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

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.