Within the niche of Assisted Reproduction Techniques like In Vitro Fertilization (IVF), pre-conceptual genetic testing in the form of preimplantation genetic screening (PGS) is a common practice. This testing is aimed at detecting embryos that present a greater risk of not being able to survive the IVF procedure. This is why preimplantation genetic screening is also called Embryo Screening.
Please note that both PGD and PGS refer to pre-pregnancy embryonic testing and serve a similar purpose—help in identifying healthy embryos to raise the chances of a successful and healthy pregnancy. However, there is a basic difference between the two.
Preimplantation genetic diagnosis is recommended when either or both of the genetic parents carry genes indicating a genetic disorder. Here, the embryos are tested to check whether genetic abnormalities have been transmitted from the parents to the embryo. Preimplantation genetic screening is recommended even if the parents don't present a personal or family history of genetic disorders; in other words, it is not aimed at decoding specific diseases. Preimplantation genetic screening is aimed at testing each embryo for its overall health to ensure that it is worthy of being used for implantation during an IVF treatment.
Preimplantation Genetic Screening and Aneuploidy
PGS is particularly recommended for identifying a typical kind of chromosomal abnormality, called aneuploidy. This refers to a condition wherein the number of chromosomes in the embryo are either too few or much more than the normal. In either scenario, an aneuploid child has a high propensity to develop genetic disorders like Trisomy 18 (Edwards Syndrome). Further, aneuploid embryos are likely to cause failed pregnancies. PGS is largely regarded as being quite efficient in decoding aneuploidies in embryos using advanced testing methods such as FISH (Fluorescence in situ hybridization). Common aneuploidies that are identified through PGS include aneuploidy of chromosomes 13, 16, 18 and 21.
Repeated Miscarriages and Recurrent Pregnancy Loss
Chromosomal abnormalities are responsible for early loss of pregnancy, such as during the first and second trimester. Using PGS, the fertility clinic can help patients who had been suffering from various forms of pregnancy loss, like Repeated Miscarriages (RM) or Recurrent Pregnancy Loss (RPL). Once PGS reports confirm the presence of aneuploidies in an embryo, it is not used for implantation, directly raising the chances of establishing a pregnancy with the chosen healthier embryos.
Repeated IVF Failures
Couples with a history of repeated IVF implantation failures or RIF benefit tremendously from PGS. RIF is established when a couple cannot conceive even after attempting three embryonic transplantations. Such a high failure rate denotes a problem within the embryo itself, an aneuploidy.
Women of Advanced Maternal Age
Women with Advanced Maternal Age, or AMA, present a major deterrent to a successful IVF procedure. In fact, most statistics indicate that the chances of chromosomal abnormalities steadily rise as the female ages. For women who are above the age of 40, the risk of failed IVF pregnancy is even higher.
Genetic Disorders Induced by Male Factor Infertility
Men suffering from severe infertility in the form of having an extremely low sperm count or motility present a greater likelihood of inducing genetic abnormalities in the embryo. Examples of such genetic disorders include:
- Klinefelter syndrome
- Robertsonian translocations
- Cystic Fibrosis
- Androgen Receptor Mutations