Prognostic factors for the success rate of embryo freezing

• Published in: Human reproduction (Oxford) 1997-06, Vol.12 (6), p.1263-1266
• Main Authors: Karlström, P O, Bergh, T, Forsberg, A S, Sandkvist, U, Wikland, M
• Format: Article
• Language: English
• Subjects: Adult; Biological and medical sciences; Birth control; Cleavage Stage, Ovum - cytology; Cryopreservation; Embryo Transfer; Embryo, Mammalian - cytology; Female; Fertilization in Vitro; Freezing; Gynecology. Andrology. Obstetrics; Humans; Medical sciences; Pregnancy; Reproductive Techniques; Retrospective Studies; Sterility. Assisted procreation; Sweden
• ISSN: 0268-1161; 1460-2350
• DOI: 10.1093/humrep/12.6.1263

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 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