FAQ to Preimplantation Genetic Diagnos Performed (PGD)

Who would be benefited by PGD?

Couples with a history of recurrent miscarriage.
Women with history of repeated IVF failures
Family history of with genetic abnormality like beta thalassemai
previously affected child with genetic abnormailty like downs syndrome
known carriers of genetic defects like chromosome translocations.
women who have had to undergo repeated terminations because od an abnormality diagnosed prenatal.
couples morally and religiously opposed to termination of affected pregnancies diagnosed prenatal.

In couples with severe male factor infertility.


How is PGD diff from other prenatal diagnostic techniques?
There are various prenantal diagnostic techniques which presently help in the detection of certain genetic disorders in the fetus. These includes :
1- Chronic Villus biopsy (doen at 10-12 weeks of gestation)
2- Amniocentesis (done at 16-18 weeks if gestation)
Cordocentesis (done at 20-22 weeks of gestation)

The main genetic disorders tested include

1- cytogenetic anomalies i.e structural & numerical chromosomal abnormalities - diagnosed by karyotyping or FISH
2- Molecular genetic disrders i.e single gene disorders - diagnosed by PCR

As opposed to these prenetal diagnostic techniques, in PGD, the diagnostic techniques like FISH & PCR can be performed on the blastomere obtained from the embryo prior to implantaion. PGD thus helps to obviote the physical, emotional & psychological trauma assosiated with termination of pregnancy.

What is FISH?
FISH is molecular cytogenesis technique, which can be performed in non-dividing inter phase cells. FISH involves a chromosome specific fluorescently labeled DNA probes to hybridize to complementary genomic DNA. the signals are visualized using a fluorescene microscope. In case of normal diploid cell. tow signals are send for each chromosome. Presence of one signal for the chromosome being analyzed suggests monosomy and presence of three signals for the chromosome indicated trisome. FISH is rapid, reliable and useful genetic diagnostic test.

Which disorders can be diagnosed by FISH?
FISH can be used for

1- Detection of aneuploidies (numerical abnormalities)
2- Detection of translocations (structural abnormalities)
3- Sexing of the embryo (for x-linked disorders)



In PGD, which chromosomes are usually tested by FISH analysis?
the chromosomes most commonly tested include chromosomes 12, 18, 21, X & Y. The other chromosomes can be tested as and when indicated.

Incase of translocations in either of the parents specific to the patient need to be ordered.


What is PCR?
PCR is a powerful molecular diagnostic technique that allows in vitro amplification of a particular DNA fragmant, allowing generation of millions of copies in a short duration.


Which disorders can be diagnosed by PCR?
PCR is useful in the disgnosis of single gene disorders like beta thalassemia, cystic fibrosos, Ducchenne's muscular dystrophy, etc.

Can PGD be used for sex selection?
PGD can be used for proconception sex selection at the embryonic stage. according to the prenatal diagnostic techniques act, 1994, sexing of embryos is prohibited in India. However sexing of embryos can be performed for medical indications as in case of X linked disorders, where only female embtos (normal or carriers) may be tranfered.

What may be the problems encountered during performing PGD?
- Th case the embryo has started compacting, then it may be difficuilt to perform teh embryo biopsy.
- The cell may be lost during the procedure of embryo biopsy.
- The cell may be lost during fixation of cell on teh slide.
-The FISH signals may not be clear/ overlapping / split in some cases, making the diagnosis difficuilt.
- Mosaicism


Advantages of PGD?
- It is performed at the preimpantation state i.e befire the onset of pregnancy. PGD helps to increase the chances of having a normal baby.
- PGD helps to increase teh pregnancy rate and decrease the miscarriage rate.

How Preimplantation Genetic Diagnose (PGD) is done

How Preimplantation Genetic Diagnos Performed (PGD)


For PGD enbryos need to be generated in vitro. It must go through the ICSI procedure. The embryo are cultured in viro,byopsy is performed on the third day of fertilization and bad cells are removed from embryo. The biopsied cell is subjected to genetic diagnostic testes like FISH or Polymerase Chain Reaction (PCR). The results of genetic analysis are avialable in 12-36 Hrs. Once the results of the genetic analysis are obtained the enbryo which are normal are then trafsfred back to have the healthy baby.

Basic steps of the PGD are:

• Down Regulation
• Ovarian stimulation
• Oocyte Retrieval
• ICSI
• Embryo Culture
• Embryo Biopsy
• Genetic analysis (FISH or PCR)
• Embryo Transfer

How is embyo biopsy performed?

Cleavage stage embryo:
1- A hole drilled in the zona using laser or acid triodes
2- aspiration pipette broght close to the blastomere to be aspirated
3- the blastomere is aspirated with gentle suction
4- single blastomere with the nucleus clearly visible which is subjected to FISH or PCR.

What is Preimplantation Genetic Diagnose (PGD)

Many of couples have genetic disorder, and they have high risk of transmitting the genetic disorder to their offspring. Since now there was no technique to detect the same prior to the pregnancy being achieved. Preimplantation Genetic Diagnose (PGD) is new hope to detect the genetic disorder.


Preimplantation genetic testing is a technique used to identify genetic defects in embryos created through in vitro fertilization (IVF) before pregnancy. 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 see if it also carries a genetic abnormality. 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 (ie, amniocentesis or chorionic villus sampling), 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. It is an attractive means of preventing heritable genetic disease before implantation, thereby eliminating the dilemma of pregnancy termination following un-favorable prenatal diagnosis.


Primary candidates for PGD include the following:

• Couples with a family history of X-linked disorders (Couples with a family history of X-linked disease have a 25% risk of having an affected embryo [half of male embryos].)
• Couples with chromosome translocations, which can cause implantation failure, recurrent pregnancy loss, or mental or physical problems in offspring
• Carriers of autosomal recessive diseases (For carriers of autosomal recessive diseases, the risk an embryo may be affected is 25%.)
• Carriers of autosomal dominant diseases (For carriers of autosomal dominant disease, the risk an embryo may be affected is 50%.)