EMBRYO CRYOPRESERVATION

CRYOPRESERVATION STRATEGY

Cornell program developed the following strategy to determine when and how to freeze various embryos:

1) Never freeze only one embryo, unless the patient has other embryos previously cryopreserved and stored. Twelve years of experience indicate that the results of transferring only one embryo after freezing and thawing are too poor to justify the cost for the patient and the overwork for the laboratory crew (clinic pregnancy rate 14% per transference). Try to freeze at least three embryos if possible. After thawing, best results happen when a patient transfers more than two embryos (clinic pregnancy rate 50% per transference).

2) Keep in culture all pre-embryos judged non acceptable for tranference and freezing (more than 20% fragmentation, < 6 cells on day three) for three days. Document every day observations about number of cells and morphology. Freeze any developing blastocyst on days 5 and 6, if two or more seem healthy (not frequent).

Pacients over 40

1) If the patient’s previous history presents pre-embryos with good morphology, then keep 5 to 7 of them in culture (depending on the exact age)and freeze the rest in pronuclear stage. Plan to freeze the remainder on day three if morphology is good.

2) If the patient’s history shows poor pre-embryo morphology, or if there is no previous history to be evaluated, then keep 7 to 10 embryos in culture and freeze the remainderin pronuclear stage. Plan to freeze additional pre-embryos on day 2 or three if two or more exhibit less than 20% fragmentation and normal cleavage.

3) If the patient’s previous history indicates poor morphology or slow embrionary development, so wait until day 3 before considering freezing.

Patients under 40

1) Do not freeze pre-embryos at the pronuclear stage unles there are more than 10 pre-zygote available and the previous history presents good morphology embryos.

2) Freeze after cleavage, only if two or more embryos possess excellent morphology and regular cleavage, that is available above the number of embryos required for transference.

3) Consider tranferring 5 fresh embryos in patients aged 41 to 43, and 6 embryos over 43 (with both patient and medical consent).

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