Survival of human oocytes cryopreserved with or without the cumulus in 1,2-propanediol

Although cryopreservation of human preembryos has been carried out with success, the cryostorage of oocytes, which pose fewer controversial moral, ethical, and legal problems has been much less successful. Various attempts to cryopreserve human oocytes have been mostly unsuccessful and the search for an optimal protocol for oocyte cryopreservation remains elusive. We therefore undertook this study to determine the effect of oocyte cryostorage in 1,2-propanediol.

Mature human oocytes with or without their cumuli were cryopreserved in precooled 1,2-propanediol, then thawed and inseminated with sperms for in vitro fertilization. The outcome of insemination and subsequent embryonic development were also recorded and compared.

Postthaw cryosurvival rate was significantly better when cryostorage was carried out with the oocyte cumulus intact as compared to those oocytes denuded of their cumuli (54 versus 27%, respectively; P < 0.05). Eight (44%) of 18 surviving postthaw oocytes with intact cumuli were fertilized normally, with cleavage in six, as compared to two (25%) and one, respectively, of those denuded of their cumulus prior to cryostorage. Development to the blastocyst stage was achieved in three embryos derived from oocytes with an intact cumulus at cryostorage.

We conclude that 1,2-propanediol can be used with success in oocyte cryopreservation, although the issue of parthenogenecity is still to be resolved. Oocyte's with intact cumulus survive cryostorage better than those without it.