New Series: Q From U: biopsy

Hi Readers,

I am starting a new series, called Questions from You (Q from U), in which I answer some of the common patient questions I get from my contact email.

Recently, I seem to be getting more questions about embryo biopsy for PGD. In the beginning, PGD biopsy meant biopsy of one (or at most two) cells from the 8-cell embryo on day 3 of culture.  Day 3 biopsy is being replaced by  biopsy of  trophectoderm cells from the blastocyst-stage embryo on day 5 of culture.  The trophectoderm cells line the inside wall of the blastocysts and provide cells to the future fetal part of the placenta and not the fetus itself. Trophectoderm biopsy is becoming more popular because more cells can be sampled at this later stage, making the genetic test results slightly more reliable. The test is more reliable because there is more material to assay and a stray rogue cell won’t give unrepresentative results for the embryo (a phenomenon called genetic mosaicism). The other structural feature of the blastocyst is a collection of cells in the inside of the embryo ball called the inner cell mass or ICM. The inner cell mass contributes cells to the future baby and is not biopsied. Your embryo must be a blastocyst and by definition, have these two structural regions (inner cell mass and trophectoderm), to be a candidate for trophectoderm biopsy.

 

 

 

 

 

 

 

 

This patient’s question had to do with her clinic’s practice of waiting until the blastocyst spontaneously hatches to do the biopsy. At her clinic, if it didn’t hatch, it didn’t get biopsied. It could be biopsied on either day 5 or day 6 of culture, provided it was starting to hatch. If the embryo didn’t hatch by day 6, it was discarded.

Her questions were:

Why is my clinic doing the biopsy only on hatching embryos?

If my embryo didn’t hatch on day 6, is it really not viable?

Why would a clinic require that blastocysts be partially hatched  to do the biopsy? Frankly, because it is easier for the technician. If the embryo is already half hanging out of the zona, the tech needs to merely remove a piece of the trophectoderm that is already exposed. It is harder to make a hole in the zona and reach in and pull out part of the trophectoderm to biopsy.  Skilled techs can do it both ways but many of the training classes teach to wait for hatching to do the biopsy so their trainees can hit the ground running and offer the service ASAP.  Some clinics will make a small hole in the zona  on day 3 to assist spontaneous hatching so that hopefully, by day 5 or 6, the embryo will have expanded and started to protrude (or hatch) from this opening. The downside with starting a hole three days early is that you can’t control which part of the embryo leaves the zona first. If the techs are unlucky, the part hanging out will be the inner cell mass which is not the part to biopsy.

Another problem with waiting for hatching to biopsy  is that if you have a group of embryos, some will hatch on day 5, some will hatch on day 6 and some won’t hatch on either day 5 or day 6 in culture. Just because it hasn’t hatched on day 6 doesn’t mean it is dead. Why do I say that? Because every program has transferred unhatched day 6 blastocysts and have pregnancies to show for it but the pregnancy rate may be reduced. Our current culture systems do not support embryo growth beyond day 6 (and may even be suboptimal for day 6) so your embryo can’t stay in culture past day 6. It is also possible that spontaneous hatching  is not properly supported for all embryos on day 6 in  our current culture media even if the embryo is still viable. So because of limitations of the current culture system, embryos can’t stay in culture past day 6,  and have to be either frozen or discarded. If your clinic can’t or won’t biopsy an un-hatched embryo, it will be discarded unless you are okay with transferring a non-tested embryo. Why? Just logistics. If they can’t biopsy it , it can’t be tested and they probably won’t transfer an untested embryo, depending on what the genetic issue is. So using a clinic that requires spontaneous hatching in order to biopsy limits the patient’s options.

The alternative to waiting until the blastocyst spontaneously hatches is to make a hole in the zona and pull out the trophectoderm to biopsy the blastocyst on the first day on which it reaches the blastocyst stage. If the culture system is good, the majority of embryos reach blastocyst stage on the morning of day 5. If the embryo isn’t hatching on its own, the technician will have to have greater skill to make the hole and pull out part of the embryo for biopsy and not all programs offer this to their patients.

Another problem with waiting on spontaneous hatching in order to biopsy arises  for patients who were promised biopsy on day 5, overnight test results and a fresh embryo transfer the next day (day 6). This next day service invites disaster for patients but some clinics offer it because they think it is a marketing advantage to be able to offer a fresh transfer, even if it is using last-day-of-culture day 6 embryos. Programs with poor freezing programs also can avoid freezing the embryos by offering fresh transfer PGD. Even if the blastocysts cooperate by hatching on day 5, if the timing of spontaneous hatching is in the afternoon,  it’s still too late to get next day results because biopsy material usually needs to be shipped out of the IVF lab before noon on day 5.

Requiring spontaneous hatching to occur before biopsy also creates the possibility that not all of the embryos will be biopsied in time for next day results. If my patient has 10 embryos and only 5 are hatching in the morning on day 5, she will only get data from these 5 in time for a fresh transfer. If she is really unlucky, all her day 5 biopsied embryos will be abnormal and she won’t get a transfer. The fewer embryos she had to start with, the more likely she is to have no transfer. In any case, she won’t be able to select from all of her blasts, just those that hatched on day 5 and could be biopsied on day 5.

Overnight shipping for next-day results and transfer sounds great until a weather or aviation delay causes the samples to arrive late at the genetics lab.  There is not any leeway for delays of any kind, because some of the tests require 16 hours to run the genetic test, let alone check the results and issue a report. Add 8 hours transport time to get the sample to the genetics lab and you’ve used up all your time before you need to have a transfer or freeze everything.  I hate having to tell a tearful patient that because her embryo didn’t make the plane on time, we have to scrap the transfer and freeze the embryo anyway on day 6. The alternative would have required her to wait (and pay for a frozen embryo transfer) which is a con but the pro is that her healthier day 5 blastocyst would have been frozen and we could collect data on all her embryos, not just the ones that spontaneously hatched on our timetable, so she could have the best selection among her embryos for her eventual transfer.

So unless someone can provide compelling proof that waiting for hatching is essential to ensure the embryo is viable… (unlikely, because if that were true,  we’d never get pregnancies with unhatched day 6 blastocyst transfers–and we do) –it is problematic to wait for spontaneous hatching in order to do biopsy. Especially if your program is also selling you next day results. The better alternative is to biopsy expanded blastocysts on day 5 (or day 6 if they don’t reach blast stage until day 6), freeze all the biopsied blastocysts, ship the test cells and wait for the test results on all the patients. Sometimes fast McDonald’s style IVF isn’t  better.

 

© 2012, Fertility Lab Insider. All rights reserved.

©2012 Fertility Lab Insider. All Rights Reserved.

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