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There are very different schools of thought as to whether to perform Day 3 or Day 5 Blastocyst stage embryo transfer. In our lab, we feel we are capable of identifying the best embryos on Day 3 and from 1996 until January 2011 most, if not all, of our transfers have been done on Day 3. At the end of 2010 we began doing more Day 5 transfers following a very strict decision criteria for "pushing" to Day 5. Not all Day 2 or 3 embryos can develop to a blastocyst with a loss of about 45 - 60% of your embryos as they are cultured the extra 2 or 3 days. Therefore, those embryos that do make it to a blastocyst for transfer on Day 5 are considered the best or hardiest and is a natural selection process. The problem that arises is that there may be nothing to transfer back. This is why we have the criteria we have in deciding which day to do the transfer.
On Day 2 after Retrieval we can more accurately make decisions on whether to schedule a transfer on Day 3 or Day 5 based on the number of "good" quality 4-cell embryos are developing when the embryos are evaluated. For patients under 37 years old we need at least 5 good quality 4-cell embryos. Some clinics require more than 5, but 5 seems to work for us. We re-evaluate on Day 3, at this time we need 3 good quality 8-cell embryos to continue going to Day 5. If these criteria are not met we will schedule the transfer for Day 4.

Now that day of transfer has been discussed, now number of embryos to transfer needs to be approached. At The Center for Reproductive Medicine, we follow the ASRM guidelines of 2 embryos in patients under 37 years old; 3 embryos in patients 38-39 years old; and, 4 embryos in patients 40 and older on a Day 3 transfer. For a Day 5 transfer this number can be reduced by 1 embryo and should be reduced by 1 embryo in patients that are under 35 in order to reduce the potential for multiple pregnancy risks. If the embryo quality is poor or if there have been previous failed IVF cycles the number transferred can be adjusted after thorough discussion with the physician.