Abstract

In vitro fertilization (IVF) as a clinical method has remained quite ineffective despite tremendous scientific efforts to improve its efficacy. Because of the low likelihood of an individual embryo to implant, more than one embryo is transferred to the womb per treatment cycle to increase the chance of conception. As a result, however, the incidence of multiple gestations in IVF patients is unacceptably high. This in turn has prompted a clinical trend towards reducing the number of embryos transferred per embryo transfer (elective single embryo transfer). A reduction of the number of embryos to be transferred depends on the following prerequisites: First, the cryopreservation technique should allow reliable freezing of supernumerary oocytes at the pronuclear stage or embryos with a survival rate high enough not to compromise the fertility potential resulting from the pool of oocytes that is retrieved per single oocyte pick-up; second, the increased financial costs, burden, and health risks that result from the additional effort of transferring frozen-thawed embryos need to be balanced with the benefit of reducing the number of transferred embryos, which is a reduced incidence of twin and triple pregnancies.