Q: I am O positive and my fiancé is B positive. I am 4 months pregnant and the doctor says that my ICT level is positive (1 in 4 dilution) but my Rh is also positive. Does this normally happen? Is this situation bad for my baby? How does this affect my baby? Is there any cure for this situation? Please suggest.

A:There are about 20 known blood group systems that consist of over 200 antigens. Only two of these, however, (the ABO and the Rh) can commonly cause haemolytic transfusion reaction (HTR) as well as haemolytic disease of the newborn (HDN). A and B (& H) are antigens (proteins) found on the surfaces of red blood cells (and some other tissues). The ability to form these antigens on the surfaces of red blood cells is governed by genes inherited from parents. The pattern of genes we have is called genotype and the form in which it is expressed is called phenotype. It is the genotype (genetic make-up) which decides what the blood group (phenotype) will be. There are four possible blood groups in the ABO system: AB, A, B and O. Blood group A individuals possess A antigen on their red cells and have naturally occurring antibodies (anti-B) in their serum that react with group B and AB people. Blood group B individuals possess B antigen on their red cells and have naturally occurring antibodies (anti-A) in the serum that react with group A and AB people. Individuals with group AB possess both A and B antigens on their red cells and produce no naturally occurring antibodies. Finally, individuals with group O have neither A or B antigens on their red cells and have naturally occurring antibodies (anti- A and anti - B) in their serum that react with red cells from group A, B and AB people. In the ABO system there are three alleles: Ia - producing the antigen A, Ib - producing the antigen B and Io - producing neither antigen. IA and IB are co-dominant i.e. if both alleles are present, both antigens (A and B) will be formed on the surfaces of red blood cells and the individual will have blood group AB. Io is recessive and produces neither antigen and thus an individual will have blood group O if two of these alleles are present. The genotypic make-up can have 6 possibilities: Ia Ib (AB), Ia Ia (A), Ia Io (A), Ib Ib (B), Ib Io (B), Io Io (O) If either parent has group AB it will not be possible for any of the children to inherit Group O. If both parents have group O, all their children must have Group O and if both parents belong to blood group A (or B), it is still possible for some of their children to have Group O. Antibodies anti-A and anti-B are present in the blood of those who lack the corresponding antigen. These antibodies attack the red cells bearing them leading to anaemia and they can be detected by indirect antiglobulin (Coombs) test. ABO incompatibility can be life-threatening in case of mismatched transfusion but haemolytic disease of the newborn is usually mild. This is so as the amount of antibodies in mother's serum is low, the ABH antigens are not well developed in the newborn and the presence of ABH antigens in other tissues of the body. HDN can develop in non-O blood group babies of O-mothers.