The future of IVF: vitrified-warmed blastocyst transfer

Abstract

Introduction: The development of blastocyst vitrification has significantly changed the approach to embryo transfer. In cases where there is a high risk for developing ovarian hyperstimulation syndrome, all embryos can be vitrified and transferred in subsequent menstrual cycles. On the other hand, vitrification of surplus embryos at the time of transfer allows for higher cumulative pregnancy rates. The optimal method of endometrium preparation for frozen-thawed embryo transfer (FET) still remains uncertain. The aim of this study was to compare the outcomes of vitrified-warmed blastocyst transfers in natural and artificially prepared cycles. Methods: All vitrified-warmed blastocyst transfers performed in the last two years (2013 and 2014) at our IVF centre were included in this retrospective study. In women with predictable and regular ovulatory cycles, FETs were performed in natural cycles without hCG triggering. In patients with irregular and anovulatory cycles, FETs were performed in artificially prepared cycle using the combination of oestradiol and micronized progesterone without GnRH agonist suppression. Patients’ characteristics, treatment parameters and pregnancy outcomes were compared using Pearson's Chi-squared test and Student's t-test. Results: In the study period, 835 vitrified-warmed blastocyst transfers were performed in natural and 278 in artificially prepared cycles. There were no statistically significant differences in patients’ characteristics and treatment parameters between both groups, with the exception of the average number of transferred embryos (1.30 in natural cycles vs. 1.41 in artificial cycles, p < 0.05). The biochemical pregnancy rate observed was higher in artificial cycles (8.90% vs. 17.64%), but there were no statistically significant differences in clinical pregnancy rate (36.03% vs. 34.89%), implantation rate (31.26% vs. 28.94%), abortion rate (14.54% vs. 21.00%) and live birth/ongoing pregnancy rate (30.53% vs. 25.18%) in natural compared to artificial cycles. Conclusion: Vitrified-warmed blastocyst transfers in natural and artificially prepared cycles are equally successful in terms of implantation, ongoing pregnancy and live birth rate. The outcome of vitrified-warmed blastocyst transfer in natural as well as artificial cycles appears to be comparable to blastocyst transfer in fresh IVF cycles.