Factors affecting the intracytoplasmic sperm cell injection outcomes: A meta-analysis of porcine studies

Intracytoplasmic sperm cell injection (ICSI) has the potential to produce gene-edited (GE) pigs for biomedical research, but its success is limited. The factors impeding ICSI in pigs are impractical in-vivo oocyte production, incomplete cytoplasmic maturation of in-vitro matured (IVM) oocytes, inefficient methods for sperm selection and membrane removal, abnormal sperm nucleus decondensation, substandard protocols for oocyte stimulation, suboptimal in-vitro culture (IVC) systems, and high embryonic/fetal losses.

The aim of this review is to investigate the effects of interventions in ICSI on oocyte activation, fertilization, cleavage, blastocyst, blastomere count, and live birth by means of robust statistical meta-analytical methods.

A total of 61 studies published between 1905 ∼ 2024 met the inclusion criteria. The results of the meta-analysis suggested that manipulation in the IVM media did not improve oocyte developmental competency to blastocysts but increased the blastomere count, especially with the addition of thiol compounds. Consistently, manipulation with sperm was beneficial only for increasing the cleavage and blastomere count. Exogenous stimulation increased the relative risk (RR) for oocyte activation (10 %), fertilization (33 %), cleavage (18 %), and blastocyst formation (71 %) but did not affect the blastomere count. Chemical stimulation either pre- or post-ICSI was more beneficial than electrical stimulation. Manipulation of the culture increased the RR for oocyte activation (14 %) and fertilization (37 %) but did not benefit cleavage, blastocyst formation, or blastomere count. The subgroup analyses revealed that supplementation with thiol compounds was indeed beneficial. Our network meta-analysis also supported the findings of classical meta-analyses showing that cysteine, cysteamine, epidermal growth factor, amino acid supplementation in maturation and culture media, and Triton treatment of sperm improved blastocyst formation. The overall success rate of live births from total embryos transferred after ICSI was not greater than 2 %. Although, manipulations that were beneficial for ICSI outcomes were identified in this meta-analysis, however, areas where more robust data are needed to reach a conclusive decision are highlighted.