Pre-implantation genetics diagnosis (PGD) is a technique aimed at eliminating embryos created through in vitro fertilization (IVF), which have abnormal chromosomes or carrying serious genetic disease before pregnancy is established. Preimplantation genetic diagnosis (PGD) refers specifically to when one or both genetic parents has a known genetic abnormality and testing is performed on an embryo to determine if it also carries a genetic abnormality. These structural or numerical defects in the embryo can be seen more often in older pregnant women, especially those over 35. This situation may result in infertility because it reduces the chance of implantation and also causes unwanted miscarriages. As a matter of fact, 40 out of 100 pregnancies in women aged 39 and over will result in problems related to structural or numerical chromosomal defects. In contrast, preimplantation genetic screening (PGS) refers to techniques where embryos from presumed chromosomally normal genetic
parents are screened for aneuploidy.
Because only unaffected embryos are transferred to the uterus for implantation, preimplantation genetic testing provides an alternative to current post conception diagnostic procedures, which are frequently followed by the difficult decision of pregnancy termination if results are unfavorable. PGD and PGS are presently the only options available for avoiding a high risk of having a child affected with a genetic disease prior to implantation. It is an attractive means of preventing heritable genetic disease, thereby eliminating the dilemma of pregnancy termination following unfavorable prenatal diagnosis.
Indications for Preimplantation Genetic Screening
Most early pregnancy losses can be attributed to aneuploidy. Because only chromosomally normal embryos are transferred into the uterus, the risk of first and second trimester loss is markedly reduced. At present, no specific list of indications for preimplantation genetic screening (PGS) is available. For couples undergoing IVF, preimplantation genetic diagnosis may be recommended when:
1. One or both partners has a history of heritable genetic disorders.
2. One or both partners is a carrier of a chromosomal abnormality.
3. The mother is of advanced maternal age.
4. The mother has a history of recurrent miscarriages.
5. Couple had repeated IVF failures.
6. Male partner is facing problem of severe male factor infertility.
Thousands of clinical preimplantation genetic diagnosis cycles have been performed worldwide, resulting in the birth of hundreds of healthy babies.
The following are considered benefits or advantages of PGD:
The procedure is performed before implantation thus reducing the need for amniocentesis later in pregnancy.
The procedure is performed before implantation thus allowing the couple to decide if they wish to continue with the pregnancy.
The procedure enables couples to pursue biological children who might not have done so otherwise.
The procedure may help reduce the costs normally associated with birth defects.
In addition, hundreds of infants have been born following PGD/PGS worldwide. To date, there are no reports of increased fetal malformation rates or other identifiable
The main reason for opting this PGD procedure is that the risk of miscarriage during a normal pregnancy drops from 23 to 9 percent, the probability of the embryo
attaching to the womb nearly doubles, the chances of a clinical pregnancy and going home with a baby increase and the rate of multiple pregnancy decreases.
How is a PGD procedure performed?
Preimplantation genetic diagnosis (PGD) is a screening test used to determine if genetic or chromosomal disorders are present in embryos produced through in vitro
fertilization (IVF). Following are the steps involved in performing PGD procedure.
1. The patient’s suitability for PGD is evaluated by a doctor who specializes in the related disease.
2. Next, the couple is prepared for the IVF procedure.
3. The egg taken from the mother is fertilized with the father’s sperm in a laboratory environment.
4. Embryologists extract one or two blastomeric cells from the removed embryos via a biopsy.
5. Cells extracted via a biopsy are subjected to a special dyeing technique (FISH), which allows chromosomes to be examined under a microscope, following a
6. Embryos with structural or quantitative chromosomal defects are selected and removed. The healthy embryos are then transferred into the mother’s womb.