ABSTRACT
Freezing an embryo arrests the chemical processes within it while preserving its cellular integrity by increasing its viscosity. The achievement of pregnancy and live birth rates comparable to those following fresh embryo transfer has encouraged a more liberal embryo cryopreservation policy—going beyond a means of banking surplus embryos to a key tool in preventing multiple pregnancy, as well as preempting ovarian hyperstimulation syndrome (OHSS). Improvement in cryopreservation facilities has meant that reported outcomes following frozen–thawed embryo transfer are no longer deemed to be any worse than those associated with fresh embryo transfer, while obstetric and some perinatal outcomes appear to be better. The current evidence base on success rates following elective embryo freezing and deferred transfer is not sufficiently robust to support a radical change in current practice on grounds of increased reproductive success. There appear to be a number of arguments in favor of elective frozen–thawed embryo transfer.
