Prognostic factors for the success rate of embryo freezing.
To find some prognostic factors for the outcome of frozen-thawed cycles, we have retrospectively analysed all frozen pre-embryos that were thawed during 1993 and 1994 at two in-vitro fertilization (IVF) units in Sweden. Supernumerary pre-embryos were frozen from 551 oocyte retrievals and these resulted in 660 frozen-thawed cycles which lead to 623 thawed embryo transfers. The outcome of these transfers was 137 clinical pregnancies with a pregnancy rate of 22% per frozen-thawed embryo transfers. Women <40 years of age had a higher birth rate than those > or =40 years, 19 and 5% respectively (P < 0.01). Transfers with two and three pre-embryos resulted in pregnancy rates of 23 and 27%, respectively, compared with 14% for transfer of one embryo. A pregnancy resulting from the initial embryo transfers had a predictive value for results of the subsequent frozen-thawed cycle. Embryo grade and cleavage stage at the time of freezing was important for the survival of the frozen-thawed pre-embryos. The pregnancy rate was not influenced by the cleavage stage, but a tendency toward a lower pregnancy rate was seen for the embryos with lower grading. To conclude, cryopreservation seems to be beneficial in women <40 years of age, who have supernumerary pre-embryos of good quality for freezing and of which at least two can be transferred.
Karlström
P O
PO
Carl von Linné Kliniken, Uppsala, Sweden.
Bergh
T
T
Forsberg
A S
AS
Sandkvist
U
U
Wikland
M
M
D000328:Adult; D002970:Cleavage Stage, Ovum / Q000166:cytology; D015925:Cryopreservation; D004624:Embryo Transfer; D004622:Embryo, Mammalian / Q000166:cytology; D005260:Female; D005307:Fertilization in Vitro; D005615:Freezing; D006801:Humans; D011247:Pregnancy; D012099:Reproductive Techniques; D012189:Retrospective Studies; D013548:Sweden