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Another cautionary note when evaluating studies that compare Day 2/3 transfers with blastocyst transfers (whether they are looking at ICSI or not) is that the same number of embryos are transferred in both arms of the study. It is often the case that more embryos (often up to twice the number) are transferred on Day 2/3 than on Day 5. Thus, they are not comparing apples with apples.
Many of the older studies comparing Day 2/3 v. Day 5 (ICSI or not) were performed using culture systems that are now obsolete. The relatively recent (last 5-6 years) incorporation of FDA-approved sequential culture media systems and more stringent laboratory conditions (i.e. pH control, 02 reduction, removal of airborne contaminants, etc.) have resulted in much more "healthy" blastocysts with significantly improved developmental potential. We are much closer to the "in vivo' environment today than we were 7 years ago. I would say a critical factor in deciding in vitro or in vivo embryo culture (whether ICSI'd or not) is to determine the experience and degree of success your particular lab has with blastocyst culture. Unfortunately, there is still considerable variability between labs with respect to blastocyst culture. You are as unclear as the rest of us and I don't think there is an absolute "right" answer in your case. I know, I know, not much comfort am I?
With regard to the "comeback kids". On several occasions I have observed embryos deemed to have marginal or poor developmental potential on Day 3 make a comeback and reach the blastocyst stage, usually on Day 6. However, not all blastocysts are created equal. The number of stems in the inner cell mass of the blastocyst is of critical importance for future development. It is often the case that these marginal embryos develop to the blastocyst stage, BUT do not contain an adequate number of stem cells for term development. These blastocyst stage embryos, if transferred, often result in "chemical" pregnancies or early miscarriages.
In that particular study, we were really interested in the impact of crappy sperm on blastocyst development, not the effect of ICSI per se. ICSI was more of a complicating variable in our study rather than a separate variable to be evaluated. Crappy sperm mandated the use of ICSI. We did not ICSI with "normal" sperm. Those studies had already been done with ambiguous results (as you found out). What we found (and had suspected) was that when crappy sperm was used for IVF (mandating the use of ICSI), fewer embryos that looked good on Day 3 (as well as those that didn't look good) made it to the blastocyst stage. Those that did make it to the blastocyst stage were of poorer quality (i.e. fewer stem cells) than those embryos derived from conventionally inseminated eggs with "good" sperm. Thus, we determined that just performing ICSI does not "cure" male infertility, although it does improve fertilization markedly in cases with severe sperm problems. Up until then, ICSI was being toted as the "magic bullet" for male inferitilty. All things being equal on the egg side, crappy sperm leads to crappy embryos. We and Denny Sakkas published on the same topic within a few months of each (although we didn't know the other was working on the say track). He found very simmilar results, which was comforting.
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