Assessment of the calcium releasing machinery in oocytes that failed to fertilize after conventional ICSI and assisted oocyte activation.

Research Question: Can oocyte-related activation deficiencies be evaluated in oocytes that failed to fertilize after intracytoplasmic sperm injection (ICSI) combined with assisted oocyte activation (AOA)?

Design: Evaluation of the spindle-chromosome complexes and intracellular distribution of inositol trisphosphate type 1 receptors (IP3R1) in in-vitro matured (IVM) and failed-to-fertilize oocytes from patients undergoing AOA. Assessment of the oocyte-related Ca releasing capacity in response to Ca ionophores and sperm microinjection in oocytes that failed to fertilize after ICSI or ICSI-AOA.

Results: IVM oocytes from patients undergoing conventional ICSI (control) and ICSI-AOA (study group) revealed a similar normalcy of spindle-chromosome complexes and distribution patterns of IP3R1. Failed-to-fertilize oocytes from both groups showed significant differences in proportion of normal or abnormal spindle-chromosome complex conformations. However, migration of IP3R1 was identified in a higher proportion of failed-to-fertilize oocytes after ICSI-AOA than after conventional ICSI. It was further observed that oocytes which failed to fertilize, either after ICSI or ICSI-AOA, mostly retain their capacity to respond to stimuli such as exposure to Ca ionophores or to sperm microinjection.

Conclusions: Evaluation of spindle-chromosome normalcy and distribution of IP3R1 does not help identify the presence of Ca releasing deficiencies in these oocytes. However, oocyte Ca analysis adds value in identifying Ca releasing incapacity of oocytes that failed to fertilize after ICSI or ICSI-AOA. Some patients experiencing fertilization failure after ICSI-AOA present with a suspected activation deficiency downstream of the Ca machinery, which cannot be overcome by ICSI-AOA based on the use of Ca ionophores.