Most embryo transfers at Pacific Fertility Center are done with blastocyst stage embryos. (pacificfertilitycenter.com)
«In fact, most embryos fail to successfully implant and the pregnancy ends.» (sciencedaily.com)
According to the NIH, most embryos used are leftover from in vitro fertilization clinics, and have been designated for research with the «informed consent of the donors.» (thinkprogress.org)