Single instead of double day-five blastocyst transfer maintains the same clinical pregnancy rate and decreases multiple pregnancy and abortion rates in fresh IVF cycles

Abstract

The main objective of this study is to reduce multiple pregnancies and abortions without modifying the clinical pregnancy rate in fresh IVF cycles by transferring single day-five blastocysts A retrospective analysis of three embryo transfer strategies for all patients enrolled in a fresh IVF cycle between October 2015 and December 2017. We compared Group 1 (G1) 93 double cleavage stage embryo transfers, Group 2 (G2) 39 double blastocyst stage embryo transfers and Group 3 (G3) 259 single blastocyst stage embryo transfers. The variables analysed were clinical pregnancy, multiple pregnancy, abortion and implantation rates All fresh IVF cycles included in this study were incubated in K-System® G-185 or ThermoFisher Scientic® Heracell 150i incubators with Sage® or Global Total® Mediums. Chi square independence test and Fisher's exact test were used to compare clinical pregnancy, implantation, multiple pregnancies and abortions rates between the three groups. When independence tests were significant, parametric and non-parametric comparison tests were used in pairs. Additionally, the odds ratio obtained for each variable was reported Results showed that there is no statistical difference in clinical pregnancy rates when transferring embryos in the cleavage or blastocyst stage (p-value=0.8352). However, there is an important reduction in the multiple pregnancies achieved when transferring only one blastocyst (1%) compared with double embryo cleavage stage transfer (33%) and double blastocyst stage transfer (33%). The independence between groups and multiple pregnancies was rejected (p-value<0.0001). The comparison of proportions were significant between G1 and G3 (p-value<0.0001), and between G2 and G3 (p-value<0.0001). In addition, as we expected the implantation rate was highly improved when only one embryo in the blastocyst stage was transferred (41%) in comparison to two blastocysts (26%) or two cleavage embryos (24%) transfers. The independence was rejected (p-value<0.0001). The comparison of proportions were significant between G1 and G3 (p-value=0.0007), and between G2 and G3 (p-value=0.0375). The odds ratio for implantation rates obtained, with G1 as reference, were 1.1129 for G2 and 2.0967 for G3. Finally, the decrease in the abortion rate was striking, 20% for G1, 5% for G2 and 10% for G3. There is not a statistical significance among the groups (p-value=0.1352), however, these proportions show a tendency, transferring in blastocyst stage suffers fewer abortions than in cleavage stage. The main limitation of this study is the difference in the number of patients in each group We conclude that single day-five transfer in fresh IVF cycles decreases multiple pregnancy and abortion rates and increases implantation rates without affecting the number of clinical pregnancies achieved