Blastocyst transfer: does it really affect the outcome?

Blastocyst transfer is of great interest to most assisted reproductive technology clinics. The ability to select the best embryos to transfer in order to increase pregnancy rates, and to replace lower numbers of embryos to reduce the likelihood of an unwanted multiple pregnancy have both been realized. The optimal method to prolong embryo culture up to day 5 or 6 is still to be identified, although present techniques offer acceptable blastocyst development rates. Freezing of supernumerary blastocysts is still a matter of discussion, as adequate results are still awaited.