Developmental competence of oocytes showing increased cytoplasmic viscosity

The objective of the study was to investigate the developmental fate of oocytes with increased cytoplasmic viscosity as assessed by the persistence of the injection funnel after withdrawal of the ICSI pipette.

For this purpose, 1008 oocytes showing a characteristic injection funnel during ICSI were subdivided into two groups according to the oocyte's ability to restore its spherical shape within 2-3 min after ICSI. Fertilization and further development was evaluated in both groups. In addition, implantation and pregnancy rates were analysed.

In the funnel positive cohort (group 1) significantly fewer oocytes degenerated after injection (P < 0.01) compared with oocytes without persistent funnel (group 2). However, at zygote stage, presence of a halo (P < 0.05) and a optimal pronuclear pattern 0 (P < 0.01) was increased in group 2. In addition, significantly fewer poor quality embryos were found in this group (P < 0.01). The number of good quality blastocysts but not blastocyst formation was increased in group 2 (P < 0.05). This resulted in an increased clinical pregnancy rate if embryos which derived exclusively from funnel negative oocytes were transferred (P < 0.05).

Our data suggest that cytoplasm of higher viscosity delays development up to cleavage stage and impairs optimal development. Injection funnel persistence was found to be a negative prognostic marker of preimplantation development.