effect of morphology and blastocyst development on the outcome of single-blastocyst transfer in the in vitro fertilization programme

Background. Multiple pregnancy can be prevented by an elective single blastocyst transfer. The aim of this prospective study was to evaluate the effect of blastocyst development and morphology on the outcome of single blastocyst transfer. Methods. In this study 157 women with single blastocyst transfer were included; their mean age was 33.6 years, range 20–42. Embryos were cultured to the blastocyst stage and evaluated using the Gardner’s classification. An elective single blastocyst transfer was performed in 83 women although 2 or more blastocysts developed (Group 1) and in 74 with only one developed blastocyst (Group 2). Results. In Group 1 (2 or more blastocysts) the pregnancy rate was a significantly higher than in Group 2 (1 blastocyst only) (39.8 % vs. 23.0 %; P < 0.05). After the transfer of a single expanded blastocyst no statistical difference in the pregnancy rate between the two groups was observed (45.5 % vs. 44.6 %). A significantly higher pregnancy rate was found after the transfer of one expanded blastocyst with a good embryoblast and trophoblast morphology compared to the transfer of a single early blastocyst (45.6 % vs. 7.1 %, P < 0.05). Conclusions. After single blastocyst transfer, the likelihood of achieving a pregnancy is higher in women with 2 or more blastocysts developed. And also the likelihood of achieving a pregnancy is higher with an expanded blastocyst transferred with good embryoblast and trophoblast morphology. The blastocyst development is the main predictor of pregnancy, which may reflect the embryonic genetic status.