The aim of this study was to evaluate the immunohistochemistry and ultrastructural of syncytiotrophoblast and Hoffbauer cells in placental villi of HELLP syndrome patients. Placental samples with twenty control (normotensive) and twenty HELLP syndrome were fixed in 10% neutral formalin solution for paraffin-embedding wax protocol. Placental samples were fixed in 2.5% buffered glutaraldehyde and then, in 1% osmium tetra oxide for routine electron microscopic procedure. When the HELLP group fetal placental sections were examined, intracytoplasmic edema in syncytiotrophoblast, degenerative vacuoles and degenerative findings on cell surface membranes were observed. Moreover, villous edema was remarkable. The number of CD68 positive Hoffbauer cells per villus control group sections was 0.23 ± 0.02 and the number of CD68 positive cells per villus in HELLP group placenta sections was 0.83 ± 0.12 . The increase in the number of Hoffbauer cells per villus in the HELLP group was statistically significant (p

Development of the placenta without any complication is essential for normal pregnancy.The placenta is a multifunctional organ that plays a vital role in fetal development. Hofbauer cells are one of the most important groups of placental cells. These cells are placental macrophages and have a role in many placental events. The aim of this study is to investigate the placental distribution and density of Hofbauer cells and to contribute to the understanding of the causes and pathogenesis of complicated pregnancies. In this study, 60 full-term placentas were divided into 4 equal groups: control, preeclampsia, gestational diabetes (GDM), and ( hemolysis, elevated liver enzymes, low platelet) HELLP group. The placenta was dissected and the samples were fixed 10% neutral buffered formalin. Following routine paraffin wax procedure, 5 µm sections were stained with CD68 for marking Hofbauer cells. In immunohistochemical evaluation, Hofbauer cells in villous stroma showed positive CD68 expression. Immunostaining Findings: CD68 showed a granular staining pattern in the cytoplasm of Hofbauer cells. The group with the highest CD68 positive cell number was HELLP group and the number of cells per cell (1.46 ± 0.25) was significantly different from all groups. CD68 positive cell count in the placental villus was the highest in HELLP group and the number of Hofbauer cells per villus was significantly different from the other groups.