Hi! I'm new to this message board. I have been lurking for a few days but haven't posted yet. We our first IVF cycle in 2004 (failed) and are trying again this summer sometime. We did a 3 day transfer and I have read pros/cons to 3 vs 5 day transfers. This may be a dumb question but why do they never do 4 day transfers? Just a thought I had late last night and thought I would ask!
Elizabeth
failed IVF ICSI 2004
Going for second cycle summmer 2008!
On day 4 a good embryo will usually be "compacted" into what is called a morula. This is a fascinating stage of development, where the cells communicate chemically before deciding which of them will do which job the following day. The morula is seldom transferred (not "never", just seldom) because it has little distinct structure to use for evaluation. In other words, it's much easier to grade cleavage stage (day 2 or 3) embryos by observing individual cells and fragments, or blastocyst stage (day 5 or 6) embryos by observing structure (trophectoderm and inner cell mass).
A lot of clinics schedule day 5 transfers regardless of embryo development rate. Those clinics often transfer morulae, as some patients will have embryos that have not yet begun to expand. Other clinics transfer on the day that blastocysts form, whether day 5 or 6 (or rarely, 7). Day 6 blastocysts are by far the most common, although day 5 are preferentially selected for transfer if any form on day 5.