Chapter 4 - Results and Risks


You’re watching Results and Risks, chapter four of the genetics and fertility video series from the American Society for Reproductive Medicine.  

The preimplantation biopsy procedure itself doesn’t introduce any genetic errors. Most embryos are biopsied about 5 to 6 days of development.  By this time, the cells can be taken from the outer layer that will become the placenta.  The embryo may be frozen at this point to allow time for the testing.

It’s reassuring to know that, for the most part, a few cells can be removed safely from an embryo. In fact, embryos also lose cells in other situations, like when an embryo splits into identical twins. Sometimes cells are lost during the freeze and thaw of a frozen embryo but a healthy baby is born. Though no procedure, including biopsy, is completely risk-free, the benefit of the information gained can balance that risk. Sometimes, embryos stop dividing after biopsy, but it’s hard to know if this is because of the procedure or if it would have happened anyway.

Other risks to the embryo are small. For instance, though the embryo stays at your original lab, the biopsied cells are often sent to a different lab for testing. There is a chance that those cells could be lost or damaged in transit to the testing facility. There’s also the possibility that the sample could be contaminated. Laboratories have protocols and safeguards to minimize the risks. Another risk is that in testing only a few cells from the part of the embryo that becomes the placenta, there is a small chance that they don’t represent the rest of the cells in the embryo.

We can’t test every cell and then still transfer the embryo, so this may be the best test available to help choose the best embryo for transfer. This is why we still recommend considering genetic testing during pregnancy. There is a small chance that results from your embryo's testing may be different than results obtained during pregnancy, even after transfer of a tested embryo.

Also, we don’t think that removing those few cells damages the embryo, but it is possible to cause harm to the embryo or have an effect that we don’t yet understand. So far, children born from this process seem healthy.  Even with PGT, other testing during pregnancy could reveal genetic issues unrelated to what was screened for with PGT.

It’s possible, though not likely, to discard an embryo that tested abnormal but was truly normal, or transfer an embryo that tested normal but was truly abnormal. Also the significance of some test results are not well understood. There is still much that science can’t explain about this process.

It can be disappointing if your cycle results in no normal embryos to transfer.  But this could be helpful information.  You can try another cycle to identify a normal embryo sooner than if untested embryos were transferred that resulted in miscarriages or negative pregnancy tests.

We hope you found this information helpful. For the next chapter in this series please click here.

For more information about genetic testing in the setting of infertility treatment please visit
is a patient education website of ASRM.