Human pregnancy following cryopreservation, thawing and transfer of an eight-cell embryo.

The widespread use of clomiphene citrate and exogenous gonadotrophins for in vitro fertilization (IVF) in human frequently results in the production of multiple embryos. Replacement of more than two embryos increases pregnancy rate but may result in multiple pregnancies with increased pre- and post-natal abnormality. Preservation of embryos for a limited time allows fewer embryos to be replaced on several different occasions and thus the problems of multiple pregnancy can be minimized, the effectiveness of a single IVF procedure increased and embryo replacement in adverse maternal conditions avoided. Preimplantation embryos have been successfully cryopreserved in many animal species. The sensitivity of embryos to cooling and freezing varies between species and stages of embryo development. We report here the cryopreservation procedures that allow a high survival rate of four- and eight-cell human embryos and the establishment of a pregnancy following the freezing and storage of an eight-cell embryo for 4 months in liquid nitrogen. The pregnancy terminated at 24 weeks' gestation due to development of a septic Streptomyces agalactiae chorion amnionitis after premature membrane rupture.