A comparative study of using the cryotop and cryoloop in vitrification of human preimplantation embryos

Abstract

Objective To compare the effect of vitrification on human cleaved embryos and blastocysts using cryotop and cryoloop. Methods Retrospectively cohort analysis on the documents of 912 frozen embryo transfer (FET) cycles was performed to find out the differences and the potential factors in the embryo developmental and clinical results after vitrification with cryotop and croloop. Results For frozen-thawed cleavage embryos (n=385), no differences were found between the two groups (cryoloop, n=251; cryotop, n=134) in survival rate, fully intact blastomere rate, clinical pregnancy rate, implantation rate, miscarriage rate, delivery rate per transfer, twin birth rate, premature birth rate and ratio of male to female infant. The good-quality embryo rate in fresh (24.78%) and frozen-thawed cycles (40.76%), the number of ET cycles (1.3±0.6), the mean number of frozen-thawed transferred embryos (2.1±0.4) and low birth weight rate (19.01%) in the cryoloop group were significantly higher than those in the cryotop group (18.59%, P=0.002; 28.13%, P=0.001; 1.2±0.4, P=0.001; 1.91±0.41, P=0.000; 4.08%, P=0.015). For frozen-thawed blastocysts (n=527), no differences were found between the two groups (cryoloop, n=251; cryotop, n=134) in the number of ET cycles, survival rate, fully intact blastocyst rate, expanded frozen-thawed blastocyst rate, miscarriage rate, twin birth rate, premature birth rate, low birth weight rate and ratio of male to female infants. However, the clinical pregnancy rate (67.94%), the implantation rate (49.72%), the delivery rate per transfer (52.96%), the good-quality embryo rate in fresh cycles (27.0%) and the mean number of frozen-thawed transferred embryos (1.9±0.4) in the cryoloop group were significantly higher than those in the cryotop group (54.17%, P=0.001; 39.58%, P=0.002; 41.25%, P=0.047; 23.0%, P=0.002; 1.8±0.5, P=0.004). The further binary logistic analysis confirmed that the number of good-quality embryos in fresh cycles, the type of loading embryos in vitrification (cryoloop or cryotop) and the thickness of endometrium were potential factors of clinical pregnancy in vitrification-thawed blastocysts ET cycles (P=0.017, P=0.049, P=0.044). There were no differences in the age, the mean number of vitrification-thawed transferred embryos, the number of expanded vitrification-thawed blastocyst, the number of ET cycles and the type of endometrium. Conclusion Both vitrification-thawed survival and clinical outcome equal between cryotop and cryoloop in day 3 cleavage embryos cryopreservation embryo-transfer cycles; for blastocyst cryopreservation embryo-transfer cycles, the clinical outcomes in cryoloop group are superior to cryotop group. Key words: Vitrification carrier; Cryotop; Cryoloop; Cleavage embryo; Blastocyst