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.
Highlights
Successful egg cryopreservation has many potential benefits to a variety of patients
Long time exposure of eggs in vitrification solution (VS) is better than short time exposure As shown in Table 1, in the present study, twenty cycles used 151 eggs (7.6±1.5 per cycle) vitrified with the short
More patients had blastocyst transfer and cryopreservation if the eggs were frozen with the long protocol When we further analyzed the detailed embryo development, as shown in Table 2, we found that if the short protocol was used, 60% of the recipients had at least one available blastocyst for transfer, and the pregnancy (58.3%) and implantation (41.6%) rates with blastocyst transfer were higher than those (25.0% pregnancy rate and 13.3% implantation rate) without blastocyst transfer that accounted for 40% of the cycles
Summary
Successful egg cryopreservation has many potential benefits to a variety of patients. There are mainly two laboratory methods to freeze human eggs: slow freezing [2] and vitrification [3]. When slow freezing was compared with vitrification, it was found that vitrified eggs had a better survival rate than slow freezing [4,5]. Slow freezing can cause spindle abnormalities [9] in human eggs. These factors have limited wide-spread clinical application of oocyte cryopreservation by slow freezing [8]. Vitrification can cause chromosome misalignment [10] in human oocytes, it has better results than slow freezing if appropriate protocols are used [11,12]. Because vitrification can retain a high survival rate after thawing, it would appear that vitrification will become the main egg cryopreservation technology in the future
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