Hyaluronic acid (HA) is a major component of the cumulus complex surrounding oocytes. Intracytoplasmic sperm injection (ICSI) involves injection of a selected sperm into the oocyte. Embryologists select sperm with normal morphology and progressive motility. Physiologic intracytoplasmic sperm injection (PICSI) involves sperm selection for ICSI based on hyaluronan binding. Mature sperm which bind to HA have greater genomic integrity and reduced levels of DNA fragmentation. Earlier observational studies demonstrated improved outcomes in assisted reproductive technologies (ART) including improved clinical pregnancy rates, decreased miscarriage rates and higher live birth rates. A large multicentre randomized trial, the HABSelect trial, which included over 2,500 couples, found that PICSI did not improve term (\>37 weeks gestation) live birth rates compared to standard ICSI. However, mechanistic analysis of the data from the HABSelect trial showed a significant reduction in miscarriage rates, most notable in couples where the woman was aged over 37 years where a significant reduction in miscarriage rate was seen (40% with ICSI vs 15% with PICSI). A 2021 retrospective sibling oocyte study, including 45 cycles, compared fertilisation and embryo development and found higher fertilisation rate in PICSI cycles. No difference was observed in clinical pregnancy rates; miscarriage rates and live birth rates were not reported. We aim to prospectively study PICSI vs standard ICSI in sibling oocytes to investigate if PICSI improves embryological and ART outcomes, particularly fertilisation rate, embryo euploid status and miscarriage rate, where the female patient is aged over 35 years.