INTRODUCTION: Rh immunization is one of the most serious complications in pregnancy due to the presence of antibodies in the blood of pregnant women and is RhD negative whereas the fetus is RhD positive. Antibodies pass through the placenta and bind to fetal erythrocytes, causing their destruction and decomposition (hemolysis). Destruction and disintegration of fetal erythrocytes cause fetal anemia and an increase in bilirubin. AIM: The objective of this study is examine the frequency of Rh immunization and determine the antibodies which were the cause of positive indirect antiglobulin tests (IAT) in pregnant women in the 2012 – 2017 period in northwestern Croatia and tested at the Croatian Institute for Transfusion Medicine. METHODS: Analyzing the results of immunohematological tests for pregnant women in the 2012 - 2017 period at the Croatian Institute for Transfusion Medicine. The tests were performed using the Twin Sampler Swing, Tango Optimo, Tango Infinity, Ih-1000 System. The immunohematological tests were performed using gel technology in microcrystals and the hemagglutination method in microtiter plates. RESULTS: The total number of pregnant women tested over a period of six years in northwestern Croatia was 43,740. The highest number of anti-D antibodies detected in the observed period was 240 (69.8%) of a total of 344 Rh immunizations. The total anti-D antibody in 43,740 pregnant women was 0.5%. Among the detected anti-D antibodies, 0.2% had active anti-D immunization and 0.4% had passive anti-D immunization in northwestern Croatia. CONCLUSION: The results justified the need for regular immunofluorescence testing during pregnancy and the possibility of introducing a more modern algorithm for pregnancy and childbearing.