that the unborn baby will be affected by rhesus disease. And because that, the mother and the baby should be monitor more frequently than usual during mother’s pregnancy.
In some cases, a blood test to check the father’s blood type may be offered if the mother has (RhD-) blood cells. This is because the baby won’t be at risk of rhesus disease if both the mother and father have (RhD-) blood cells.
CHECKING THE BABY’S BLOOD TYTPE
It is possible to determine if an unborn baby is (RhD+) or (RhD-) by taking a simple blood test during pregnancy.
The (DNA) from the unborn baby can be found in the mother’s blood cells , which enables the blood group of the unborn baby to be tested without any risk. It is usually possible to get a trustworthy result from this test after 11 to 12 weeks of pregnancy, which is long before the baby is at risk from the antibodies.
If the baby is (RhD-), they are not at risk of developing rhesus disease and no extra monitoring or treatment needed. If they are found to be (RhD +), the pregnancy should be monitored more closely so that any problems that may occur can be treated quickly.
In the future, (RhD-) women who haven’t developed anti-D antibodies may be offered this test routinely, to know if they are carrying an (RhD-) or (RhD+) baby, to avoid unnecessary treatment.
MONITORING DURING PREGNENCY
If the baby is at risk of developing rhesus disease, they will be monitored by measuring the blood flow in their brain. If the baby is affected, their blood may be thinner and flow more quickly. This can be measured using an US called a Doppler US.
If a Doppler US shows the baby’s blood is flowing faster than normal, a procedure called fetal blood sampling (FBS) can be used to check if the baby is anemic or not. This procedure involves inserting a needle through the mother’s abdomen (tummy) to remove a small sample of blood from the baby. The procedure is performed under local anesthetic, usually on an outpatient basis, so the mother can return to her home on the same day.
There is a small (approximately 1-3%) chance that this procedure could cause the mother to lose her pregnancy, so it only should be carried out if necessary.
If the baby is found to be anemic, they can be taken a transfusion of blood through the same needle. This is called an intrauterine transfusion (IUT) and it may require an overnight stay in hospital.
FBS and IUT are only carried out in specialist units, so the mother may need to be referred to a different hospital to the one where you are planning to have the baby.
DIAGNOSIS THE NEWBORN
If the mother’s RhD is (RhD-), blood should be taken from the baby’s umbilical cord when they are born. This is to check their blood group and see if the anti-D antibodies have been passed into their blood. This is called a Coombs test.
If the pregnant mother known to have anti-D antibodies, the baby’s blood should also be tested for anemia and jaundice.
PREVENTION
Rhesus disease can be prevented by having an injection of a medication called anti-D immunoglobulin.
REFERENCES
- 3.
TeachMe WHO https://www.nhs.uk/conditions/rhesus-disease/prevention/
ObGyn