PGS identifies embryos that display chromosomal abnormalities that may result in IVF failure, miscarriage, or babies born with Down’s Syndrome or Edward’s Syndrome. It aims at improving pregnancy and lives birth rates by screening your embryos for chromosomal abnormalities and only implanting chromosomally normal embryos.
On the other hand, PGD provides information on whether or not a specific genetic disease affects an embryo. Families affected by any genetic disease should use this test to reduce the risk of their progeny carrying the genetic disease.
Some single gene disorders identified using the PGD technique are:
➥ Cystic Fibrosis
➥ Sickle Cell Disease
➥ Spinal Muscular Atrophy
➥ Huntington’s Disease
General steps followed in an IVF lab to proceed with PGS / PGD:
➥ Embryos are formed via In Vitro fertilization (IVF), supplemented by ICSI so as to avoid interference with paternal genes during screening
➥ Embryos are grown till Day 3 or Day 5
➥ Embryo biopsy is performed to remove cells from the embryo
➥ The biopsied cells are processed for PGS or PGD
➥ Based on the diagnosis, genetically healthy embryos are transferred into the patient.
Biopsy could be Either:(Day 3 / Blastomere Biopsy) : On day 3, the embryo comprises 6- 8 cells which are compactly arranged. The Blastomere biopsy removes 1-2 of the 8 cells for analysis. As cell size is comparatively large in comparison to day 5 blastocyst cells, it requires a large hole/laser hatching in the embryo shell to remove tightly attached cells. This may at times be traumatic for an embryo.
Day 5 / Trophoectoderm biopsy :
On day 5, embryos reach to blastocyst stage & comprise more than 100 cells. A biopsy can be done to remove 5-6 cells at this stage which gives much more accurate results of DNA analysis.
Also, a comparatively smaller portion of the embryo is removed from the outer layer of the embryo destined to form the placenta, called the trophectoderm (TE). The cells that form the baby are undisturbed, preserving the embryo’s true potential & thus is less traumatic for an embryo.
PGS and PGD are both advanced technologies in assisted reproduction and help to improve success rates in IVF procedures.