Preimplantation Genetic Diagnosis, or PGD, is a genetic diagnosis method used in certain In vitro Fertilization (IVF) treatments. It is normally done to diagnose the presence of genetic disorders in the embryo before its implantation. When the couples undergoing IVF have a history of genetic disorders, PGD is recommended. PGD also helps in analyzing the reason for frequent miscarriages in a woman.
Advantages of Using PGD
PGD can be used to diagnose the genetic disorders caused by a single chromosome or a gene. With PGD, various genetic disorders can be detected and defective embryo implantation can be prevented so that you will not conceive a fetus with genetic disorders.
- Most commonly diagnosed genetic disorders through this method are hemoglobin disorders and cystic fibrosis.
- In couples having a history of Beta Thalassemia, PGD can be done to separate the unaffected embryos and implant only them.
- Aneuploidy means a condition where there is abnormal number of chromosomes due to the presence or absence of a chromosome. Aneuploidy can be caused by age, and it can be correlated to higher rate of implantation failure or miscarriages. Hence, in couples having IVF treatment at an advanced maternal age (AMA), PGD can be done to diagnose the presence of aneuploidy so that the implantation of a genetically defective embryo can be avoided.
Limitations of PGD
PGD cannot be done to analyze the presence of every chromosome and also some abnormalities of chromosome or rearrangement of chromosomes. Misdiagnoses in PGD can occur due to mosaicism in the cells of the embryo or due to clinical laboratory errors. Certain scientists have a strong notion against PGD, as removing blastomeres from the embryo for genetic analysis can lead to side effects to the embryo, resulting in birth defects.
Trophectoderm biopsy is a treatment similar to that of PGD. Here, the genetic screening is done in 5- to 6-day-old embryos instead of 2- to 3–day-old ones (in PGD). At this stage, the embryo would have separately allocated cells for the development of the fetus and placenta (trophectoderm). In this technique, more cells from the trophectoderm are removed and used for genetic screening. Thus, the possibility of damage to embryos by cell removal can be overcome in this procedure. As more cells are tested in this method in contrast to that in PGD, the results of the test will be more accurate than that of the PGD.
Prenatal diagnosis is one of the most reliable methods of screening for genetic disorders. Generally, embryos of poor quality fail to implant themselves; hence, instead of conducting PGD before implantation, prenatal diagnosis can be performed after pregnancy. Various techniques of diagnosis like aminocentesis, chorionic villus sampling, fetal blood cells in maternal blood, maternal serum estriol and ultrasonography are available for accurately diagnosing the genetic disorders in the fetus. As the results of these tests are reliable, decisions regarding the abortion of the fetus or completing the gestational period can be taken by the couples after consulting their physician.