This is one of a series of news items from abstracts of studies presented at the 2013 Annual Meeting of the American Society for Reproductive Medicine as complied by Dr. David Meldrum, former partner and Scientific Director of Reproductive Partners. We appreciate the enormous amount of work it takes to compile and comment on these abstracts.
In a fresh IVF cycle when embryos that have not reached the full blastocyst stage are transferred fresh we expect a lower pregnancy rate. But why is that? Is it that the slower growing embryos do not have what it takes to implant and become a successful pregnancy or is the slower growing embryo out of phase with the normally advancing endometrium?
An abstract from ASRM 2013 gives a reassuring answer to that questions and adds another benefit to freezing all embryos and transferring in a frozen cycle (FET).
Embryos that were not full blastocysts (morulae or early blastocysts) transferred on day 5 or on day 6
after full development had significantly reduced ongoing implantation. But with FET, the implantation rates were the same as for embryos that were expanded on day 5.
The authors believe (as communicated to Dr. Meldrum) that the reduced implantation is the result of slower embryos out of phase with the advanced endometrium of the fresh stimulated cycle.
That difference can be corrected for in a frozen cycle by preventing the endometrium from being too advanced for the growth rate of the embryos.