Optimized protocol for cryopreservation of human eggs improves developmental competence and implantation of resulting embryos

Abstract

BackgroundSuccessful egg cryopreservation has many potential benefits to a variety of patients. However, a superior standard protocol describing all aspects of oocyte cryopreservation has not yet been identified. Oocyte cryopreservation is still a technical challenge for many infertility clinics. To maintain satisfactory clinical outcomes, there is a need to develop an easy to use, yet efficient laboratory protocol. The present study was designed to examine if human embryos resulting from eggs frozen with an optimized vitrification protocol have similar developmental competence as those from fresh eggs.MethodsTwenty recipients received donated eggs vitrified with a protocol in which short exposure time to the vitrification solution was used and 23 recipients received donated eggs and 6 patients had their own eggs vitrified with a modified protocol in which long exposure time to the vitrification solution was used. After warming, egg survival, fertilization, cleavage, blastocyst formation, clinical pregnancy and implantation rates were compared. The developmental competence of eggs vitrified with the optimized protocol was further compared with fresh eggs donated from the same donors.ResultsThere was no difference in the oocyte survival, fertilization, cleavage, clinical pregnancy or implantation rates between the short and long protocol groups. However, blastocyst formation rate was significantly (P < 0.001) higher in the long protocol group (50.8%) than that in short protocol group (26.5%), resulting in more blastocysts being transferred and frozen. When frozen eggs vitrified with long protocol and fresh eggs from the same donors (12) were compared in 39 recipients, no differences were observed in terms of fertilization (86.4 vs 80.1%), blastocyst formation (50.0 vs 59.2%), clinical pregnancy (63.2 vs 60.0%) and implantation (41.7 vs 44.7%) rates. Four out of 6 patients had ongoing pregnancy after transfer of embryos from their own frozen eggs with a 46.2% implantation rate.ConclusionsThese results indicate that blastocyst development is an appropriate measure for egg survival after cryopreservation and frozen eggs have similar developmental potential as fresh eggs if they are frozen with an optimized method.

Assessment of aneuploidy formation in human blastocysts resulting from cryopreserved donor eggs

“…Similar to previous studies [ 1 - 7 ], the present study indicates that high survival rates can be obtained after eggs were cryopreserved with vitrification. Also, high blastocyst development and embryo implantation rates were obtained with the vitrified/warmed donor eggs.…”

“…Egg cryopreservation has become one of the key assisted reproduction technologies (ART) in humans [ 1 - 7 ]. Successful egg cryopreservation has allowed for the establishment of frozen egg banks [ 8 - 10 ].…”

“…Successful egg cryopreservation has allowed for the establishment of frozen egg banks [ 8 - 10 ]. A few studies have reported high clinical pregnancy and live birth rates after transfer of the resulting embryos with vitrified/warmed human eggs [ 7 - 11 ]. It has also been reported that embryo development, clinical pregnancy and embryo implantation rates are similar between fresh and cryopreserved eggs in some egg donation programs [ 7 , 12 - 14 ].…”

“…A few studies have reported high clinical pregnancy and live birth rates after transfer of the resulting embryos with vitrified/warmed human eggs [ 7 - 11 ]. It has also been reported that embryo development, clinical pregnancy and embryo implantation rates are similar between fresh and cryopreserved eggs in some egg donation programs [ 7 , 12 - 14 ]. There was no apparent increase in congenital anomalies [ 15 ] and other abnormities [ 4 ] in the babies derived from frozen eggs.…”

Cryopreservation of mammalian oocytes and embryos: current problems and future perspectives

“…In this regard, it has been suggested that the time should be less than 10 s [127]. On the other hand, a short equilibration time for oocytes in the vitrification solution results in low survival and blastocyst formation rates [128,129]. This observation suggests that, in the short protocol, intracellular water may not be completely replaced by CPAs in the oocytes after exposure to the vitrification solution, and may contribute to damage of some organelles inside the oocyte.…”