AbstractWe investigated the influence of DNA fragmentation index (DFI) onin vitrofertilization (IVF), embryo transfer (ET), and intracytoplasmic sperm injection (ICSI). We analyzed the semen parameters of 61 cycles in infertile couples undergoing IVF-ET and ICSI and determined DFI by sperm chromatin dispersion testing. Based on DFI, the patients were differentiated into a control group (DFI < 25%,n= 35) and a test group (DFI ≥ 25%,n= 26). Flow cytometry and immunofluorescence were used to investigate the extent of sperm reactive oxygen species (ROS) and apoptosis. We also investigated the effect of DFI on pregnancy outcomes of IVF-ET/ICSI. DFI was negatively related to sperm motility and positively correlated with ROS and apoptosis (P< 0.05). Abnormally elevated DFI reduced the rate of transplantable, high-quality embryos, implantation, clinical pregnancy, delivery, and live birth after IVF-ET, and increased the chance of early abortion per transfer cycle (P< 0.05). However, there was no significant correlation between DFI and fertilization rate, cleavage rate, transplantable rate, high-quality embryo rate, implantation rate, clinical pregnancy rate, early abortion rate, delivery rate and live birth rate when assisted by ICSI (P> 0.05). Sperm DNA integrity is crucial for fertilization and the development of healthy offspring. ROS may increase the level of DFI by inducing apoptosis in sperm.