Purpose: to determine whether the transfer day or the stage that the embryo is transferred interferes in pregnancy and implantation rates. Methods: oocytes we recovered from 107 patients and submitted to in vitro fertilization. The embryos were cocultured on Vero cells and transferred on day 3 or day 5 post-fertilization, after morphological assessment. Results: the implantation rate of the transferred embryos on day 5 was significantly higher than when the embryos were transferred on day 3, but the pregnacy rates did not change. However, a significant difference was observed in the pregnancy rates for embryos transferred at the expanded blastocyst stage (70.6% of pregnancy) when compared to 20.0% and 10.5% at the earlier blastocyst and morula stages, respectively. Conclusions: the implantation and pregnancy rates were significantly increased when the embryos were transferred at the expanded blastocyst stage, but the culture media and culture conditions now available are not able to provide a satisfactory rate at this stage.
Infertility; Male factor; In vitro fertilization
