The value of fast blastocoele re-expansion in the selection of a viable thawed blastocyst for transfer.

OBJECTIVE: To investigate the role of fast blastocoele re-expansion in the selection of viable thawed blastocysts for transfer.

DESIGN: Retrospective study.

SETTING: Academic assisted reproductive program.

PATIENT(S): Transfer cycles were divided into two groups according to the presence or absence of fast re-expanded blastocysts. In group I (124 cycles), all transferred blastocysts had fast re-expanding blastocoele. In group II (113 cycles), no fast re-expanded blastocysts were included in the transfer.

INTERVENTION(S): Blastocyst survival was defined as >50% of cells remaining intact after thaw and re-expansion after culture in vitro for 2-4 hours before transfer. Blastocysts with >or=50% re-expansion were designated as fast re-expanded blastocysts.

MAIN OUTCOME MEASURE(S): Percentage of blastomere loss immediately after thaw, degree of blastocoele re-expansion, and clinical outcomes (pregnancy and implantation rates).

RESULT(S): The rates of survival and fast blastocoele re-expansion of partially intact blastocysts were significantly reduced as compared with fully intact blastocysts. Significantly higher rates of clinical pregnancy (37.1% vs. 16.8%) and implantation (26.7% vs. 11.3%) were obtained when all transferred blastocysts had fast re-expanding blastocoele as compared with those transfers without fast re-expanded blastocysts included.

CONCLUSION(S): Our results showed that blastomere loss of thawed blastocyst was associated with a reduced ability to re-expand. As a discriminative morphologic marker of superior embryo viability, a fast re-expanded blastocyst would be given priority for transfer to better utilize the cryopreserved blastocysts.