Genetic testing during pregnancy

The number of women using the services of reproductive technology centers has increased significantly over the past twenty years. This is due to the fact that couples begin planning a pregnancy at a later age. Also expanded is the list of diagnoses in which pregnancy was impossible in the past, and now many couples may have children. In these cases, as a rule, in vitro fertilization (IVF) comes to their rescue.

Factors Affecting IVF Success

It would seem that with an increase in the number of IVF, the level of success of this procedure should increase significantly. However, as shown by the results of numerous studies on this topic, despite the popularity of IVF, improved diagnosis of infertility before this procedure, better equipment, better selection of drugs and a variety of protocols, the percentage of successful clinical pregnancies changed slightly and remains within 27–35% of cases The birth of living children for many years. It turned out that the success of the procedure depends little on the careful preparation of the endometrium, embryo transfer techniques and supportive hormone therapy, and is directly related only to the quality of the embryos. And the quality of embryos, in turn, depends on the age factor.

But since far from all married couples are able to have children at a younger age, the question of how to determine the quality of embryos, especially the presence of deviations in their chromosome set, is increasingly being raised. Also, the issue of the quality of embryos in relation to the presence of certain genes is raised by those couples who have a family history of diseases related to heredity, that is, the chromosomal genetic characteristic is especially important for them – the presence of genes or gene defects involved in the occurrence of serious diseases and malformations.

Until now, many hospitals prefer the traditional invasive procedure – chorion vortex intake to study the set of future child’s chromosomes (karyotype), which is usually carried out in early pregnancy. If deviations or altered genes are found in the karyotype, the woman may be asked to terminate the pregnancy. But what is the frustration of couples who spent large sums on IVF, got the desired result and faced with the dilemma of preserving a problematic pregnancy or its interruption due to a defect in chromosomes and genes!

In most publications on the topic of reproductive technology, there is evidence of a greater incidence of malformations in fetuses and newborns after IVF compared with the general population. but Recently, evidence has emerged that pre-implantation genetic testing not only lowers the number of pregnancies with fetuses affected by developmental defects, chromosomal and genetic diseases, but also increases the success rate of IVF and the birth of healthy children. This consolation is explained by the fact that such testing can eliminate defective embryos even before IVF. In fact, there is a selection of healthy embryos, the use of which will increase the chances of obtaining healthy offspring.

A lot of discussion has flared up around pre-implantation genetic testing in the recent past, especially in terms of the safety of this procedure for the embryo itself. Since this type of testing is expensive and requires both sophisticated technical equipment and specialists for its implementation and interpretation, the cost of IVF in general increases. This means that the frequency of abuse of this testing increases.

Types of pre-implantation testing

In modern reproductive medicine, there are two types of pre-implantation testing: pre-implantation genetic screening (PGS) and pre-implantation genetic diagnosis (PGD). In reality, there are no clear differences between the two types of testing, since they are carried out practically by the same methods, but the goals of their implementation are still different.

With an ASG, an (random) abnormal chromosome set is detected in embryos ready for replanting, and most often this type of testing is used when the age factor plays an important role. From 40 to 60% of all embryos in general are of poor quality, and with age the number of defective embryos increases, reaching 40% by the age of 40, which lowers the level of successful implantation after IVF to 6%. Therefore, pre-implantation genetic screening is increasingly used in couples over 35–37 years old, although there are no clear recommendations as to the age at which PGS should be conducted.

Unlike diagnostics, screening can be superficial, that is, it can be used to find out the total number of chromosomes and the absence of gross “breakdowns” in them.

PGD ​​allows to determine the presence of affected genes or changes in the chromosomes in the presence of genetic and chromosomal diseases in the genus or family. There are about 200 diseases associated with the breakdown of only one gene (cystic fibrosis, beta-thalassemia, myotonic dystrophy, Marfan syndrome, Duchenne muscular dystrophy, hemophilia A, etc.), including the occurrence of hereditary types of cancer (retinoblastoma, breast cancer, etc. .).

Also, such a diagnosis is important for determining the sex of the unborn child, since a number of hereditary diseases can be transmitted exclusively through the sex chromosomes.

Testing technology

There are several technologies for determining the karyotype and DNA, including those obtained from just one cell. All technologies have their advantages and disadvantages, so the results can be false-positive and false-negative, which requires the doctor to take into account many other important facts from the history of the married couple to make the right decision.

Material for research by biopsy can be obtained from a fertilized egg (8-14 hours after fertilization), and usually such testing is carried out in countries where the production of embryo cells is prohibited. This complex testing method also has many errors.

After fertilization, the egg begins to divide without increasing its size, which leads to the appearance of a blastomere: first 2 cells, then 4, 8 and 16 cells. When performing a biopsy, usually 1 cell is used at the stage of an 8-cell (3-day) embryo. In the past, two cells were taken for testing, but it turned out that the collection of ¼ (25%) of the cellular composition of the unborn child often had a negative effect on the development of the embryo. Loss of other cells was also observed (up to 33% of the embryonic cell composition). It takes from 1 to 2 days to get results, therefore, infusion is most often carried out on the 5–6th day of embryo development. This type of biopsy is accompanied by the worst level of embryo implantation – it decreases to 39%.

The blastomere division continues and certain parts of the ovum begin to form – this is how the morula appears, and behind it the blastocyst, which already contains a small amount of fluid inside, which allows for the collection of 5 to 10 embryonic cells. A larger number of cells for research improves the quality of diagnosis, therefore, this type of pre-implantation genetic testing is now being used more frequently.

As shown by clinical studies, PGS and PGD using a blastocyst do not negatively affect the development of the embryo, while at the same time improving the quality and success of IVF, although this type of testing increases the number of women who are not given IVF. If it is not possible to obtain high-quality and genetically healthy embryos, donor eggs, or spermatozoa, or ready-made embryos may be offered to the married couple.

Genetic testing during pregnancy

Unfortunately, far from all reproductive clinics conduct pre-implantation genetic testing. The quality of embryos in them is determined visually – taking into account the appearance (morphology) of the embryos. The use of pre-implantation genetic testing increases the success of implantation almost one and a half times compared with visual assessment.

Before conducting any kind of pre-implantation genetic testing, a married couple should be familiar with the pros and cons of this procedure and the IVF itself.

Of course, testing would be ideal, which allowed to determine not only the number and type of chromosomes, changes in individual genes, but also the entire genetic profile of the unborn child (a person has 20,000–25,000 genes responsible for the production of proteins, the value of other DNA segments not yet known). Modern technologies, including computer, allow you to create a map of the human genome (karyomapping), but this process is very expensive, so it is still at the experimental level. Bulk testing takes more time to get results. Therefore, even in reproductive clinics, PGS and PGD, due to their high cost and lack of time, are carried out in a shortened version (karyotype and / or genotation for 10–12 common diseases).

However reproductive medicine can no longer be imagined without pre-implantation genetic testing, and the rapid improvement of technology makes it possible to significantly improve the quality and safety of this procedure, allowing many married couples to have the desired healthy offspring.

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