Maternal red-cell alloimmunization occurs when a woman's immune system is sensitized to foreign red-blood cell surface antigens, leading to the production of alloantibodies. The resulting antibodies often cross the placenta during pregnancies in sensitized women and, if the fetus is positive for red-blood-cell surface antigens, this will lead to hemolysis of fetal red-blood cells and anemia. The most severe cases of hemolytic disease in the fetus and newborn baby are caused by anti-D, anti-c, anti-E and anti-K antibodies. There are limited data available on immunization rates in pregnant women from Turkey. The aim of the present study was to provide data on the frequency and nature of maternal RBC alloimmunization in pregnant women in a tertiary care hospital. In this study, we retrospectively evaluated the indirect antiglobulin test results of Rh-negative pregnant women performed in our Blood Bank between 2006 and 2012. Indirect antiglobulin test positive women also underwent confirmatory antibody screening and identification. During the study period, 4840 women admitted to our antenatal clinics. With regards to the major blood group systems (ABO and Rh), the most common phenotype was 0 positive (38.67%). There were 4097 D-antigen-positive women (84.65%) and 743 women with D-antigen-negative phenotype (15.35%). The prevalence of alloimmunization was found to be 8.74% in D-antigen negative group. Despite prophylactic use of Rh immunglobulins, anti-D is still a common antibody identified as the major cause of alloimmunization in our study (anti-D antibody 68.57%, non-D antibody 31.42%). While alloimmunization rate to D antigen was 6.46%, non-D alloimmunization rate was 2.69% among Rh-negative pregnant women. Moreover, detailed identification facilities for antibodies other than anti-D are not available in most of centers across Turkey. However, large-scale studies on pregnant women need to be done in order to collect sufficient evidence to formulate guidelines and to define indications for alloantibody screening and identification. (C) 2013 Elsevier Ltd. All rights reserved.