Are Vitrified Warmed Blastocysts Stage Embryos (Day 5-6) Effective as Vitrified Warmed Cleavage Stage Embryos (Day 2-3) in Terms of Clinical Pregnancy?

Introduction:
Blastocyst stage embryo transfers (BSE) results in higher implantation and clinical pregnancy rates (CPR) than transfers in cleavage stage embryo (CSE). The optimized embryo stage for transfer in vitrified warm (VW) cycles is inconsistent.

Aim:
To compare CPR of vitrified warm blastocyst transfers (day 5-6) with cleavage stage embryo transfers (day 2 to 3).

Methods and Materials:
The study included vitrified good quality days 2-3 embryos (4-8 cells,gradeI,II) and days 5-6 blastocysts (grades 4AA-3BB).The blastocysts originated from "blastocyst only" cycles as well as from cycles in which poor quality embryos were left over to develop to the blastocyst stage, since they were not good enough for transfer or freezing on days day 2-3. All were vitrified in an open system using Sage and Origio vitrification media, with open device. Warmed CSE and BSE were replaced in natural and caped medicated cycles on days 3/5. We included only CPR and excluded patients aged over 41.

Results:
CPR of WV blastocysts is significantly higher than for CSE, (46/115) 40% vs (172/587) 29.3% (p<0.05). The number of transferred CSE and BSE were similar (1.7±0.64 and 1.6±0.59 respectively). The CPR of day 5 BSE from "blastocysts only" cycles was significantly higher than for CSE 51.4% (18/35) vs 29.3% (p<0.05). In this group, there is a tendency towards younger patients (30±4.89 vs 32.6±5.67). Day 6 VW blastocysts CPR (15/53) 28.3% was similar to the CPR for VW days 2-3 embryos (29.3%).

Conclusions:
We obtained better CPR for good quality VW day 5 blastocysts as compared to good quality CSE.