Introduction Maternal red cell alloimmunization to Rh antigen in pregnant women occurs when the immune system is sensitized by foreign red blood cell surface antigens, in this case fetal red blood cells, inducing an immune response. Various antigens of blood group systems may cause alloimmunization, especially the Rh, Kel, Fy, JK, and MNS systems. This study aimed to determine alloimmunization to the different frequencies of Rh antigen among pregnant women in South Western Uganda. Methods A total of 1369 pregnant women consented and were recruited into a cross-sectional study during their regular antenatal visits during the period August 2020 to July 2021. Samples (4 mL) of anticoagulated and coagulated blood were obtained, and Rh blood grouping including Rh antigen and the indirect antiglobulin test (IAT) was carried out using the agglutination technology of the LISS ID-Card technique in the Ortho Biovue ID-Micro Typing System. Results Out of 1369 participants recruited to the study, 78 (5.7%) were D − , 1291 were D + , and 134 (9.8%) had alloantibodies. Among those with alloantibodies, 115 (85.8%) were D + and 19 (14.2%) D − . The percentage alloimmunization according to the Rh antigens was highest in e (9.72%), c (2.48%), C (2.34%) and E (0.94%) antigens. With the ABO system, alloimmunization was highest in blood group B (10.7%), followed by A (10.6%), O (9.2%) and then AB (7.1%). Alloimmunization was more prevalent in D − (24%) than in D + participants (8.9%). Rhesus antigen e was the most prevalent antigen (99.8%), followed by c. The alloimmunization rate of 9.8% among these participants is high, and appears in both D + and D − women. The other Rhesus antigens are seen to cause alloimmunization, with antigen e causing the highest prevalence. In conclusion, there is a need to identify antibodies and study the outcome for clinical significance, especially in D + women, to facilitate proper pregnancy management.

Introduction ABO and Rh are the major blood group systems in Transfusion Medicine, the ABO system based on two red cell antigens (A, B) while the Rh has about 50 antigens of which five are highly clinically significant (D, C, c , E, e ). These vary among races and ethnic groups. Blood type phenotype incompatibility between mother and fetus may result in antigen mismatch, triggering alloimmunization, and thus causing hemolytic transfusion reaction (HTR), which results in hemolytic disease of fetus and newborn (HDFN). This study aimed to determine the frequencies of ABO and rhesus blood group antigen in the pregnant women in South Western Uganda. Methods A cross-sectional study was carried out on 1369 pregnant women who were recruited and provided consent to participate during their regular antenatal visits between August 2020 and July 2021. Four milliliters (4mL) of EDTA-anti-coagulated blood samples were collected and ABO and Rh-blood grouping including Rh antigen screening was done using the agglutination technology comprised of glass beads and reagent contained in a column of the Ortho Biovue ID Micro Typing System (Ortho Clinical Diagnostics, New Jersey, USA). The Rh antigen phenotypes and frequencies were then determined. Results There was percentage distribution of 99.8%, c 99.3%, D 94.3%, C 19.2% and E 15.9%, with Rh cDe/cDe (65.1%) being the most common phenotype followed by cDe/CDe (15%), cDe/cDE (10.8%) and cDE/cDE 0.1% least common. The ABO grouping frequency was obtained as O 49.4%, A 29.5%, B 17.0% and AB 4.1%, with D positivity at 94.3%. Discussion Population genetic variations result in varied expressions of red cell antigens that may have clinical complications. Knowledge of the presence of these Rh antigen distributions and phenotype frequencies during pregnancy help in rational management of the pregnancy, alloimmunization and better approach to safe blood transfusion.