Assisted oocyte activation re-envisioned: a more physiological approach

To determine the gamete-specific etiology of severe or total fertilization failure after intracytoplasmic sperm injection (ICSI) and to evaluate the efficacy of individualized assisted oocyte activation (AOA) strategies guided by sperm phospholipase C-zeta (PLCζ) content.

A pilot topographic analysis on PLCζ content in ejaculated, epididymal, and testicular spermatozoa was performed to better understand the fertilization capability of spermatozoa at different maturational stages. The prospective case series included 135 couples with complete or severe fertilization failure following ICSI, who were screened for PLCζ content and allocated as having oocyte- or sperm-related deficiency based on PLCζ assay results. According to gamete-specific deficits, cycles were treated with AOA, that is, ionophore-only, rhPLCζ-only, or combined treatment. Embryological and clinical outcomes of AOA cycles were compared with those of historical non-AOA ICSI cycles.

PLCζ content varied according to the maturity and origin of spermatozoa in the pilot study. Compared with historical cycles, AOA using ionophore and rhPLCζ each rescued fertilization and improved pregnancy outcomes with comparable efficiency. Notably, dual AOA (ionophore + rhPLCζ) yielded the greatest improvements in fertilization (24.1% vs. 73.2%, P < 0.0001), implantation (6.5% vs. 31.7%, P < 0.01), and ongoing pregnancy rates (0% vs. 63.3%, P < 0.0001), even in cycles using testicular spermatozoa.

The introduction of recombinant PLCζ enabled specific correction of gamete-specific fertilization failure. Dual AOA (ionophore + rhPLCζ) was particularly effective in cases of compounded etiology and with immature spermatozoa, supporting a shift from empiric to individualized AOA strategies.