What is Preimplantation Genetic Diagnosis?
Preimplantation Genetic Diagnosis (PGD) is a prenatal method used for genetic diagnosis in early embryos before they are transferred to the woman’s uterus. It consists of performing a genetic exam on biopsied embryo cells in order to determine possible chromosomal or gene alterations. Following the exam, only the healthy embryos are chosen for transfer to the woman’s uterus.
With women or couples who are at risk of passing down chromosomal or genetic alterations to their offspring, a PGD can alert us about the state of each single embryo, thus allowing us to choose only those embryos deemed healthy enough for uterine transfer.
PGD is a complex process and cannot be performed for every single disease. The law regulates which diseases and conditions are allowed to be screened for, as well as which ones are not. Some conditions and diseases require us to request special permission from the National Commission of Assisted Human Reproduction (Spain) which will then determine whether or not the PGD treatment can be performed.
When is Preimplantation Genetic Diagnosis Recommended?
PGD is recommended when the embryos are at risk for serious alterations in the number or structure of chromosomes. It is also recommended when there is a chance of a gene alteration which could be the cause of an inherited genetic disease. At the same time, PGD is recommended when there are serious doubts about the viability of the embryos based on family history.
The Preimplantation Genetic Diagnosis Procedure
PHASE I: PRELIMINARY INFORMATION
In this phase we will perform a genetic screening in order to screen for the diseases that could be passed down from the parents. Here we strive to gather as much information as possible prior to starting the PGD.
PHASE II: OBTAINING THE EMBRYOS
Although the parents may not have any kind of problems conceiving, the embryos will be obtained by means of an In Vitro Fertilization treatment.
PHASE III: EMBRYO BIOPSY AND GENETIC ANALYSIS
The embryo biopsy will be performed three days after fertilization has been confirmed, meaning that the embryo will be in a state of between six and eight cells. The biopsy involves extracting one or two cells from the embryo. This step does not disrupt the embryo’s normal development. Once the biopsy is complete, the embryo will be returned to the incubator where it will be kept in a culture until the results of the test are received and the embryo’s possible transfer has been evaluated.
The biopsy that has been obtained will be sent to a Genetics Reference Laboratory where it will be processed using Array CGH or PCR techniques. We will receive an analysis and diagnosis of each embryo that was biopsied.
PHASE IV: EMBRYO TRANSFER
Once we have received the results of the genetic analysis we will decide which embryos are going to be transferred based on their chromosomal make-up and characteristics of embryo viability.