Objective: to compare survival, clinical pregnancy and ongoing pregnancy rates of blastocysts vitrified on day 5 and those which had one day delay and vitrified on day 6.
Materials & Methods: This was a retrospective study in a University based and a private
practice setting. The study included 210 vitrified warmed cycles, 135 patients underwent
vitrifivation at day 5 (group I) and 75 patients at day 6 (group II). The main outcome
measures were blastocyst survival and clinical pregnancy/embryo transfer were primary
outcomes. Ongoing pregnancy/embryo transfer was the secondary outcome.
Results: Blastocyst post-warming survival rates were comparable between both groups
(92.9% (263/283) of day 5 versus 94.9% (166/175) of day 6 blastocysts). There was no
statistically significant difference between the 2 groups regarding the mean number of
transferred blastocysts. Clinical pregnancy rates were 40.6% (52/128) & 43.7% (31/71)
in women who undergone vitrification at day 5and day 6 respectively with no significant
differences. Similarly, ongoing pregnancy rate was comparable between the 2 groups,
37.5% (48/128) versus 39.4% (28/71) in groups I & II.
Conclusion(s): blastocysts vitrified on day 5 have the same survival, clinical and ongoing
pregnancy rates of blastocysts which had one day delay and vitrified on day 6