Debate persists around the success rates of cleavage stage versus blastocyst transfers in fresh cycles. Freeze all and embryo pooling protocols have made vitrification and thaw cycles indispensable, introducing another angle to the decision for the best stage to cryopreserve embryos.
Aims: To compare the pregnancy rates of embryos vitrified and transferred post-thaw on day 5 (FOD5) against that of embryos vitrified on day 3 and transferred post-thaw after culture as day 4 morulas or day 5 blastocysts (FOD3).
Settings and Design: Retrospective study in a private clinic.
Methods and Material: A total of 163 freeze-thaw transfer cycles in two groups. One group involved 76 cycles whose embryos were vitrified on day 3 (FOD3) and transferred either after culture to day 4 morulas or day 5 blastocysts. Another group was of 86 cycles in which blastocysts were cryopreserved on day 5 (FOD5) and transferred after a 2-hour incubation period post-thaw.
Statistical analysis used: [i] Odds ratio of success for dichotomous outcomes [ii] the Chi-squared method.
Results: 37 of the 76 FOD3 cycles (48.68%) and 41 of the 86 FOD5 cycles (47.67%) had a positive outcome.
Conclusions: No statistical difference in pregnancy rates between embryos cryopreserved at cleavage stage on day 3 followed by a minimum of 1 day of culture post-thaw versus those cryopreserved and transferred at the blastocyst stage.