Type of publication:
*Hatton A.; *Gittins V.; *Binnersley S.; *Hughes G.; *Lavender A.; *Kasraie J.
Human Fertility; 2013; vol. 16 (no. 3)
Introduction : Blastocyst culture is now routine, but national practice is not uniform. Extended culture to day 6 (D6) may be considered controversial due to possible associated epigenetic factors and a perceived decrease in viability of D6 blastocysts. Conversely, cryopreservation on D6 may reduce the number of fresh egg collections required, minimising risk to patients and cost to the healthcare economy, but do the benefits outweigh the potential risks? Method : National survey of practice, protocol and outcome. Results: 40 clinics responded 7.5% did not culture to blastocyst. 92.5% cultured to blastocyst in 5-80% of treatment cycles. 59.5% cultured to D6 if blastocysts were unavailable for transfer on day 5(D5) and between 0 and <= 90% of patients had fresh D6 transfers. Average clinical pregnancy rates (CPRs) for fresh D5 vs D6 transfers were 44.3% vs 25.7%. All clinics culturing to blastocyst cryopreserved. 89% cultured to D6 if no cryopreservation occurred on D5. 83.5% cultured remaining embryos to D6 whether or not cryopreservation occurred on D5. Average CPRs for cryopreserved D5 vs D6 blastocysts were 31% vs 28.3%. 89% believed culturing to D6 was worthwhile. Other data (e.g. culture system, cryopreservation method, carrier, media) were also collected and analysed. Conclusions : The majority of respondents cultured to, and cryopreserved, on D6. CPRs varied greatly between centres but were generally lower in fresh D6 vs D5 transfers. Nevertheless, results suggest that D6 transfer is worthwhile for patients without D5 blastocysts. Additionally, CPRs for cryopreserved D6 blastocysts were very similar to D5 and appeared slightly higher than fresh D6. Whilst it remains to be seen whether cryopreserved D6 blastocysts are more viable than fresh, it certainly appears that cryopreservation of D6 blastocysts is effective and beneficial to both patients and the healthcare economy by reducing risks from stimulation/ egg collections and overall costs whilst maximising cumulative success.