Today, our standard practice is to freeze all your embryos at a blastocyst ( Day 5) stage, and then transfer them after thawing them in the next cycle, one at a time. Here's why we think this is the best method for optimizing your chances of having a healthy baby.
Let's start off with why we don't advise doing fresh transfers. The chances of getting pregnant depend on two variables - 1. the quality of the embryo, and 2. endometrial receptivity.
In a natural cycle, endometrial receptivity and the embryo are synchronized perfectly, which is why fertile women get pregnant in the bedroom so easily. However, in a fresh IVF cycle, because we're super-ovulating you, our focus is on getting you to grow lots of good quality eggs. However, this often means that the price we pay for this is that your endometrial receptivity gets impaired. The truth is that it's hard to have your cake and eat it too, which means we need to compromise when doing an IVF cycle. This is why, even though we get great quality embryos, they may not implant. Now this is true even though the endometrium looks fine on an ultrasound scan , and this is because its receptivity at the molecular level has taken a beating , because of the high levels of hormones to which the endometrium has been exposed to during the fresh cycle.
This is why we think freezing all the embryos, and then transferring them later on, is a better option. This allows us to focus on one thing at a time. In the first fresh cycle, we focus on your super-ovulation protocol, to get lots of eggs and good quality embryos. Then, in the second thaw cycle, we can focus on your endometrial receptivity , because we already have good quality frozen embryos , and we just need to transfer them. Thanks to our embryologist's extensive experience and expertise with vitrification, our success rates with freezing and thawing embryos is practically 100%, which means no harm is done to your precious embryos as a result of the freezing and thawing.
Why do we prefer transferring a single blastocyst , as compared to transferring two embryos ? I think we all should agree that transferring more than two is irresponsible , because it just increases the risk of a high order multiple pregnancy. This is dangerous for the babies, because of the risk of prematurity ; and doing procedures like selective fetal reduction to salvage the situation often means that you may end up miscarrying and losing all your babies - something for which you will never forgive yourself !
If I had to pick between one and two, I would still advise one. Now, this, again, is not intuitive because lots of patients say, " A twin pregnancy is fine - it's actually a bonus, because I get an instant family ! What's wrong with putting two back?"
Let's look at this logically. Each embryo has its own independent chance of getting pregnant. Let's assume that if we put one top quality blastocyst back in an optimally receptive endometrium, it has a 30% chance of becoming baby.
Now if we put two embryos back at the same time, each of them has that 30% chance, and the limiting factor is endometrial receptivity. If the endometrium is optimal, then there is high possibility that both may implant, which is why the twin pregnancy rate is high after IVF. Now the reason why only one implants ( and the other doesn't, even though the uterine lining is receptive) is because one of the blastocysts has some kind of genetic problem, which prevents it from implanting. It's impossible to identify this in the lab, and this is why transferring two blastocysts has a better pregnancy rate than transferring just one - you are improving the chances of transferring a genetically normal embryo by putting back two instead of one.
On the other hand, it's possible that when we transfer two genetically normal blastocysts, neither of them will implant because there's a problem with endometrial receptivity. This means no matter how many blastocysts we transfer, none of them would implant. If we put two at a time, we have wasted both these precious embryos. On the other hand , if we put one at a time, each embryo has its own chance of becoming a baby, because the endometrial receptivity may be better in one cycle as compared to another. This way, we are maximizing the probability of achieving a pregnancy for these women , because we are making the best possible use of these blastocysts. I agree this sounds very hit and miss, but sadly these are the current limitations of IVF technology today, and ERA and PGS do not help in overcoming these.
The truth is that each blastocyst is worth its weight in gold , and should be given the best possible chance of becoming a baby. The best way of doing this is by transferring one single blastocyst at a time in an optimally prepared endometrium. Yes, this does have disadvantages , because it does mean that the patient needs to come back again for the next cycle, in case the first one fails.
However, the good thing about transferring frozen embryos after thawing them is that this is a simple procedure , which is not expensive. The patient doesn't need to take any injections and it can be done in a natural cycle as well. Because we can focus on optimizing both the embryo as well as the endometrium , because we're doing these independently, the overall chance of achieving a pregnancy is much better.
I think this is what patients need to focus on - the cumulative conception rate, so that their chances of taking a healthy baby home is maximized.
Is your doctor suggesting you transfer many embryos ? This suggests he has no confidence in his IVF lab, and you should look for another IVF clinic !
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