IVF PGD testing at day 3 or day 5?

[Maisy]

I was wondering if anyone here has done PGD and if the embyro's were tested at day 3 or day 5? (I know this varies between clinics based on their testing methods). From a layperson's point of view is it safe to take cells out of a day 3 embryo where there are only a few, as opposed to hundreds of cells at day 5? I have heard that not as many embryo's can make it to day 5 so they would be higher quality embryos but you would have less of them as opposed to day 3. One clinic I spoke to does this on day 5 and they take the part of the cells that go on to form the placenta which sounds safer to me, but the cost of one cycle is so much more compared to the other clinic which does them on day 3. Has anyone had experience with PGD and what did your clinic do?

[Kmn]

As you say, different clinics do it differently. I think that the skills required for each test are rather different - so it is everyone's interests for the clinics to get very very good at one or the other.

It is safe to take one cell from a day 3 embryo - the downside of this technique is that there is only one cell's worth of genetic material to test, so getting a reliable test is more challenging. In short - the genetic material gets put through something like a gene photocopier to make enough DNA to test. And then they hunt for the defective gene or genes. If the defective gene is absent, then either the embryo doesn't carry it or the gene photocopier didn't copy it. This latter effect is very possible, so for a day 3 embryo test they also have to find linked genes that can be used to test the test. When we used pgd it took 3 years to get the test sorted out (this was a few years ago).

If you have more cells then this is less of an issue, and test development is usually quicker. The downside is that there will be some embryos that don't make it from day 3 to day 5 that might have survived if they were in a uterus rather than a flask. In some ways this is OK - in effect it is screening and putting back the strongest and most likely to implant embryos; but it can be heartbreaking if the only embryos you have don't get to day 5.

I think you said in the other thread that you were screening for general 'older egg' chromosome problems rather than a specific gene - does the more expensive clinic screen for more potential problems?? I don't think that the costs involved in rearing embryos for another couple of days should be particularly high.

[Maisy]

I think you said in the other thread that you were screening for general 'older egg' chromosome problems rather than a specific gene - does the more expensive clinic screen for more potential problems?? I don't think that the costs involved in rearing embryos for another couple of days should be particularly high.

Thanks for replying. I don't remember the other thread, perhaps I wrote it a year or 2 ago but now we would be looking for a specific gene/s and not chromosomes, though one clinic said they can build a test to look for the gene and they can also test 2 more things so they usually do the main chromosome test (its either 13/18/21, can't remember exactly) so we would be looking at a gene as well as chromosome test (only because they can add it in). Our problem though was definately genetic, so the information on the chromosome itself and not the number. My main concern is which clinic has better odds to find what we are looking for. The costs though for the cycles based on 2 clinics are quite different for each step of the process. The 3 day clinic we could do 2 cylces, but the 5 day clinic the cost is a lot more that we could only afford to do one cycle.

[melbel]

Another option with PGD to think about is to do two stimcycles back to back or close together and freeze the first one, then add the embryos together for the PGD as the cost is the same no matter how many embryos they are testing....MIVF now offer this as an option to keep the costs down.

[JoeSpratt]

we did testing on day 3 embies - only had 6 to test and got results on 3 with only 2 unaffected. As Kmn said above I think the efficiency of testing earlier would come down to the skill of the embryologist and the robustness of the clinical testing. They always run controls and that is why the initial setup of testing for each particular gene/chromosome defect can take so long. They need to know that the testing is robust and reproducible.