Characterization of the injection funnel during intracytoplasmic sperm injection reflects cytoplasmic maturity of the oocyte

Abstract

Objective: To quantify cytoplasmic maturity on the basis of intracytoplasmic sperm injection (ICSI) injection funnel manifestation and to evaluate influence factors of the latter.

Design: Prospective study.

Setting: Private fertility center.

Patient(s): A total of 31 patients with good ovarian response.

Intervention(s): Mature and immature oocytes were injected intracytoplasmatically. Formation and persistence of an injection funnel was documented and measured.

Main outcome measure(s): ICSI funnel size, persistence of injection funnel, rates of degeneration and fertilization, embryo quality.

Result(s): Funnel volume in germinal vesicle stage oocytes (prophase I [PI]) was significantly smaller than that of metaphase I (MI) and MII oocytes. Immature eggs (PI, MI) almost never showed a persistent funnel 2-4 minutes after ICSI, whereas in MII eggs the funnel was still observable in 35% (117/334) of the cases. Uni- and multivariate analysis revealed that pipette type and stimulation protocol significantly influenced appearance of injection funnel. Funnel volume in oocytes that fertilized regularly was significantly higher compared with three-polar body and degenerated oocytes.

Conclusion(s): Oocyte maturation within the follicle is closely associated with a remarkable change in cytoplasm viscosity from an aqueous to a more viscous subtype. Precise evaluation of the injection funnel may help to explain deviations from expected ICSI outcome and could also assist in optimizing controlled ovarian hyperstimulation.

Keywords: ICSI; ICSI pipette; Injection funnel; controlled ovarian hyperstimulation; cytoplasmic maturity.