Etiology. 1. Utero-placental ischaemia: Abnormal development of the placental bed vessels /shallow trophoblast invision in spiral arteries /acute arterosis 2. Endothelial cell activation/dysfunction. Cytotoxic factors: oxygen free raicals /lipid peroxidation /very low density lipoprotein(vlDL)/fibronection / platelet derived growth factor( PDGF)/tumor necrosis factor-a(TNF-a)/interleukins-6(IL-6) anti-vascular endothelial factor / endothelial inhibitive factor 3. Immunity i (1) fail to express HLA-G mRNA or protein (2)abnormal maternal immune situation such as Ts/Th decrease and ThI function dominent 4. Genetics gene recessive traitEtiology : 1. Utero-placental ischaemia : Abnormal development of the placental bed vessels / shallow trophoblast invision in spiral arteries / acute arterosis / 2. Endothelial cell activation/dysfunction: Cytotoxic factors : oxygen free raicals /lipid peroxidation / very low density lipoprotein(VLDL) /fibronection / platelet derived growth factor( PDGF) / tumor necrosis factor-a (TNF-a) /interleukins-6 (IL-6) / anti-vascular endothelial factor /endothelial inhibitive factor 3. Immunity ; (1) fail to express HLA-G mRNA or protein . (2) abnormal maternal immune situation such as Ts/Th decrease and Th1 function dominent . 4. Genetics : gene recessive trait