Frozen pronuclear oocytes: advantages for the patient

Since the first reported pregnancy in a human being after a frozen/thawed eight cell stage preembryo, cryopreservation of preembryos has been integrated as an important element of assisted reproductive technologies (ART). The cryopreservation technique has brought several advantages to ART. It allows the transfer of a limited number of embryos in the collection cycle, thereby reducing the risk of multiple pregnancies, and the patients have a reservoir of excess embryos for additional transfers. This maximises the number of embryo transfers per oocyte retrieval, while at the same time increasing the cumulative pregnancy rate from a given treatment cycle. Also, the ability to freeze all the embryos obtained and transfer at a subsequent cycle is useful in the avoidance of hyperstimulation syndrome, or when factors that may jeopardize implantation are apparent. Freezing of oocytes in a pronuclear stage has a valuable role in the management of infertility. Supernumerary zygotes can be cryopreserved safely for future transfer, avoiding additional inconvenience for the patients. The freezing thawing technique does not have any adverse effects on oocytes fertilized microsurgically. Pronuclear stage oocytes eventually survive the cryopreservation procedure better, yielding after culture cleaved embryos appropriate for transfer, which could increase the implantation rate. We believe that the cryopreservation of cleaved embryos, which is problematic, can be safely replaced by this procedure. This is not only an advantage for society as a whole, but also for the people involved in the process, as there should be no ethical or moral conflict for the patients or for the laboratory staff about discarding this material.