Screening and preimplantation diagnosis in IVF
Preimplantation genetic screening (PGD) is a laboratory technique for identifying embryos with chromosomal abnormalities.
Screening and preimplantation diagnosis in IVF
Preimplantation genetic screening (PGD) is a laboratory technique for identifying embryos with chromosomal abnormalities.
Screening and preimplantation diagnosis in IVF
Preimplantation genetic screening (PGD) is a laboratory technique for identifying embryos with chromosomal abnormalities. The goal is to transfer only healthy embryos, conceived in vitro, into the patient's uterus.
PGD can be offered to:
- To patients of advanced age
- Couples with a history of repeated implantation failures
- Couples with a history of repeated unexplained miscarriages
- In cases of severe male infertility
- To perform PGD, Clinics performs a biopsy of the embryo's trophectoderm.
This allows to recover a few cells from each blastocyst (5-day-old embryo) in order to analyze them. This technique is also used to screen the sex of the baby for couples who want to choose the sex.
Blastocyst biopsy
The cell samples are then sent to a specialized laboratory. Within a few days, the results on the chromosomal status of the blastocysts are known. It is then possible to select a healthy embryo and proceed with its subsequent transfer into the patient's uterus.
The use of PGS
PGS is an authorized practice in some foreign centers. It is used when patients are elderly, but it can also be offered to them as early as age 35 in some facilities. Specialists and couples can also resort to this procedure when couples encounter several implantation failures, notably due to an excessive number of aneuploid embryos.
It is possible to combine PGS with an IVF (in vitro fertilization) attempt. In the United States, this screening is usually offered to couples making their first IVF attempt, without waiting for initial results. This is a point that contributes to the debate around this practice.
The difference between PGD and PGS
Biopsies performed in the context of PGD and PGS do not have the same objectives. Preimplantation diagnosis, or PGD, seeks to detect signs of a possibly hereditary or recurrent disease in the couple's family. The goal is to avoid transmitting the disease in question to the child and to avoid possible suffering. This makes it possible to exclude affected embryos from uterine transfer.
The PGS does not have the same objectives. It is a screening technique, not a diagnostic one. Therefore, it consists in searching for embryos without any chromosomal abnormalities and selecting the "best candidate" for implantation.
It is possible to choose what is described as the "best embryo" according to morphological and morphokinetic criteria. The latter are elements constituting the morphology and associated with the speed of development of the embryo. With this technique, the principle of selection remains limited: no information on the chromosomal content of the embryo is revealed. Thus, the sole purpose of this type of examination is to favour the start of a pregnancy desired by a couple without basing it on the characteristics of the child.
The debate of sex/gender selection
Preimplantation genetic screening aims at selecting chromosomal or genetic criteria in the child. This type of practice can lead to abuses: researchers use this technique to analyze the genes of embryos and to know, for example, the sex or the color of the eyes of the child to be born.
Therefore, an ethical question is now feeding a debate related to this possible selection of criteria and the human intervention that accompanies it. Being able to choose the characteristics of children is not a new concept, but it raises moral questions. Thus, this practice divides the international scientific community, as well as the legislators. It is for this reason that it remains prohibited in Canada and France. But it is authorized in some other countries such as Mexico, the United States, Italy, the United Kingdom, Malta, Cyprus, Romania, Slovakia, Spain and Luxembourg.
On the other hand, a study conducted in the United States shows that PGS does not bring any real improvement in birth outcomes for women under 37 years of age. For older women, it turns out that it may be necessary to wait several cycles to finally have an embryo implanted. This is due to the large number of embryos with abnormalities related to the advanced age of the patients.
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