Pre-implantation genetic diagnosis (PGD) is a method aimed at eliminating embryos created by in vitro fertilization (IVF) that have abnormal chromosomes or carry a serious genetic disease before pregnancy begins. Genetic diagnosis of preimplantation (PGD) refers specifically to when one or even both of the genetic parents have a known genetic abnormality, and testing is conducted at an early level to determine if it does not carry a genetic anomaly. These structural or numerical defects in embryos are more common in elderly pregnant women, especially those older than 35 years. This situation can lead to infertility, as it reduces the likelihood of implantation, and also causes unwanted miscarriages. In fact, 40 out of 100 pregnancies in women aged 39 and older will lead to problems associated with structural or numerical chromosomal defects. In contrast, genetic preimplantation screening (PGS) refers to methods in which embryos from suspected chromosomal-genetic parents are screened for aneuploidy.
Since only implanted embryos are transferred to the uterus for implantation, genetic testing of preimplantation is an alternative to diagnostic procedures for new diagnosis, which is often accompanied by a complex decision to terminate the pregnancy if the results are unfavorable. PGD and PGS are currently the only possible options to avoid the high risk of contracting a child with a genetic disease before implantation. This is an attractive remedy to prevent hereditary genetic disease, thereby eliminating the dilemma of ending pregnancy after an unfavorable prenatal diagnosis.
Indications for Preimplantation Genetic Screening
Most of the early loss of the pregnancy can be attributed to aneuploidy. Since only chromosomally normal embryos are transferred to the uterus, the risk of losing the first and second trimester is markedly reduced. There is currently no specific list of indications for genetic screening for preimplantation (PGS).
Thousands of clinical cycles of genetic diagnosis of preimplantation were performed around the world, resulting in the birth of hundreds of healthy children.
The advantages or benefits of PGD are listed below:
- The procedure is performed before implantation, thus reducing the need for amniocentesis later during pregnancy.
- The procedure is performed before implantation, which allows couples to decide if they want to continue the pregnancy.
- This procedure allows couples to pursue biological children who might not have done it otherwise.
- This procedure can help reduce costs, usually associated with congenital disabilities.
Also, hundreds of babies were born after PGD / PGS around the world. To date, there are no reports of an increase in the frequency of fetal development or other identifiable problems.
The main reason for choosing this PGD procedure is that the risk of miscarriage during normal pregnancy decreases from 23 to 9 percent, the probability that an embryo attached to the uterus almost doubles, the chances of a clinical pregnancy and returning home with an increase in the baby and the frequency of the multiple pregnancy decreases.
How is the PGD Procedure Performed?
Preimplantation genetic diagnosis (PGD) is a screening test used to determine the presence of genetic or chromosomal disorders in embryos obtained by in vitro fertilization (IVF). The following are steps related to the implementation of the PGD procedure.
1. The patient’s suitability for PGD is evaluated by a doctor who specializes in the related disease.
2. The couple is then prepared for the IVF procedure.
3. The egg taken from the mother is impregnated with the father’s sperm in the laboratory environment.
4. Embryologists extract one or two blastomere cells from the removed embryos by biopsy.
5. Cells extracted with biopsy are subjected to a special staining technique (FISH), which allows you to examine the chromosomes under a microscope after the fixation process.
6. Embryos with structural or quantitative chromosomal defects are selected and removed. Then, healthy embryos are transferred to the mother’s uterus.
Although PGS was included in the treatment of patients undergoing IVF treatment, its indications, usefulness, and results remain an active area of research in the field of reproductive medicine. As preimplantation is optimized for medical disorders at the early level, its place in medicine and society will continue to cause controversy and ethical debate.
Despite all its advantages, the cases in which this method will be used should be carefully selected. It should be remembered that the PGD procedure requires that the cell is removed from the embryo by biopsy. Thus, there is a chance to harm the embryo, and this procedure has a 10 percent error. Thus, it is believed that it causes more harm than good when it is performed unnecessarily.