Implantation potential and clinical impact of cryopreservation--a review.

The ability of human embryos to survive the freezing and thawing process is reflected in their implantation potential. Although cryopreservation appears to affect adversely the capacity of human embryos to implant, it has also been shown to enhance consistently IVF outcome. Moreover, despite the reduced implantation potential of cryopreserved embryos as compared to fresh embryos, multiple pregnancies are frequent in frozen embryo transfer (FRET) cycles. There is no conclusive evidence that the stage of development at the time of freezing provides a clear advantage for the outcome of a FRET cycle. On the other hand, a decreased chance for pregnancy achievement appears to exist with advanced maternal age. Neither the mode of endometrium preparation nor the length of cryostorage appears to affect the outcome of FRET cycles which is positively associated to the achievement of pregnancy in the corresponding fresh cycle. Available evidence suggests that there are no adverse consequences in the babies born after embryo cryopreservation, although larger studies are necessary to allow solid conclusions.