This document summarizes the results of a clinical audit comparing outcomes of 706 embryos that were either vitrified or slow-frozen for fertility treatment. The audit found statistically significant improvements in survival rate, pregnancy rate per embryo thawed, clinical pregnancy rate per embryo thawed, and implantation rate per embryo thawed for embryos that were vitrified compared to those that were slow-frozen after adjusting for patient age differences between the groups. The conclusion is that vitrification led to highly significant improvements in all outcome measures compared to slow-freezing based on this retrospective analysis of data.

1. VITRIFIED VS. SLOW-FROZEN
BLASTOCYSTS: A CLINICAL AUDIT
FOR 706 EMBRYOS
Cawood, S., Doshi, A.
and Gotts, S.
The Centre for Reproductive and
Genetic Health, London, UK.

2. Aim
To retrospectively analyse and compare SR,
PR, CPR and IR between FTET patients
whose embryos were slow frozen versus
those patients whose embryos were vitrified.
Results to be calculated per embryo thawed

3. Method – Raw Data
Inclusion Criteria: All FTET cycles
where a blastocyst (day 5/6) was
thawed/warmed between the period
01.01.2006 – 31.11.2009.

4. Method – Media and Protocols
Slow frozen embryos were frozen using G-
FreezeKit Blast™ and thawed with G-
ThawKit Blast™ (glycerol + sucrose)
according to the Vitrolife protocols.
Blastocysts were vitrified using COOK
(Sydney IVF) media; Blastocyst Freezing Kit
and warmed using Blastocyst Thawing Kit
(DMSO, ethylene glycol and trehalose).

5. Method – Statistical Analysis
A chi-squared test (with continuity correction)
was used to compare the two proportions
and two-sample t-tests to compare patient
populations.
Logistic regression was then performed to
compare end points.
Multiple regression was used (after adjusting
for age) to calculate rates ‘per embryo
thawed’ for each patient.

6. Results
No statistical difference between:
> day of freeze (d5/6)
A difference was found in the patient’s age
Mean Age: 35.2 SD 4.45 (vitrified-warmed)
Mean Age: 36.4 SD 4.24 (slow-thawed)

7. Results and significance values
after adjusting for age
VITRIFIED-WARMED SLOW FROZEN-
THAWED
NO. OF EMBRYOS 347 359
THAWED
SURVIVAL RATE 317/347 (91.4%) 274/359 (76.3%)
p = 0.001
P.R. PER EMBRYO 94/347 (27.1%) 71/359 (19.8%)
THAWED p = 0.01
C.P.R. PER EMBRYO 80/347 (23.1%) 56/359 (15.6%)
THAWED p = 0.003
I.R. PER EMBRYO 106/347 (30.5%) 68/359 (18.9%)
THAWED p = 0.001

8. Conclusion
A retrospective audit of CRGH data
Highly significant improvement in all outcome
measures when embryos were vitrified
Cryopreservation programmes of utmost
importance in era of eSET (cumulative
pregnancy rates)
Prospective randomised trials, long term data
needed.

9. Thank You