Preimplantation Genetic Screening (PGS)

Preimplantation Genetic Screening, also known as Preimplantation Genetic Testing, is a diagnostic technique used for chromosomal profiling of embryos before implantation for an IVF treatment. The testing will be carried out for all 23 pairs of chromosomes present in the embryo’s cells. It can prevent embryo aneuploidy and is therefore called PGT-A. 

Why is PGS required? 

We know that when an egg (from a mother or female) gets fertilized by a sperm (from a father or male), the fertilized egg is known as an Embryo. PGS is required to check if an embryo has chromosomal abnormalities – monosomy (missing chromosome), extra chromosomes, chromosomal translocation, etc. 

Chromosomes are genetic material present in every cell DNA of human beings. Each cell would contain 23 pairs of chromosomes and a total of 46 chromosomes – 23 from the mother (or female) and 23 from the father (or male). Similarly, the embryo’s cells would have 46 chromosomes inherited from both parents. However, it is often found that not all embryos carry all 23 pairs of chromosomes, and some have – missing or an extra one or more chromosomes. An aneuploidy embryo mostly fails to implant on the uterine lining, causing failed implantation or early miscarriage during IVF treatment. 

But, with the help of PGS, we can profile the number of chromosomes present in the cells of embryos and evaluate whether they are healthy enough for implantation. Also, suppose an embryo with aneuploidy somehow gets implanted and leads to pregnancy. In that case, the baby(ies) born with this embryo has a high possibility of having genetic syndromes, e.g., Down syndrome. It can also affect maternal health. That’s why, in IVF, PGS is done to evaluate embryos for aneuploidy before transferring them inside the uterus for implantation. 

Who requires PGS? 

People who are getting an IVF treatment for infertility who have 

• Past unexplained miscarriages or recurrent miscarriages. 
• IVF implantation failure due to poor or aneuploidy embryos.
• Early miscarriage during IVF treatment.
• Women older than 35 years of age – because more than 75% of eggs from older women are abnormal, the percentage gets with age. If the egg is abnormal, then the embryo will also have abnormalities.
• Unknown cause of male or female infertility. 
• People who are opting for donor eggs, sperm, or embryos.
• To prevent multiple pregnancies – by transferring only one quality embryo (likely to get implanted) to the uterus instead of 2-3 embryos. 
• And if one or both parents are carriers of chromosomal defects even if they are healthy. 

In all the above cases, patients can get PGS for embryo profiling to get healthy embryos for embryo transfer.

The requirements for PGS will be evaluated from the patient’s medical profile by their fertility Doctor. 

PGS for IVF

IVF treatment is serving numerous infertile couples all over the world. Even people of different sexualities and genders seek IVF treatment to become parents. Furthermore, advanced IVF techniques like PGS and PGD can help people lower the risk of many complications, such as miscarriages and IVF implantation failure. It can also help parents with genetic disorders to have children without inheriting genetic defects. 

In IVF treatment, the harvested eggs and sperm (collected from the parents) are fertilized in the laboratory (in vitro) to develop the embryo, which will be inserted back into the uterus for implantation. It can take 5-6 days for embryos to grow to the blastocyst stage inside an incubator. After that, it is ready for transfer. But before the embryo transfer process, the embryos are profiled for chromosomal deformities because otherwise, it will affect the IVF process. 

Usually, many clinics assess embryos solely based on morphology. Nonetheless, It is observed that many IVF implantation failures and early miscarriages result from embryo aneuploidy. For this reason, PGT-A/PGS has become a crucial step of IVF treatment because it can inhibit IVF failure by only transferring quality embryos into the uterus for implantation. IVF center in Delhi takes every precaution to ensure the embryo’s quality before implantation.

Screening of Embryos

For the PGS test, once the embryos develop up to the blastocyst stage after 5-6 days of fertilization, the embryologist will select some quality embryos by morphology and standard screening. Then, a sample of 5-10 cells is collected from each embryo by biopsy with a precise laser and a microscope. These cells are collected from the ICM part of the blastocyst. The blastocyst embeds from the ICM part of the cell, which will grow into the placenta and, eventually, the fetus. It is not at all damaging to embryos to retrieve the cells, but it sure requires expertise. Finally, the cells will be forwarded for genetic evaluation by PGS at a genetic lab for 7-10 days. Meanwhile, the embryos will be kept frozen. 

At the Genetic laboratory, the embryos’ cells are analyzed for all 23 pairs of chromosomes (from both parents) with the latest technological innovations such as next-generation sequencing, array-based methods (aCGH), Single nucleotide polymorphism microarrays (SNP), etc. Array-based technology has improved PGT-A screening to a new standard where an embryo can be profiled for all 23 pairs of chromosomes instead of only 5 pairs (in the case of FISH). NGS also adds to the accuracy and reliability of the PGS with streamlined workflow and customizable assays for easy portfolio expansion. 

After receiving the PGC report of embryos, the healthiest embryo(s) is selected by embryologists for embryo transfer. 

Does PGS Help to Lower the Risk of Failed IVF and Miscarriages? 

Will it increase my IVF success rate?

PGS can surely increase the success rate of an IVF treatment from 40-50% to more than 70%. It also depends on the patient’s age, health condition, and cause of infertility. IVF implantation failure generally occurs due to abnormal embryo(s) and rarely due to uterine deformity. Also, (early) miscarriage results from embryo aneuploidy, where the body rejects the embryo. So, if a healthy normal embryo enters the uterus, it can be implanted easily and establish a pregnancy. Sometimes, assisted hatching is performed to help the embryo implant. 

Advantages of PGS for IVF at Risaa IVF

• Successful implantation and lower risk of miscarriage by 9-10%.
• Prevent multiple births.
• Embryo screening for all 23 pairs of chromosomes.
• Low risk of unhealthy children with a genetic syndrome such as down syndrome, Klinefelter syndrome, etc.
• Our Experienced fertility specialists and embryologists take interdisciplinary care of the PGS process. 
• Trusted and advanced genetic laboratory with the latest technologies like NCS, aCGH, SNP, etc. 

Are PGS and PGD the same?

Although almost similar, PGS and PGD are distinct and serve different purposes. PGS only reveals the number of chromosomes possessed by the embryos, whereas PGD is performed to identify specific genetic disorders if possessed by embryos. Check this out to know more about PGD.