Preimplantation Genetic Screening and Testing
Most IVF programs recommend transferring 2 or more embryos during an IVF cycle. The reason is clear. Even in young healthy women, the majority of embryos are genetically abnormal, and abnormal embryos usually do not implant and those that do most often miscarry. Until recently, the only option was to put in multiple embryos to help tip the odds. Older methods of genetic testing such as FISH and day 3 PGS were simply unable to improve a couples chance of having a baby.
The development of new genetic technologies has changed that equation. We now can biopsy the embryos at the blastocyst stage, just before the embryo is ready to implant, so we get the most up-to-date genetic information. Even more important we can now screen for all 23 pairs of chromosomes at the same time. This procedure is often referred to as Comprehensive Chromosomal Screenining or CCS.
This is crucial information since most unsuccessful pregnancies (both natural and with IVF) are due to an embryo having one more chromosomes missing or containing extra copies. We call these embryos aneuploid and the object of PGS or CSS to identify them and avoid putting an abnormal embryo in. Putting in one genetically normal embryo yields very high pregnancy rates and very few multiples.
So, with all these advantages, why not do PGS / CSS with all IVF cycles?
- It is not inexpensive. The additional cost of doing this testing could help cover part of the cost the next cycle.
- Insurance will not cover the cost of it.
- PGS/CSS cycles lead to greater pregnancy rates per transfer, but not per cycle when you consider all the eggs that are retrieved in a given cycle, and each of those transfers.
- Since the embryos have to be grown to blastocyst stage, there is a chance that none of the embryos will be suitable for biopsy.
- There is a chance than none of the embryos testing will be genetically normal and not suitable for transfer.
- Embryos cannot be transferred back later than 6 days after the retrieval. Frequently, the embryos are not ready for biopsy until day 6, and the testing cannot be completed before day 7. That means the embryos are frozen and cannot be transferred back for another month. Many couples are unwilling to wait that long.