[Extension of the concept of extracorporeal fertilization by cryopreservation of impregnated oocytes].

Cryopreservation of human embryos within in-vitro fertilization treatment was already proposed in 1977 by Edwards and Steptoe. Today, this procedure is used worldwide by several teams as a standard method to enhance the success rate of IVF. In spite of this, there are many disadvantages of the freezing of embryos, furthermore it is legally prohibited in Germany. We report on a new concept for treatment, which includes the freezing of impregnated oocytes after IVF and their transfer in subsequent cycles. From 109 out of 120 patients who were treated with a long acting GnRH analogue or a contraceptive pill before IVF stimulation, "supernumerary" impregnated oocytes could be frozen. Twenty-three pregnancies resulted after immediate embryo transfer, and thirty patients, who returned for the transfer of cryopreserved oocytes, became pregnant. Neither the IVF pre-treatment, nor the stimulation in the transfer cycles of frozen oocytes with clomiphene citrate, influenced the success rate significantly. Combining the 53 pregnancies, a cumulative pregnancy rate of 49% can be calculated per IVF stimulation treatment. This means a doubling of the success rate, compared with routine IVF treatment. Although there are still problems to be solved, as, for instance, the insufficient implantation rate of 7% after the transfer of frozen/thawed cells, we consider cryopreservation of pronuclear oocytes a useful and promising supplement of IVF treatment. There is no further need for the freezing of embryos.