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(SATURDAY, MAY 17, 2014)
There’s still a lot of confusion as to whether Day 5 ( blastocyst) transfers are better than Day 3 transfers. A lot of patients believe that blastocyst transfers have better success rates.
As IVF lab culture systems improved and doctors were able to reliably and consistently grow embryos in the lab to Day 5, we were very hopeful that this would result in improved pregnancy rates . After all, growing embryos for longer would allow us to transfer them back into the uterus at the “optimal time”. In vivo, Day 3 embryos belong in the fallopian tube and blastocysts belong in the uterus, so that isn’t it logical that mimicking nature would improve IVF pregnancy rates ? While there was a lot of enthusiasm when blastocyst transfer was first introduced ( as is common with any new technique in medicine, which is always greeted with hype and hope), over time we realized that this simplification was not necessarily true.
Let’s consider a Day 3 embryos which is destined to implant. Keeping it for 2 days extra in the incubator and transferring it on Day 5 is not likely to improve the chances of it implanting, so why should we expect that merely growing embryos for 2 extra days in the lab would improve pregnancy rates ?The problem in IVF today is that we still cannot identify which embryo will implant successfully. The major benefit of a Day 5 transfer is that it allows the Day 3 Grade A embryos to “compete “ with each other in vitro, so that we can select the best one more intelligently by observing it for an additional 2 days This allows us to reduce the number of embryos we need to transfer in order to achieve a pregnancy. Thus the major advantage of blastocyst transfer is that it allows us to reduce the risk of a high order multiple pregnancy. Since this is so valuable, then why not just transfer only Day 5 embryos ? Why do some clinics still offer Day 3 transfers ? Some clinics have poor quality labs, and are not able to grow embryos reliably until Day 5. This is especially true for clinics which do “batch IVF” where the visiting doctor is available for only 1-2 days during which he has to complete all the transfers, before he moves on to the next clinic. Some clinics offer the option of a Day 5 transfer, but not routinely for all patients, because the risk is that the embryos may arrest in vitro , so that there are no blastocysts left to transfer on Day 5. This is why these clinics will insist that the patient have at least 3 Grade A embryos on Day 3 if they want to opt for a blastocyst transfer. This minimizes the risk of cancelling the transfer. They want to be sure that they will have at least one embryo to transfer , because cancelling the IVF cycle because there are no embryos to transfer can be emotionally traumatic for the patient, who is likely to blame the IVF clinic for this problem. ( On the other hand, if the clinic does do the transfer and the patient fails to get pregnant, at least she will not blame the clinic for the failure and will attribute it to her bad luck or her destiny). Let’s consider a patient who has only one top quality Day 3 embryo. Should the doctor transfer this on Day 3 ? Or wait till Day 5 ? The doctor may say it’s best to transfer on Day 3, because waiting till Day 5 will not help to improve the chances of success, so why bother ? Also, it’s in the doctor’s best interests to at least reach the stage of embryo transfer, so that patient is happy that she has reached this important milestone. However, I'm not sure this is the best approach for the patient. Once the embryo has been transferred, the patient is subjected to the horrible 2ww. In a bad clinic, which is not confident of its lab facilities, it may make sense to transfer the embryo on Day 3, because the doctor is not sure the lab will be able to grow the embryo to Day 5. However, in a good lab, it makes sense to wait till Day 5. If the embryo is going to arrest , we might as well know this before the transfer, rather than subject the patient to 2 weeks of suspense and misery. By doing a Day 3 transfer, all we’ve done is prolong her uncertainty. Of course, she may be happy that at least her embryos were transferred, and she may even “feel pregnant” after the transfer, but this is short lived happiness. However, if the lab is good, and the patient is mature enough to accept the fact that if the embryo arrested in vitro, it would have arrested in vivo as well (which means she wouldn’t have got pregnant with the Day 3 transfer either) , it makes much more sense to do a blastocyst transfer . This way, rather than always being uncertain as to the reason for the failed implantation, we’ll know that the reason for the failure is because the embryo was not of good enough quality to develop further and become a blastocyst. While the failure to have embryos to transfer can cause considerable short term emotional pain, on a long term basis, it can provide valuable answers, which allow patients to move on with their life. Thus, they can consider using alternative options such as donor eggs in their next attempt, rather than remaining stuck in limbo, and repeating failed cycle after failed cycle.