Preimplantation Genetic Diagnosis (PGD)
Preimplantation Genetic Diagnosis is an integrated part of IVF treatment. It is performed alongside PGS for an IVF treatment where one or both parents have a genetic disorder. Preimplantation genetic diagnosis is carried out for testing an embryo or cell for a single gene disorder or mutation. Unlike PGS, PGD is not required for every IVF case.
Difference Between PGD and PGS
PGS: In preimplantation genetic screening, the embryos are examined for the number of chromosomes acquired by them and the position of chromosomes. In total, a healthy embryo will have 46 chromosomes. Any embryo with fewer or more chromosomes is considered abnormal and will not implant after transferring to the uterus – during IVF treatment. PGS doesn’t determine the specific genetic disorder in embryos, if any.
It can increase the likelihood of implantation of embryos after the transfer and decrease the risk of early miscarriage. PGS will also prohibit IVF children from having chromosomal anomalies like down syndrome.
PGD: In preimplantation genetic diagnosis (also known as single-gene PGD), the cells of embryos aren’t diagnosed for the number of chromosomes but rather for single-gene disorders. Single gene disorder occurs due to mutation or change in the DNA pattern of a specific gene. Following the PGD, the children of parents with any genetic disorder can be excluded from genetic disorders after an IVF treatment.
PGD is only performed in specific cases, and it is performed with PGS, and never alone.
Why is PGD required?
Suppose one of the parents has genetic diseases or single gene disorders, viz. Cystic fibrosis, sickle cell anemia, spinal muscular atrophy, Tay-Sachs, Fragile X, etc., their children have a 50% chance of inheriting the disorder or disease from the parent. Even if the parent is healthy but has genetic and chromosomal abnormalities in their genes, their gametes (egg and sperm) might carry these genetics to their children, risking them for genetic diseases.
People who have genetic diseases or abnormalities and are fertile can conceive naturally, but their children might also carry defective genes. Even if they find out that their child has a single gene disorder during fetal development, abortion is not an easy option for many parents.
But, With the help of IVF and PGD, couples or parents with genetic anomalies can strategically plan a pregnancy and give birth to a healthy child. They wouldn’t have to make tough decisions over the life of their unborn child, but rather they can choose a genetically healthy embryo for IVF treatment. That’s why even fertile couples with genetic abnormalities choose IVF treatment with PGD to have a healthy baby.
Who Requires PGD?
Generally, PGD is not necessarily required for screening embryos, and PGS is enough. However, if the biological parents already have a single gene disorder, then PGD is suggested with PGS for IVF treatment. Here ate some situations where PGD is the best suitable option:
- One or both parents suffers from genetic diseases, e.g., Cystic fibrosis, B-thalassemia, sickle cell disease and spinal muscular atrophy type 1, Myotonic dystrophy, Huntington’s disease, Charcot-Marie-Tooth disease type 1A, Down syndrome, reciprocal translocations, Human leukocyte antigen (HLA) matching.
- Parents are healthy, but one or both are carriers of defective genes or have a chromosomal translocation.
- Parents already have a firstborn with a genetic disease or carry a genetic abnormality.
- Unknown cause of female and male infertility.
- Women who are older than 40 years of age and want to have IVF treatment.
PGD for IVF Treatment
PGD for IVF follows the same procedure as the standard IVF procedure. The eggs and sperm samples are retrieved from the parents and fertilized artificially by assisted insemination in an ideal culture inside an incubator. The fertilized eggs are kept inside the incubator to evolve into multicellular embryos (blastocyst) in 5-6 days.
The potential embryos are selected morphologically. Embryo biopsies are conducted to collect 5-10 cells from each embryo. These cells will be sent to the genetic lab for PGS and PGD (only in the special cases mentioned above).
At the genetic lab, PGD is performed for a single cell of an embryo for a particular genetic mutation. It can detect any mutation of DNA patterns in cell genes and chromosomal translocation. Modern technologies like Polymerase Chain Reaction (PCR), array-based methods, Single-Cell Genome Sequencing, etc., are used for PGD.
With PGD, embryos free from any genetic and chromosomal defect can be specified for IVF treatment. We can see if an embryo has any single gene disease or if it carries a disorder that can pass down to the child. For this reason, both PGD and PGS are crucial to have a healthy baby and a healthy pregnancy.
Is there any risk of PGD?
Even though there is no risk of PGD, it can be a bit unreliable because it is evaluated for only a single gene of a cell. Also, cell biopsy and chromosomal mosaicism may or may not affect embryos if precautions are not taken. And children with genetic disorders may be born even after PGD.
Does PGD increase the success rate of IVF?
Not necessarily, PGD can increase the fate of having a healthy child, but this single factor can’t determine the IVF success rate. Yes, it can lower the risk of implantation failure and (early) miscarriage, but live birth is still not vowed.
Note: PGD/PGS can also be used for having a child of a particular sex, but this process is illegal and not welcomed in India.
PGD/PGS at Risaa IVF
We have collaborated with the best Genetic laboratory and have an experienced team who distinctively takes care of PGD/PGS for special IVF cases. Our team follows all the protocols to ensure that only genetically healthy embryos are used for IVF treatment. Any parent want-to-be with genetic defects can have a healthy child of their own with the help of the right team, just like us.