Risk of maternal alloimmunization in Southern Pakistan – A study in a cohort of 1000 pregnant women

BackgroundHaemolytic disease of the fetus and the newborn [HDFN] is caused by incompatibility of maternal and fetal erythrocytes. Red blood cell alloimmunization is a well-known cause of HDFN. Due to heterogeneity of populations, the spectrum of alloimmunization varies around the world. This study aimed to determine the frequency of alloimmunization in pregnant women and to determine the risk of HDFN in our population.Study Design and MethodsThis was a descriptive study conducted at Aga Khan University Hospital Karachi. Blood type and red cell antibody screening was determined on every pregnant woman at her first antenatal visit. Red cell antibody identification was performed on positive screening results.ResultsA total of 1000 pregnant females including 633 (63.3%) multigravida were studied. Blood type B was predominant (n = 374 or 37.4%) and D negative was observed in 136 women (13.6%). No red cell antibody was detected in 982 females (98.2%). 20 red cell antibodies were detected in 18 women (1.8%). The incidence of non-anti-D was 16/1000 [1.6%] in all pregnant females. The non-anti-D alloantibodies included anti-M (n = 3; 15%), anti-Lewis(a) (n = 3; 15%), anti C ( n = 1; 5%), anti-E (n = 1; 5%), anti-e (n = 1; 5%), anti-Lewis(b) (n = 1; 5%) and nonspecific antibodies (n = 6; 30%). The incidence of anti-D was 4/136 or 2.9% in D negative blood type. After excluding prior sensitization due to blood transfusions, risk remained was 2.2%. Antibodies of clinical significance were identified in 9 (0.9%) females.ConclusionsIn our cohort, frequency of red cell alloimmunization during pregnancy was 1. 8% out of which 0.9% were clinically significant antibodies posing a risk for HDFN. Despite prenatal and post natal prophylaxis, risk of sensitization with D antigen in D negative women was high at 2.2%. We recommend that all pregnant women should be screened for irregular antibodies irrespective of the rhesus type.