PGS – Preimplantation Genetic Screening

PGS, PGD, CGH – they do all actually mean something different and are used in different cases but essentially they also all refer to the same outcome and that is the genetic testing result of an embryo.

At our previous clinic the method they used was CGH which is an array test. We are not using that method this time.

This time, at our new clinic, we are going for the Next Generation Sequencing which is thought to be slightly more accurate and my clinic refers to it as PGS.

Apparently the CGH method is the preference for when they are working with gene translocations (which we are not) but for everything else it is this Next Generation Sequencing.

Today I had the information session to discuss it all with the scientist and I really did learn some very interesting things – more than I did at the old clinic I think.  I don’t know if this has to do with the fact that I am more widely read on it this time so I had better questions but my understanding now is far greater than what it was before the session, despite having genetic testing carried out on embryos previously.

PGS and error rates

There is a lot of discussion out there about error rates and non viable embryos actually becoming babies and obviously this idea freaks people out. I mean if you are going to test and then an abnormal can be a baby and it ends up being thrown away instead, I mean you’d want to be asking…what the actual fuck?

So here’s what I got from the session today.

• The error rate is in the region of 2-5%. My clinic quotes 95% accuracy on the all the forms but they believe it to be closer to the 98% mark (how they measure accuracy I don’t know – I wish I’d remembered to ask while I was in there). So if you say 95% that’s 1 in 20 where the outcome will be wrong.
• Wrong doesn’t always mean that you are discarding an embryo that was read as abnormal when it is actually normal. Wrong can also mean you keep an embryo that is measured as normal when it is actually abnormal. Wrong works both ways and i hadn’t considered that before.
• If you go check out Braverman’s website (dude who is doing a lot of work with silent endo) it says they try to transfer as many embies as possible (I’m not sure if this means they will transfer those with an abnormal result but that’s what it is implies). If the pregnancy sticks they will go on to do a CVS (invasive test at 11-14 weeks with 1% miscarriage risk) which is more accurate than the PGD testing.  There is a thought by this group that abnormal embryos can autocorrect.
• I specifically asked my clinic about this scenario. Firstly, in Australia they cannot transfer known abnormal embryos. It’s not a legal thing per se, but more that they would lost their accreditation if they were to do this. Secondly, the scientist seemed to think that the auto correct thing was less likely and that it was more to do with the error rate of the testing. Apparently there are some situations where you will draw a biopsy from one side of the embryo and that will give a normal result, draw it from the other and you will get an abnormal result. That’s just a developmental thing and there’s not anything you can do about it.
• Because of the error rate my clinic recommends that on positive pregnancy a Harmony test be carried out, obviously the 12 weeks scan + bloods and then if there is any sort of high risk result from either of those then go on to have a CVS (11-14 weeks, 1% miscarriage risk) OR amniocentesis (must be min of 15 weeks I think and 0.5% miscarriage risk). The issue with those laster tests clearly being the miscarriage risk and then also the thought of having to deal with a distressful outcome when you are so far along in the pregnancy. I really hope we don’t have to walk THAT particular road.

So that is all interesting and food for thought. We will still do the testing despite the error rate. And we will certainly do the Harmony test plus the standard 12 week scan for nuchal fold measurement yada yada.

Other interesting info

There were a few more interesting thing pointed out today which I didn’t realise.

• You can get perfect looking embryos that simply aren’t suitable for biopsy – usually because the inner cell mass (the baby part) is too close to the biopsy point (they do assisted hatching at day 3 and and biopsy through this hole on day 5 or 6). If the mass is too close it means they’d take parts of the baby and they don’t want to do that. It’s meant to be placenta only. If we had one like this then we could transfer without testing but that would be our only option.
• You can get embryos that don’t make blast by day 5 but haven’t arrested. In this case I can also opt to transfer rather than wait and see.
• You can do everything right and the embryo just doesn’t cope with the biopsy in which case it dies before you even get a result, or even worse, it dies when thawed for transfer. Imagine if you had one normal result and that fucker died on the thaw. You’d be devastated.

I really felt like there were more options of what might happen when discussing all this with the clinic today – it wasn’t just a “well these are ok to biopsy and we’ll chuck the rest” scenario. I feel like I might have transfer options too. Maybe. At least that the scientist would be looking for those options for me. Like I said before though, perhaps my understanding of the whole thing is just a little different these days. I know more and I’ve been through it so I get it a little better.

I guess we will see what happens when the eggs drop in about a month. Hopefully I make it without debilitating stomach pain. Ha!