Slow controlled-rate freezing of sequentially cultured human blastocysts: an evaluation of two freezing strategies.

BACKGROUND: To optimize blastocyst cryopreservation, the prerequisite is to develop a better understanding of factors that influence their survival and implantation potential. Therefore, the aim of the present work was to evaluate, retrospectively, the outcome of blastocyst cryopreservation in a day 2/3 fresh embryo transfer programme. METHODS: Two different freezing strategies were compared: a first strategy (strategy A: 3007 blastocysts frozen) consisted of freezing those blastocysts that had at least a cavity; a second strategy (strategy B: 3831 blastocysts frozen) consisted of freezing only more advanced stage blastocysts with a good quality inner cell mass and trophectoderm. The outcome of cryopreservation, as related to the two different freezing strategies, was analysed. In addition, after freezing and thawing, we evaluated the influence of blastocyst developmental characteristics on immediate morphological survival and further development in vitro. RESULTS: The immediate morphological survival after thawing was higher for early blastocysts as compared to advanced and hatching blastocysts. The further developmental potential in vitro of thawed blastocysts was higher for advanced and hatching blastocysts as compared to early blastocysts. As a result, the percentage of deliveries, calculated as a percentage of started thawing cycle, and the percentage of children born, calculated as a percentage of embryos transferred, was not different for strategies A and B. CONCLUSION: The results clearly indicate that culture conditions and cryopreservation procedures of blastocysts need to be further improved.

Outcome for donors and recipients in two egg-sharing policies.

OBJECTIVE: To assess the effect of two different donation policies on results of egg-sharing. DESIGN: Retrospective analysis. SETTING: Tertiary referral center. PATIENT(S): One hundred five donor-recipient pairs participating in an egg-sharing program between 1998 and 2001. INTERVENTION(S): Egg-sharing was performed according to policy A (retrieval of at least 12 oocytes, with more oocytes allocated to the donor) or policy B (retrieval of at least 8 oocytes, with equal distribution of oocytes between donors and recipients). MAIN OUTCOME MEASURE(S): Delivery rate and cycle cancellation rate. RESULT(S): Policy B resulted in a decreased cycle cancellation rate in the recipient group compared with policy A (9.7% vs. 29.7%, respectively; P