BACKGROUND: Recurrent spontaneous abortion, a common condition in reproductive medicine, often arises from complex factors and lacks specific treatments. While studies have associated folate metabolism abnormalities with poor embryonic development, research on methionine metabolism, particularly homocysteine levels, has been limited. METHODS: In this study, we analyzed blood samples from women with RSA and those with normal pregnancies. RESULTS: We observed elevated homocysteine levels in women with RSA, which were correlated with increased total plasma microparticles, endothelial microparticles (EMPs), and free plasma DNA. Furthermore, we exposed human umbilical vein endothelial cells (HUVECs) to varying concentrations of homocysteine (0, 0.5, 1, 2, 4, 8 mmol/L). We found that higher homocysteine levels exacerbated its cytotoxic effects on HUVECs. Flow cytometry revealed that homocysteine compromised cell membrane integrity, enhanced membrane permeability, and promoted EMPs release. Our findings suggest that elevated homocysteine levels in women with RSA may induce significant endothelial cell apoptosis, leading to endothelial dysfunction and an increase in released microparticles and free DNA, potentially contributing to miscarriages. CONCLUSION: This study may contribute to understanding and exploring the underlying mechanisms of unexplained recurrent spontaneous abortion (URSA).