M.J. De los Santos

Effect of different cryopreservation protocols on the metaphase II spindle in human oocytes

The aim of this study was to evaluate the impact of different cryopreservation protocols on the repolymerization of metaphase (M)II spindles in human oocytes. Fresh aspirated donor oocytes were cryopreserved 3-4 h after retrieval using four different protocols: slow freezing using 1.5 mol/l 1,2-propanediol (PROH) + 0.2 mol/l sucrose (n = 36); 1.5 mol/l PROH + 0.3 mol/l sucrose (n = 34); 1.5 mol/l PROH + 0.3 mol/l sucrose with Na(+) depleted-choline replaced media (n = 27), and vitrification by the Cryotip method (n = 23). The control group comprised 34 fresh oocytes. Three hours after thawing, surviving and control oocytes were fixed for meiotic spindle/chromatin assessment. Survival rates were 63.8, 73.5, 74.1 and 86.9% respectively for the four protocols described above. Survival for vitrified oocytes was higher than that observed for slow freezing with 0.2 and 0.3 mol/l sucrose (P < 0.05). The proportion of oocytes showing normal spindle configuration was similar for the four protocols (81, 73.9, 88.9 and 81.3% respectively) and 88.5% for controls, showing that the MII spindle returns to its normal configuration after 3 h of post-thawing incubation under standard conditions, irrespective of the cryopreservation technique used.

Oxygen consumption is a quality marker for human oocyte competence conditioned by ovarian stimulation regimens

OBJECTIVE To evaluate the effect of different ovarian stimulation protocols on oocyte respiration and to investigate the relationship between oocyte oxygen consumption and reproductive outcome. DESIGN Prospective observational cohort study. SETTING Infertility clinic in a university hospital. PATIENT(S) A total of 349 oocytes from 56 IVF treatment cycles in our oocyte donation program. INTERVENTION(S) None. MAIN OUTCOME MEASURE(S) Average oocyte oxygen consumption rate in fmol/s. We correlated oxygen consumption values with ovarian stimulation features, fertilization, embryo quality on days 2 and 3, and implantation. RESULT(S) Differences in the measured oxygen consumption rates were found depending on which type of gonadotropins were used in the stimulation protocol. Higher consumption rates were found for oocytes that underwent normal fertilization compared with rates from nonfertilized or abnormal oocytes (odds ratio = 1.340; 95% confidence intervals = 1.037-1.732). Furthermore, higher oxygen consumption was observed for those oocytes which generated embryos that implanted compared with those that did not implant (6.21 ± 0.849 fmol/s vs. 5.23 ± 0.345 fmol/s. CONCLUSION(S) Measurement of oxygen consumption rates for individual oocytes before fertilization provides a noninvasive marker of oocyte quality and hence a quantitative assessment of the reproductive potential for the oocyte.