Bypassing the effect of zona pellucida changes on embryo formation following cryopreservation of bovine oocytes.

OBJECTIVE: To evaluate the effects of zona pellucida changes following the cryopreservation of bovine oocytes using two different techniques. DESIGN: Prospective randomised study. SETTING: University research facility and IVF research laboratory, NURTURE, University of Nottingham, UK. INTERVENTION: 508 bovine oocytes were collected from abattoir-derived ovaries and cryopreserved by slow freezing using standard straws and a new vitrification method using our self-constructed cryoloops. After thawing, the oocytes were inseminated by ICSI and standard IVF. MAIN OUTCOME MEASURES: Oocyte degeneration and oocyte cleavage. RESULTS: Cleavage rates after IVF in fresh oocytes was higher (49.5%) than the cryopreservation groups (slow freezing: 15.4% and vitrification: 25.8%), whereas after ICSI, the rates were similar (fresh: 17.3%, slow freezing: 9.4%, vitrification: 16.0%). CONCLUSIONS: Zona pellucida changes after oocyte cryopreservation significantly reduce the embryo formation rates after IVF. ICSI bypasses this complication and in selected species it could be an appropriate method of insemination.

New protocol for commencing the GnRH antagonist in assisted conception treatment cycles: elimination of the premature LH surge with similar pregnancy rates.

GnRH antagonists have been used with increasing frequency in assisted reproduction treatments over the past few years and have been associated with quicker and more profound LH suppression and shorter treatment cycles than conventional GnRH agonists. Usually, these are commenced on day 6 of FSH stimulation without allowing for patient variation in response to treatment. The study was aimed at individualising this protocol to the patients' ovarian response. The control group included 215 treatment cycles where the GnRH antagonist was commenced on day 6 of FSH stimulation. A new individualised protocol was formulated, applied to practice and 172 treatment cycles following that were analysed. The study group had no premature LH surges (LH > 10 iu x mL(-1)) compared to the control group who had a rate of 4.1%. There was also a higher fertilisation and clinical pregnancy rate in the study group (P = 0.06). It is concluded that the new individualised GnRH antagonist protocol eliminates premature LH surges in assisted conception treatment cycles and may improve clinical pregnancy rates compared to the conventional protocol of "day 6 commencement".

Cryopreservation of bovine oocytes: is cryoloop vitrification the future to preserving the female gamete?

The cryoloop is a technique where a thin nylon loop is used to suspend a film of cryoprotectant containing the oocytes and directly immersing them in liquid nitrogen. 508 bovine oocytes were collected, of these 351 were cryopreserved by slow freezing using standard straws or a new vitrification method using our self-constructed cryoloops and the remainder were controls. After thawing, the oocytes were inseminated by ICSI or standard IVF. The cryoloop vitrification method yielded a survival rate of 90.5% and the slow freezing technique a rate of 54.4% (p < 0.0001). When ICSI was performed, cryopreservation by the cryoloop vitrification method resulted in very similar cleavage rate to controls (16.0% vs. 17.3%) but slow freezing produced a slightly lower rate (9.4%). Cleavage rates after IVF in fresh oocytes was higher than the cryopreservation groups (49.5% vs. 15.4% and 25.8%), whereas after ICSI the rates were similar in all groups (17.3% vs. 9.4% and 16%). It is concluded that the new cryoloop vitrification technique followed by ICSI produce good embryo formation results and they could hold the future for effective oocyte cryopreservation.