We know that embryos don’t always become babies, but patients would like some sense of what their chances of success are, with the particular embryo we have transferred for them . Thus , we know that blastocysts have a better chance of implanting, as compared to Day 3 embryos; and that top grade blastocysts ( for example, those which are hatching) have a better chance of achieving a pregnancy.
The problem is that the only way we can grade blastocysts today is by looking at them under the microscope. This is a pretty crude technique, because even if two blastocysts look exactly the same, they may have completely different implantation potentials, and this is one of limitations of embryo grading.
After all, looking at an embryo just provides us with an snapshot image, and we are much more interested in the timeline of the embryo because we want to predict its fate. We want to be able to estimate the future of this embryo - whether it will implant and become a baby or not - and this is why a single picture captured at a given instant is not enough.
We need to know much more about the history of the embryo if we want to be able to do a better job. The key question is - what is the quality of the egg which this embryo come from? Thus , let's assume we have two identical embryos, one of which has come from a 25 year old woman, and the other from a 40 year old woman. Even though the two embryos look identical, the implantation potential of the embryo from the younger woman is far higher. Explaining this can be very frustrating for the older patient, who may be on top of the world that we have been able to create a picture-perfect blastocyst for her. The truth is that no matter how good our IVF lab is, and not matter how perfect her embryo looks, her egg quality still plays a very important role in determining the implantation potential of her embryo( Incidentally, sperm quality has practically no role to play whatsoever, and it is not something we need to worry about when we do ICSI. )
Similarly, embryos from poor ovarian responders have a much poorer chance of implanting. This can cause a lot of heartburn for these patients. When you have a patient with poor ovarian reserve, and you can manage to transfer a top a quality embryo for her, everyone is on top of the world. However, the very fact that she has required a high dose of injections in order to grow enough eggs to get a high quality embryo itself means that the implantation potential of this embryo is compromised. The best analogy I can give is of two cars , both of which are cruising at 20 miles per hour. Now if one car is in first gear, you know that car is performing well; but if the other car needs to be pushed into fourth gear in order to get it to go at 20 miles per hour, you know there is a problem in the engine of the second car , and you are not likely to buy it.
The truth is that there are lots of intangible biological variables involved in embryo development. Since we still cannot track or measure these, we end up doing a poor job of predicting which embryos will implant successfully. While we can do our best to use superovulation protocols which maximise the number of high quality eggs we can collect; and while we can try to optimize culture conditions to be kind to the embryos, the truth is that if that gorgeous embryo has a genetic defect , because it’s come from a poor quality eggs, or an old egg, there is nothing we can do to repair that.
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