Ultrarapid Freezing (Vitrification) of Human Embryos : A Preliminary Report

Abstract

Objective to report a simple and economical ultrarapid freezing technique, the so-called vitrification technique, on cryopreservation of cleavage stage human embryos, and to report the first successful pregnancy resulted from this promising technique.

Subjects Eleven infertile patients with 44 surplus embryos of 2- to 8-cell stage. All embryos were cryopreserved using the vitrification protocol which has been tested previously. The medium was consisted of 5.6 M dimethyl-sulphoxide (DMSO), 0.25 M sucrose and 20% fetal calf serum in phosphate-buffered saline. Two to three minute equilibration of the embryos with the cryoprotectant was carried out at 4 C. After ultrarapid freezing and thawing, the embryos were morphologically evaluated and selectively transferred into a natural ovulatory cycle with the average number of 2.4 embryos per patient.

Main outcome measures Cryosurvival rates and pregnancy outcome.

Results Seventy percent (31/44) of the frozen-thawed embryos did not degenerate. More than eighty percent (26/31) of these survived embryos with at least 50% intact blasto meres were transferred to 11 patients. Two patients became pregnant, one biochemically and another gave birth to a healthy fullterm baby in January 1995.

Conclusion This is the first series showing that cryopreservation of human embryos by vitrification technique resulted in a successful pregnancy. This simple and easy-to-do ultrarapid freezing technique seems to be more practical than the conventional slow freezing protocol.