Genetic diagnosis

Doctor, is my baby okay?

This is a frequent question in the fertility consultation, as well as in the prenatal control, and it is our duty to inform about the different diagnostic techniques that exist for a correct evaluation, especially when it is increasingly frequent for pregnancies to reach older ages, where the risks of genetic alterations are increasing.

In general lines we could classify genetic diagnostic techniques into two groups: preimplantation and prenatal. Preimplantation refers to diagnosis before becoming pregnant and prenatal when the woman is already pregnant.

Preimplantation Genetic Diagnosis (PGD) is a complementary technique to In Vitro Fertilization (IVF) designed to detect chromosomal or genetic alterations before transferring the embryos to the woman’s uterus; that is, to carry out a genetic diagnosis before it is implanted. The specialized biologist performs a biopsy on the embryo and can study its chromosomes to detect alterations such as trisomies (for example, Down syndrome where there are three chromosomes 21 instead of two), monosomies or others; but alterations that involve a gene that determines a specific disease can also be studied.

In the preimplantation area we can also perform the karyotype or chromosome map of the parents if there is reason to suspect a problem in this regard. Then, in relation to the gametes that will give rise to future embryos, we can study the spermatozoa using the FISH technique.

The main causes for indicating PGD are:

  • History of repeated miscarriages.

  • Patients with translocations, inversions and other chromosomal abnormalities or monogenic diseases.

  • Repeated implantation failures in previous In Vitro Fertilization cycles.

  • Severe changes in seminal quality.

When we refer to Prenatal Diagnosis, we require genetic material from the current pregnancy, and in this sense there are two approaches: invasive and non-invasive.

In invasive tests we can perform chorionic villus biopsy between weeks 10 and 12 of gestation or amniocentesis from week 15. In both cases, the cells obtained are taken to be studied in the genetics laboratory to apply the most appropriate technique according to the case.

Among the non-invasive tests, ultrasound stands out between weeks 12 and 14, where ultrasound signs suggestive of chromosomal problems can be detected, where, if positive, amniocentesis is generally indicated.

This ultrasound can be accompanied by a blood sample to measure markers that also express the risk of chromosomopathies, and this is how we talk about genetic screening in the first trimester of pregnancy when we combine information from blood tests and ultrasound.

It has been discovered that the blood-placental barrier is not as perfect as we thought and genetic material from the fetus has been found circulating freely in maternal blood, which gave rise to a set of diagnostic tests where we can study the fetus from a blood sample from Mother. With this methodology we can know the fetal sex or if it is at risk of Down syndrome from week 9 of gestation.

“We can see that there are many alternatives to collect information and influence the diagnosis and prognosis of achieving a genetically healthy pregnancy; either alone or in combination, genetic diagnostic tests have been available for a long time and continue to evolving to offer better and more reliable results.”

Biol. Luis Machorro
Biol. Luis Machorro
Andrology Laboratory
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