9 Frequently Asked Questions about Preimplantation Genetic Diagnosis

What is Preimplantation Genetic Diagnosis?

Preimplantation genetic diagnosis (PGD) is considered the earliest form of prenatal diagnosis. It allows couples to avoid therapeutic abortion, a choice that can have devastating consequences, both clinically and psychologically. This procedure involves analyzing certain cells of an embryo to identify the embryo for transfer. This helps avoid transferring embryos that might be affected by very serious diseases, embryos that won't implant, or embryos that would result in children with serious chromosomal abnormalities.

What is the purpose of preimplantation genetic diagnosis?

Preimplantation genetic diagnosis primarily serves to:

• Reduce therapeutic pregnancy terminations. PGD allows for the transfer of embryos unaffected by the disease present in the family.
• Reduce miscarriages. With PGD, embryos that would lead to implantation failure or miscarriage are not transferred. In patients aged 40, the miscarriage rate is approximately 35%; with PGD, it is reduced to 8%.
• Increase the rate of full-term pregnancies per embryo transfer. If, through PGD, an embryo with normal chromosomes is identified and transferred, the pregnancy rate reaches 40%, regardless of the woman's age. This is because embryos with serious chromosomal abnormalities are not transferred.
• Minimize the rate of twin pregnancies. After chromosomal analysis, embryos that are chromosomally normal have a higher implantation rate, so they are transferred one at a time, significantly reducing the risk of a twin pregnancy. Multiple pregnancies represent a significant obstetrical and neonatal risk factor and are responsible for a 2- to 5-fold increase in complications during pregnancy and delivery.

Who is preimplantation genetic diagnosis indicated for?

Preimplantation genetic diagnosis is indicated when:

• There is a history of a very serious genetic disease in your family that can lead to significant disabilities or death in the first few years of your child's life.
• You have had several treatment cycles with negative transfers or miscarriages and you wish to minimize this risk.
• The woman is over 38 years old and you want to reduce the risk of miscarriage or transfer failure.

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What steps are involved in accessing preimplantation genetic diagnosis?

The first step is to find a specialized center that can guide the couple towards the most appropriate path, both genetically and gynecologically. Before embarking on PGD, it is essential to have a consultation with a geneticist and a gynecologist, to perform preliminary clinical tests, and then to undergo the Assisted Reproductive Technology (ART) treatment that precedes PGD.

Is preimplantation genetic diagnosis a safe technique?

Data reported in the international scientific literature show that biopsy of embryos on the 5th day of development (blastocyst stage) has no consequences on the viability of the blastocysts themselves. However, the embryologist must be an expert, because if the biopsy involves few cells (3 or less), it is likely that the biopsy cannot be read; if, on the contrary, the biopsy involves too many cells, this can lead to a decrease in the percentage of live births. The embryologist must therefore have specific skills and experience. The accuracy rate of PGD is very high, but there is a small possibility of error (1%). This is why prenatal diagnosis, chorionic villus sampling or amniocentesis, is always recommended to confirm the result of PGD.

What is the success rate?

If there are transferable embryos, the success rate varies depending on the type of PGD. It is important to remember that on average, it exceeds 40%. In addition, PGD for chromosome assessment reduces the negative effect linked to the woman's age during pregnancy.

What diseases can be prevented with preimplantation genetic diagnosis?

Several diseases can be prevented thanks to PGD. Hemophilia A and B, beta-thalassemia, Duchenne and Becker muscular dystrophy, cystic fibrosis, fragile X syndrome, spinal muscular atrophy, are just a few of the most frequent monogenic diseases that can be prevented by PGD.

What psychological impact can preimplantation genetic diagnosis have?

While selecting a healthy embryo and reducing the risk of abortion positively influences patient experience and reduces emotional stress, it is true that during the PGD process, the couple may experience difficult moments psychologically, due to the waiting time for the procedure and the fact that PGD does not guarantee success. In addition, there is a rate of error, however small, and the screening procedure does not guarantee that the embryo will implant or that the pregnancy will be carried to term. It is important not to have false illusions and to remain aware that these techniques are a valuable aid to conception but do not represent a certainty.

How to choose a good ART center for your preimplantation genetic diagnosis?

It is important that the ART center you choose has a good percentage of embryos that reach the blastocyst stage and that the embryos are collected on day 5/6/7.

It is important that the center has good experience in embryo vitrification and a high percentage of pregnancies resulting from transfers of previously cryopreserved embryos.

It is important that the center regularly performs biopsies - practice plays a crucial role. It is important to know the center's data, such as pregnancy and implantation rates of biopsied blastocysts.  

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