ABSTRACT
The use of superovulation techniques to Improve and simplify human in vitro fertilization (IVF) led to the problem that large numbers of oocytes, and consequently embryos, would be produced. A possible alternative would have been to perform IVF in spontaneous cycles after having triggered ovulation by exogenous human chorionic gonadotrophin (hCG). The results however remained poor,1,2 occasionally interesting,3 but useless in routine. Other solutions would have been to limit the number of oocytes recovered or inseminated or to discard the embryos in excess of the number appropriate for a safe transfer avoiding the risk of multiple pregnancies. These alternatives are either unethical or lead to a decrease in the overall efficiency of IVF, which, finally, is also unethical. Such considerations initiated the development of embryo freezing in humans.
