- By MLS Dogo Abdullahi Duniya

BACKGROUND OF ABO BLOOD GROUP

The original classification of the ABO system was made by Karl Landsteiner in 1900. The ABO system consists of four blood groups or phenotypes: A, B, AB and O. The two antigens, A and B are responsible for these four groups. If A antigen is present on the red cell, the individual is said to belong to group A. Those having B antigen are group B persons. Group AB individuals have both A and B antigens while group O persons have neither A and B antigens on their red cells.

The allelic genes A, B, and O, can be inherited in the ABO system. The following combination of allelic is possible: AA, AO, AB, BB, BO, and OO, resulting in AA, AB, BB, and O group individuals respectively. This is so because A and B genes are dominant and O gene is recessive

LAWS OF INHERITANCE OF ABO GROUPS

According to Bernstein’s theory, two laws of inheritance have been proved.

1 – It is not possible that an offering can possess antigen A, B or both unless it is inherited from one or both parents.

2 – A parent of blood group AB cannot produce an offspring of group O. Similarly, a parent of blood group O cannot produce AB offspring. The reason for this law is that group AB is heterozygous, and therefore A and B genes must come from two parents.

For antibodies in the serum, according to Landsteiner’s rule, corresponding antibodies cannot co- exist in the same person blood for example, persons who are blood group A cannot have antibodies to antigen A (anti A) in their blood and group B persons cannot have anti – B in their blood for ABO system. Hence a person of group A has anti B in serum, while a person of group B will have anti A and a person of group O will have both anti A & anti B in the serum and blood group AB will have neither antibody in their serum (blood).

ABO COMPATIBILITY AND COMPLICATION FOR CHILD BEARING

In terms of marriage individual from different blood groups can still have a healthy relationships and successful marriage. However, when it comes to child bearing, the compatibility of ABO blood group can affect the new born blood type. In rare cases incompatibility between the mothers’ and baby’s blood group can lead to complications such as haemolytic disease of the new born (HDN). Only group O individuals make antibody – A and antibody – B. Therefore, only A or B infants of group O mothers are at risk from ABO incompatibility. Although 25% of births are susceptible, only about 1% is affected; even then the condition is usually mild and very rarely severe enough to need exchange transfusion (about 1 in 3000). Two mechanism protect the foetus against anti-A and anti-B antibodes.

1. The relative weakness of A and B antigens at birth,
2. The wide spread distribution of A and B glyprotenis in body fluids and tissues, which diverts much of the lgG antibody that crosses the placenta away from the red cell target

ABO – HDN may be seen in the first incompatible pregnancy, because the group o primigravida has already made lgG anti-A and anti-B in response to various immunization stimuli. This is unlike anti-D HDN, where immunization usually takes place at the end of the first pregnancy, the first child being unaffected.

At birth, ABO –HDN is suspected if a group o mother has an A group or B group child who is Jaundiced. Also, the blood film of the affected child shows spherocytosis and reticulocytosis which are characteristic for the condition..

RHESUS (Rh) GROUP SYSTEM

BACKGROUND OF Rh SYSTEM

The discovery of the Rh system is based on the work by Landsteiner wiener in 1940 and by Levine and Stetson in 1939. In 1940, Landsteiner’s and wiener inoculated the red cells of rhesus monkeys into rabbits and guinea pigs. The resulting antibodies agglutinated the red cells of the monkeys and also of about 85% of the population. Those 85% were called Rh (Rhesus) positive because they possessed the same antigen that were present on the red cells of Rhesus monkeys. The rest of the population was called Rh- negative. It was that the antibodies to the same antigen can cause a haemolytic reaction. Unlike ABO antibodies there are no naturally occurring Rh antibodies. All Rh antibodies are ‘immune’ antibodies resulting from a specific antigenic stimulation e.g. transfusion, pregnancy or by injection of the antigen. 

RHESUS (Rh) HAEMOLYTIC DISEASE OF THE NEWBORN (HDN) 

Anti D caused the most severe form of HDN. This may occur during pregnancy and child birth when there is Rhesus (Rh) group incompatibility between partners. In other words, when a woman is Rh-negative and the man is Rh-positive, the baby may be Rh positive and there is a risk of Rh incompatibility between the mother and the baby, if the mother’s blood that is Rh-negative comes in contact with the baby’s blood (Rh-positive blood inherited from the father) - she may develop antibodies that can affect future pregnancies. This may lead to still birth or HDN of varying degree depending on the maternal dose of foetal red cells and the mother’s ability to respond to the antigenic stimulus. However, today this can be effectively managed by preventing the mother from becoming alloimmunised against the RhD antigens. This is done by administering | Rhogam Rh-immunoglobulin to Rh-negative women during pregnancy and after child birth to prevent the development of Rh-antibodies

It is a standard in antenatal care to determine the ABO and Rh (D) groups of all mothers and screen the serum for antibodies.

Ideally, an Rh-negative woman is supposed to marry an Rh-negative man. With this type of marriage all the offspring will be Rh-negative and there will be no foreign agent for sensitization of the mother to produce anti-D against subsequent pregnancies or babies. The challenge here however, is that Rh-negative individuals are very few in the society to make this type of marriage possible. As a result, majority of the Rh-negative women will end up marrying Rh-positive men. Hence the risk of haemolytic reaction occurring. 

Anti D is now administered to every RhD-negative mother giving birth to an RhD-positive child, provided she is not already immunized to the D antigen by previous pregnancy or blood transfusion. It is important that the dose of anti-D given should be adequate to clear all the foetal red cells from the maternal circulation. and the appropriate dose of anti D should be given as soon as possible after delivery and not later than 72 hours post partum. In case of abortion, it is assumed that the foetus is Rh (D) positive (unless the father is also Rh negative) and anti- D should also be given.

Any event during pregnancy which might lead to a transplacental bleed (e.g. trauma, obstetric manipulation, amniocentesis, should be covered by an appropriate injection of anti-D. This treatment helps to protect mother against future pregnancies from potential implication related to Rh-incompatibilities.

In conclusion, it is important for couples with Rh group differences to seek guidance from health care providers before planning for pregnancy especially, when the woman is Rh negative and the man Rh positive. Regular prenatal care and monitoring are essential to ensure the health and wellbeing of both mother and the baby.

REFERENCES:

Ochei, J. and Kolhatkar, A.: Medical laboratory Science: Theory and Practice (2007)

Cawkey, J.C. and MCNICOOL, G.P.: Integrated Clinical Science Hachmatology (1983)

www.ncbi.nlm.nih.gov/pmc/articles

www.mayoclinic.org/diseases.conditions/infantjaudic/diagnosis-treatment

MLS Dogo Abdullahi Duniya, FUL Health Corner, Federal University Lokoja