The traditional strategy in In vitro fertilization (IVF) was to perform embryo transfer following a fresh IVF treatment cycle involving controlled ovarian stimulation of the ovaries. Initially, even without the effective ways of freezing and thawing embryos, it was a strategy born from the necessity, as well as an intuitive thought that freezing would compromise embryo quality. Since that time, when excess to the embryos was first frozen with the aim at replacing them within the uterus in a non-stimulated cycle later on, technological advances have brought to growing numbers of embryos being effectively cryopreserved.
Yet, the default position happens to replace the best embryos in the first fresh IVF cycle in the hope of maximizing the chance of pregnancy. In the last couple of decades, greater knowledge of cryobiology has brought to growing confidence in freezing, which reflects in the growing numbers of embryos frozen each year, in addition to success rates that seem to be almost similar to those associated with a fresh embryo transfer. An embryo cryopreservation is now an integral part of IVF treatment worldwide and underpins fertility preservation and embryo donation programs, in addition to strategies to combat the risks of ovarian hyperstimulation syndrome (OHSS) and multiple birth.
The improvement in the cryopreservation facilities means reported outcomes following frozen-thawed embryo transfer are no longer considered to become any worse than those associated with fresh embryo transfer, while obstetric and some perinatal outcomes seem to be better. Thus, elective freezing of embryos, followed by subsequent replacement in a subsequent non-stimulated IVF cycle, could offer a better way of maximizing success while optimizing safety. This method includes an amount of biological plausibility, however the evidence base is far from secure when it comes to safety and clinical and cost-effectiveness, as the data on fetal macrosomia are potentially of interest and require further exploration. Large, appropriately designed, practical randomized trials with an embedded robust health economic component are needed to supply definitive evidence able to altering clinical practice.