Nearly 400,000 embryos are stored in the United States, the majority of which (88.2%) are targeted for patient use. Few are available for research (2.8%), limiting possible conversion into embryonic stem cell lines.
The incidence of cell injury, embryo survival, and implantation following cryopreservation of zygotes and two- to five-cell embryos was studied in 100 patients in order to evaluate the effect of duration of storage. The incidence of individual cell survival was 58% regardless of the length of time kept in liquid nitrogen or the stage of the embryo at freezing. There were 104 of 208 (50%) thawed embryos that survived completely intact, and of those, 24 implanted successfully. Twenty-one (21%) patients had a clinical pregnancy; two of them miscarried Neither the survival of zygotes or cleaved embryos upon thawing nor the incidence of implantation was affected by the duration of cryostorage.
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