The effect of single embryo transfer in a human vitrified-warmed program

Abstract

OBJECTIVE: A multiple embryo transfer increases the chances of conception from vitrified-warmed blastocysts, but it might result in multiple pregnancies. Accordingly, a single embryo transfer is suggested to reduce multiple pregnancies. This study was performed to investigate how a single embryo transfer has an influence on the implantation and pregnancy rates in a vitrified-warmed program. DESIGN: Retrospective study. MATERIALS AND METHODS: The study included 2,126 cycles from November 2002 to June 2007. The embryos developed to the blastocyst stage were vitrified using EM-grid following artificial shrinkage. The solution for vitrification was prepared according to a previously described method (Lee et al., 2007). Embryo warming was conducted by two steps on day 3 after ovulation. The survived blastocysts were transferred into uterus. The clinical pregnancy and implantation rates per ET were examined according to the number of transferred embryos: consisted of the patients in which a single blastocyst was transferred (group1), two blastocysts were transferred (group2) and three blastocysts were transferred (group3). RESULTS: The implantation rate in groups 1, 2 and 3 was 24.2% (58/240), 23.5% (339/1,440), and 23.2% (821/3,536) and did not differ significantly. The corresponding clinical pregnancy rate in groups 1, 2 and 3 was 22.9% (55/240), 38.5% (277/720), and 50.1% (559/1,116), which was statistically significant (p<0.05). The percentage of twin and multiple pregnancies were 22.7% (63/276) and 0.0% (0/276) in group 2 and 24.0% (133/555) and 11.7% (65/555) in group 3. In this study, embryo transfer was not conducted for fifty cycles with no blastocysts survived. CONCLUSIONS: These results suggest that the transfer of two or more vitrified-warmed embryos increase the conception rate, but has no beneficial effect on the implantation rate compared to a single embryo transfer. Furthermore, single embryo transfer minimizes the multiple pregnancy risk due to several chances of a single embryo transfer per ovum pick-up.