Friday, February 10, 2017

Why transferring a single blastocyst at a time improves pregnancy rates


Lots of IVF patients and doctors are very confused about how many embryos to transfer. The general belief is that the more the embryos you put back, the better your chances of getting pregnant. This is why many IVF doctors still put back as many embryos as the patient has. If the patient happens to end up with a multiple pregnancy , they are happy to do an additional procedure called a selective fetal reduction, to reduce this to a twin pregnancy. This practice is so rampant, that some ultrasound clinics do 3-7 fetal reductions daily  !

Patients also contribute to this push for transferring more embryos. This is especially true when they have failed multiple cycles . They feel that if all the embryos which had been put back so far haven't implanted, then why not transfer even more , to increase their chances. They naively believe that their chances of ending up with a high order multiple are very low, so they feel that they will cross that bridge if and when they get to that stage.

This is something which IVF doctors encourage as well , because they want to boost their success rates. They want as many of their patients to get pregnant as possible, because a pregnancy is an IVF specialist's endpoint. If it does turn out to be a multiple pregnancy , then that's really the obstetrician's problem, not theirs ! They can tell the patient - I did my bit - I got you pregnant , which proves I am a good IVF doctor ! They want to artificially inflate their IVF success rates, because this allows them to trot out statistics which keep on getting progressively better, even if the live birth rate suffers. This is especially true in clinics where pregnancy rates aren't very good, because their laboratory conditions are sub-optimal, which means their implantation rates are poor.

The good thing about IVF technology is that it advances relentlessly. Our ability to grow embryos to the blastocyst stage is now excellent , and high quality blastocysts have a very good chance of implanting and becoming babies. Even better, our ability to freeze these blastocysts  has become so good ( as a result of vitrification ) that we never need to waste any of these precious embryos.

In the past, because the IVF lab wasn't robust enough to grow embryos to blastocysts reliably; because freezing programs weren't good; and because implantation rates were poor , a lot of clinics would transfer three, four, and even five embryos on day two or day three. It was pretty much a spray and pray approach. Since IVF was a hit and miss affair , the attitude was  - let's put in whatever embryos we have , and we'll see what to do in case she gets pregnant. If she ends up with a high order multiple, we'll handle the complication if and when it occurs.

Over time, as the embryology laboratory kept on improving, high order multiple births became so common, that IVF clinics realised that they had to do something to prevent this problem. This is why many clinics are now moving to transferring only two embryos on day five.

In fact , our suggestion to our patients is to transfer only a single embryo - less is more ! Suppose you have  two high quality blastocysts. One choice is to put both these blastocysts back together . You could get twins, which is perhaps not such a bad outcome , but twins do have a higher complication rate as compared to singletons. The other alternative is to transfer one in the fresh cycle; and freeze one. Finally, you could freeze both.

In the past, we would say - Go ahead and transfer both . However, our recommendation is to transfer only one and freeze the other. If an embryo is going to implant, then it will - putting two together at one time doesn't increase the chances of implantation - it just increases the risk of a twin pregnancy.

Transferring two blastocysts together doesn't improve the chances of either implanting, because each embryo is independent . Transferring more than one does not have an additive effect.  Think of each blastocyst as being a 5 carat diamond solitaire - each solitaire is best mounted separately, because it shines better on its own. This is why egg and embryo pooling is such a stupid idea.

Even if the single embryo doesn't implant , then at least you have a second shot at getting pregnant by transferring your frozen embryo in the next cycle. And there's no reason to think that transferring two would have improved the chances of a pregnancy. In fact, if the cycle failed, then you would have ended up losing both, and would not have anything in reserve to fall back on.

The additional cost of a frozen cycle is so much less than a fresh cycle, that it's far more cost effective to use this approach. In fact, for mature patients , we are now going one step further and saying - Freeze all your embryos , and then transfer only one embryo back at a time. Transferring frozen embryos actually has a better implantation rate because we can prepare the endometrium so that it's optimal for receptivity.

This way, patients get multiple chances to get pregnant from just a single egg collection. This means their cumulative conception rate over multiple cycles with these frozen embryos is far better. The only downside is that it takes longer to get pregnant , because the patient needs to come back for her frozen cycles. However, not only do the overall pregnancy rates improve , the chances of her taking a baby home increase as well, because the risk of obstetric complications is reduced with a singleton pregnancy , as compared to a twin.  Also, if she gets pregnant, she can use her frozen embryo to have a second baby in the future as well , thus completing her family !

Paradoxically, a single transfer if even more important in patients with poor ovarian reserve, who have very few embryos. Each embryo is worth its weight in gold, and should be transferred individually. Even if she has only a single top quality blastocyst, a freeze all is the best approach. Of course, this is applicable only if your IVF clinic has a high quality lab and a robust vitrification program. This is why selecting a high quality IVF clinic makes such a big difference to your chances of having a baby !



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