What is preimplantation genetic screening (PGS)?
Preimplantation genetic screening is also known as embryo screening, preimplantation genetic diagnosis, and aneuploidy screening. It is a procedure that can be applied to embryos created through IVF and ICSI (Intracytoplasmic Sperm Injection) to screen for abnormalities. Preimplantation genetic screening can look for many conditions that are caused by a single gene, as well as for chromosomal abnormalities.
PGS can screen for cystic fibrosis, Tay-Sachs, sickle cell anemia, and Huntingdon disease. In addition, recessive and dominant sex-linked disorders like fragile X syndrome and vitamin D resistant rickets can be looked for with PGS. Preimplantation genetic screening is a screening procedure rather than a diagnostic procedure. Although it aims to prevent the implantation of embryos that are deemed to have a higher risk of carrying the abnormalities that are screened for, it is not something that eliminates the possibility of having a child with a genetic condition. Preimplantation genetic screening is also used to identify the strongest and healthiest embryos created through IVF, and can also be used to "profile" an embryo to match a sibling so that the embryo can become a bone marrow donor later on, in other words, to create a "savior sibling".
Who should participate in preimplantation genetic screening?
Preimplantation genetic screening is recommended for couples who have a family history of genetic conditions. It's also suitable for people who already had a child or children with a genetic condition the preimplantation genetic screening procedure can screen for. Women who have had several miscarriages, or who are using IVF to get pregnant after 35 may also talk to their medical team about PGS. Couples who have experienced several unsuccessful cycles of IVF should consider the procedure too, as failed IVF attempts can be due to chromosomal problems in the embryos. The advantages of preimplantation genetic screening vs screening and diagnostic tools used later on in pregnancy are clear. PGS may allow couples who have been affected by genetic conditions to have biological children, something they may not have felt comfortable with otherwise. For those who would want to terminate a pregnancy in case the baby was affected by a genetic disorder, preimplantation embryo screening eliminates a long wait and a lot of stress. There are ethical concerns about the procedure too, of course preimplantation genetic screening is certainly a manifestation of what some people refer to as "playing God". With embryo screening, medical professionals decide which embryo is given the chance to implant, and which isn't. At the same time, the screening process doesn't completely rule out the chance that the future child will have a genetic disease, so it may offer a false sense of security. On the other hand, many people who do carry genetic disorders live happy and functional lives and may not even have symptoms until much later in life.
PGS the procedure
Preimplantation genetic screening is carried out as part of your IVF or ICSI procedure. There will be an additional fee, of course. PGS takes place after your eggs have been fertilized, on day two or three. The blastocyst (future embryo) will have eight cells at that point, and one or two cells are removed. After an embryologists removes these cells, the number of chromosomes present in them can be tested, and they can be examined for any other abnormalities. This procedure is carried out on all of your embryos, so that the best embryos to implant can be identified. Embryos that are found to be affected by genetic conditions may be destroyed or can be used for scientific research where consent has been given.
The procedure can also be carried out on days five or six, in which case more cells can be removed for testing. Some embryologists believe this to lead to more accurate results. So, what are the risks of preimplantation genetic screening? The removal of cells from a fertilized egg may seem like a rather invasive procedure. Most of the time, PGS doesn't damage the blastocyst in a way that can be observed. In some cases, the fertilized egg is damaged to the point that it can not be used for IVF anymore, though. Then, there's the possibility that all of the tested blastocysts are found to have a genetic problem, leaving none to implant.