Red cell alloimmunization in RhD positive pregnant women and neonatal outcome

The frequency of red blood cell (RBC) alloimmunization in RhD positive pregnant women is not known in our population. We planned to determine its frequency and correlation with neonatal outcome. We included 1000 RhD positive pregnant women: 500 had 'normal pregnancy' (Group I) and another 500 had 'high risk pregnancy' (Group II). ABO and extended Rh phenotyping were done by tube technique, antibody screening and identification by gel technique. For alloimmunized women, the paternal and neonatal ABO and extended Rh typing were done. Neonatal direct antiglobulin test (DAT) was also done and their clinical outcome observed. The frequency of RBC alloimmunization was 0.7% (7/1000) and all these women were from group II (p = 0.015). The alloantibodies were anti-E (85.7%), anti-c (71.4%), anti-Cw (14.3%) and anti-S (14.3%). Also, 6 women had history of transfusion (p < 0.01). Of the 7 neonates born to alloimmunized mothers, 4 (57.14%) had a positive DAT. The mean duration of phototherapy was higher in the DAT positive neonates (p < 0.01) and 2 (50%) required exchange transfusion. Thus, the frequency of alloimmunization was 0.7% in RhD positive pregnant women. High risk pregnancies and antenatal patients having a history of blood transfusion should be considered for regular antibody screening.