Background: Analysis of reticulated platelets (RP), the youngest form of platelets in peripheral blood, is useful for assessment of thrombopoietic response in thrombocytopenic conditions due to intense immunological platelet destruction. Aim: The aim of the study was to assess the value of RP measurement for differentiation between pregnancyrelated thrombocytopenia (PT), immunological thrombocytopenia (IM ) and hereditary thrombocytopenia (HT) in pregnant women with platelet count below 100 G/L. Material: The study included 49 pregnant thrombocytopenia women (21 with PT, 22 with IM , 6 with HR) as well as 22 healthy pregnant women (Control). Methods: The percentage of RP in peripheral blood was measured using double staining with: PE-labeled anti CD41 (Dako) and thiazole orange (Beckton Dickinson). The measurements were performed several times during pregnancy (II and III trimester) and delivery. Anti-platelet antibodies were tested by immunofluorescence and immunoensimatic assays. HPA1a antigen was determined by PCR/ SSP. Results: The average platelet count in all groups of thrombocytopenia women was significantly lower than in control group. The mean RP percentage in the control group (5.31%) was within the range of the haematological normal value (0.5-6%), and for thrombocytopenia women it was: 9.19% for PT women, 14.75% for IM women and 14.94% for HT women and was significantly higher than that in the control group. In the group of IM pregnant women the RP percentage was significantly higher in the II trimester than in the PT women. Anti-platelet antibody and HPA1a antigen testing excluded alloimmunological/fetus/neonatal thrombocytopenia in the study material. Conclusion: RP analysis has been proved useful for preliminary differentiation of PT and IT in the II trimester of pregnancy. Higher RP percentage informs the physician of the likelihood of immunological thrombocytopenia in the pregnant woman as well as of the delivery of a thrombocytopenia child.