From what I’ve gathered, infertility treatment is a lot like high school: it’s highly hormonal, everyone’s in your business, and there’s nothing but test after test after test. I’d term it “Infertility High”, as goodness knows there are enough Infertility Lows.
I can’t help you with the hormones or with all the people up in your business (because technically, as a reproductive genetic counselor, I am one of those people). However, I can offer some help with the tests… Well, at least one of them: an explanation of possible results you see on Preimplantation Genetic Screening (PGS).
PGS is a genetic test designed to increase the success rates of IVF. Think of this article as PGS 102. For a crash course in the basics, please review PGS 101.
Jump ahead to your second semester. You’ve made it! You’ve undergone egg retrieval, fertilization, and the seemingly endless five day wait to see which embryos develop and can be tested. You’ve talked with your IVF doc, you’ve weighed the pros and cons of pursuing PGS, and you’ve decided to move forward with the test.
What type of results can you expect?
- Normal (a.k.a. euploid)
- Simply put, this is what everyone wants to see on their report card. This means that a given biopsy sample has the appropriate amount of chromosomal material, as far as PGS can detect. PGS is a highly advanced technology and has an accuracy rate of 97%, but it is important to know that PGS has limitations, which you should discuss with your doctor or genetic counselor. That being said, of the result options, this is the one you want.
- Aneuploid – This is the presence of an abnormal number of chromosomes in the cells of the biopsy sample, such as a whole extra or missing chromosome. Aneuploid embryos typically fail to implant or may result in a miscarriage. Some forms of aneuploidy, such as Down syndrome, which is caused by an extra copy of chromosome 21, can make it into a live birth; however, they are associated with developmental abnormalities.
- Partial/Segmental – This is when there is an extra or missing piece of a chromosome. So instead of an entire extra volume of a book, per say, there are extra or missing chapters. What this means for an embryo and its potential really depends on which specific chromosome pieces are extra or missing.
- Mosaicism – This is definitely the hot button topic of the day. To keep it brief, at the time of biopsy, five to six cells are removed from the trophectoderm (which is the part of the embryo that will develop into the supporting structures of the pregnancy like the placenta). A mosaic result occurs when some cells within the sample are found to have the normal amount of DNA (euploid) and some cells are found to be abnormal (aneuploid). Mosaicism is a complicated result finding because not as much research has been performed on these embryos and their likelihood of leading to healthy pregnancies and babies. From the research that has been performed, we’ve seen that mosaic embryos implant less and miscarry more than euploid embryos but can lead to healthy live births. Stay tuned for a future blog post that discusses this in detail.
- No Result (a.k.a degraded DNA)
- During the testing process, there is a 2% chance that amplifying (i.e., making more copies of the DNA within a biopsy sample) doesn’t work. In this case, a No Result is reported. It doesn’t mean the embryo’s DNA was normal and it does not mean it was abnormal. Simply put, the DNA wasn’t tested. There are many possible causes for this, including a poor-quality embryo. If you get a No Result, you can discuss the option of re-biopsying that embryo with your IVF physician. If you re-biopsy, there is a 50% chance of getting a result the second time around
Disclaimer: Please consider this the Cliff Notes version of possible PGS results. Just like you would never take your English final after skimming the Cliff Notes for Romeo and Juliet (you wouldn’t, would you?), you should never proceed with PGS without reading the entire play, or rather, having an in depth conversation with your IVF doc and a genetic counselor.