In the past, couples at risk of transmitting a serious genetic anomaly had no other option than amniocentesis to diagnose the health of their unborn child. Amniocentesis isn't risk-free, and it's done late in a pregnancy (in the second trimester), which makes it harder to decide whether to keep the pregnancy going or end it.
To avoid having to face this situation, many couples resort to a recent technique called preimplantation genetic diagnosis, or PGD.
PGD is a method in which embryos grown in a lab are tested for their genes before being put into the uterus of the mother.
Genetic testing can be used to find out if an embryo has the right number and types of chromosomes or if it has a specific genetic defect, like cystic fibrosis.
What does PGD do?
PGD is part of a process of medically assisted procreation (MAP) that requires the use of in vitro fertilization, with prior ovarian stimulation treatment. The couple must therefore meet the regulatory conditions for access to ART.
Several examinations are prescribed for the couple. The Pre-Implantation Diagnosis Center (CDPI) evaluates the genetic and gynecological feasibility, and the Multidisciplinary Prenatal Diagnosis Center (CPDPN) confirms the PGD indication.
After a technical development, the duration of which may vary depending on the indications, a multidisciplinary consultation (geneticist/genetic counsellor, gynecologist-obstetrician, biologist, psychologist, midwife, and anesthetist) is scheduled. The different stages of PGD and the results likely to be obtained are presented to the couple.
In practice, after ovarian stimulation, the collected oocytes are fertilized by intra-cytoplasmic sperm injection (IVF-ICSI). The biopsy of one to two blastomeres (embryonic cells) with a view to genetic analysis is generally carried out on the third day of culture. Only the pathology for which the couple presents a risk of transmission is sought.
PGD is a generally long process since it requires establishing a personalized procedure for each couple. The analysis techniques used are adapted to the pathologies: fluorescence in situ hybridization (FISH) for chromosomal abnormalities or molecular biology techniques for genetic diseases. Only disease-free embryos will be stored for transfer to the mother. In some situations, embryos may be frozen for later transfer.
The success rate of a pregnancy after PGD is equivalent to that of IVF, i.e., approximately 30%.
Preimplantation Diagnostic Phase
Before putting the embryo in the uterus after In Vitro Fertilization, the genetic material of the embryo is studied to look for changes in the genes.
A biopsy is performed on each embryo, and those with a concrete congenital disease are excluded.
One or two healthy embryos are transferred. Healthy embryos can be frozen.
Diagnosis can be obtained in two different ways.
Preimplantation Genetic Diagnosis with embryos
This study is conducted when the embryos are preferably at the blastocyst stage or have 6 to 8 cells, depending on the embryo's quality and quantity.A biopsy is performed on each of them in order to study their genetic material. Embryos that have a genetic disease are thrown out, and only healthy ones are chosen to go into the uterus.
Preimplantation Genetic Diagnosis with eggs
This technique makes it possible to detect genetic or chromosomal diseases in the egg before the embryo is formed. This technique only analyzes part of the ovum, namely the polar corpuscle, and makes it possible to detect hereditary pathologies on the mother's side. A biopsy is performed and, as soon as the polar corpuscle is extracted, the oocytes are inseminated using intracytoplasmic sperm microinjection (ICSI). After two days, the genetic result is known, and healthy oocytes are used to make healthy embryos.
How does preimplantation diagnosis (PGD) work during in vitro fertilization (IVF)?
Preimplantation genetic diagnosis (PGD) offers the possibility for a couple to have a child who will not be affected by a genetic disease that could be transmitted to them. So, PGD involves looking at the cells of embryos created through in vitro fertilization (IVF) before they even start to grow in the uterus.
This is done to rule out embryos that might have a disease that is caused by their genes or chromosomes. So, PGD involves looking at the cells of embryos created through in vitro fertilization (IVF) before they even start to grow in the uterus. This is done to rule out embryos that have a certain genetic or chromosomal disease.
As with conventional IV, we start with ovarian stimulation (by daily injections of hormones), which allows you to obtain more oocytes. They are then punctured and placed in contact with the spouse's sperm in a test tube.
It is only three days later that the pre-implantation diagnosis really takes place. The biologists take one or two cells from the embryos (with at least six cells), in search of the gene related to the disease sought. Then, IVF is continued: if one or two embryos are unharmed, they are transferred to the woman's uterus.
What distinguishes in vitro fertilization (IVF) from preimplantation diagnosis (PGD)?
Preimplantation diagnosis is carried out during in vitro fertilization, which makes it possible to ensure that the embryo, which is then implanted in the uterus, has not received the disease sought. If in vitro fertilization allows for a preimplantation genetic diagnosis (PGD) if necessary, then using IVF without a PGD is perfectly acceptable.This is especially true if you are having difficulty conceiving but do not have a hereditary, serious, or incurable pathology.
Preimplantation genetic diagnosis: what diseases are we looking for?
The appreciation is left to the doctors as to the diseases that are sought during the PGD. Moreover, there is still no diagnostic test on embryonic cells for all serious and incurable genetic diseases . It is therefore possible that a preimplantation diagnosis is not relevant even if you risk transmitting a pathology to your baby.
Genetic testing can be used to find out if an embryo has the right number and types of chromosomes or if it has a specific genetic defect, like cystic fibrosis. However, no exhaustive list has been defined.
Are there any examinations prior to the preimplantation diagnosis technique?
In general, the couple received genetic counseling before proceeding with PGD. He was then referred to the DPI centre. After a long interview and an in-depth clinical examination, the man and the woman must submit to a battery of tests , which are also long and restrictive. This is the same process that all people who want to use a method of medically assisted reproduction must go through, because PGD is not possible without in vitro fertilization.
What is Preimplantation Aneuploidy Screening (PGD-A)?
Preimplantation screening for aneuploidies, also called PGD-A, PGD-A, or PGS, looks at the number of chromosomes in the embryo to see if there are any problems. This increases the chance of getting pregnant after a transfer and lowers the risk of miscarriage.
Aneuploidy (abnormal number of chromosomes, e.g. trisomy 21) is a common cause of embryo implantation failures in utero. PGD-A is performed in addition to IVF in some infertile couples.
How does PGD or PGD-A take place?
This technique is performed at the blastocyst stage of the embryo, that is to say, between the 5th and 6th day of development, the main stages of which are as follows:
In vitro fertilization by ICSI
Extraction of a few cells from each embryo
In utero transfer of an embryo
Who is the PGD for?
PGD is mainly intended for couples with a known serious chromosomal (translocation, deletion, inversion) or genetic abnormality. Most of the time, the affection is shown when someone in the family has the disease or when the couple has already had a child with the disease.
Affections linked to the X chromosome
Autosomal dominant monogenic diseases
Recessive monogenic diseases
Structural chromosomal anomalies