Abstract
The present study was carried out to investigate the pregnancy outcome obtained from cryo-preservation of whole sibling blastocyst stage embryos for patients with the risk for severe OHSS as compared to those from transfers of fresh day 5 embryos or the surplus embryos frozen-thawed at the blastocyst stage for patients underwent conventional IVF-ET. Retrospective study. From May 1, 2001 to February 29, 2004, 411 patients participated in our thawing-ET program. During the same period, fifteen hundred and twenty-five patients were underwent freshly transfer of day 5 blastocyst stage embryos (n = 4286; group I) in our hospital. Three hundred and fifty-four patients who failed pregnancy in previous COH cycles received frozen-thawed supernumerary blastocyst stage embryos (n = 904; group II), while fifty-seven patients who did not undergo ET because of the risk of OHSS in previous COH cycles took frozen-thawed blastocyst stage embryos (n = 237; group III). Transferable embryos that developed to the expanded blastocyst stage on day 5 or 6 were vitrified by directly plunging EM-grid loading them into liquid nitrogen following artificial collapse of blastocoele. Vitrification solution was composed of DPBS containing 20% (v/v) hFF, 40% (v/v) ethylene glycol, 18% (w/v) Ficoll, and 0.3 M sucrose. Thawing of vitrified blastocyst stage embryos was carried out by 2-steps on day 3 after ovulation. The transfer of vitrified-thawed embryos was performed on the next day. The viability of each group was assessed through the survival, hatching embryo, implantation, and clinical pregnancy rates as possible. The survival and hatching rates of group III were 84.0% (199/237) and 81.9% (163/199), respectively, which were similar to those 89.9% (956/1063) and 82.8% (792/956), respectively) of group II. However, significantly higher clinical pregnancy and implantation rates were obtained in group III (54.4%: 31/57 and 26.8%: 51/190, respectively) than those in group II (42.5%: 149/351; 19.6%: 177/904, respectively). Moreover, it was of significance to note that the clinical outcomes in group III were significantly higher than those in group I (44.6%: 680/1525; 23.4%:1002/4286, respectively). The present results suggest that when the risk for severe OHSS outbreaks suddenly after oocyte collection for COH cycles, cryo-preservation of whole sibling blastocyst stage embryos should have no hindrance to get conventional clinical outcome. Furthermore, we propose carefully a new program that cryo-preserving all sibling embryos obtained from COH cycle and transferring them into uterus of the next unstimulated cycle, probably improving the take-home baby rate by satisfying with both embryo quality and endometrial receptivity.
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