Reproductive genetics
Genetics and its relationship with fertility
It is estimated that 25% of women will suffer a miscarriage in their lifetime. Behind 50% of these spontaneous miscarriages there is some type of chromosomal abnormality. These anomalies can often be related to advanced maternal age.
On the other hand, there is a high number of genetic diseases; it is estimated that 6-8% of births will suffer from one. Since the 1980s, rare diseases have been acquiring a priority place in health programs and in public opinion. They are defined as those that have a prevalence of less than 12,000 individuals. In general, they are chronic, disabling diseases and more than 80% of genetic origin. It is estimated that there are between 7,000 and 8,000 rare diseases that affect the Colombian population.
Both scenarios represent a great challenge for assisted reproduction. Detecting these alterations in time allows us to achieve high rates of healthy newborns at home.
Genetic testing in pregnancy planning
CONSTITUTIONAL KARYOTYPE
This is a test also known as a fertility karyotype test, which is part of the routine analyses and basic fertility tests for both members of the couple. Through a blood sample from the patient, the set of chromosomes of a person is examined and information is reported about possible anomalies that they may have (translocations or inversions) which do not cause any symptoms in the patient.
However, if one of the parents is a carrier of an anomaly in their karyotype, it may be causing the formation of chromosomally altered embryos, which can lead to implantation failures, spontaneous abortions or even diseases compatible with life.
SPERM FISH
It is a cytogenetic technique that is performed on the semen sample to analyze the chromosomes of the male gametes. It is indicated in the study of male infertility. One of the drawbacks of this test is that it analyses a sample that will not be useful, so it is an approximation and not a diagnosis as such.
CARRIER TESTING, GENETIC COMPATIBILITY TEST OR CARRIER TESTING
This is a test that allows the transmission of genetic diseases, recessive inheritance or linked to the X chromosome, to be minimised to the offspring. This test is capable of identifying mutations in the genes of the reproductive couple, and detecting whether or not there are matches.
Carriers of mutations in any of these genes have a normal copy of the gene that dominates over the mutated copy, therefore, they do not present symptoms. The risk appears when both members of the couple have mutations in the same gene. In this case, the probability of having an affected child is 25% in each pregnancy.
It is indicated in the following cases:
In any couple with a desire to reproduce who has or does not have a history of genetic diseases in their family.
In consanguineous couples, since it is much more likely to share mutations in the same gene.
In couples who go to assisted reproduction clinics and are going to undergo an in vitro fertilization process, both in a treatment with their own gametes, as well as with donated gametes.
After the study, a comparison of the results of the genetic parents is required to determine the suitability or “genetic compatibility”.
In the case of a treatment with gamete donation, a donor will be assigned who is negative for genes with mutations present in the recipient.
In the case of couples with their own gametes who do have mutations in the same gene, they will be informed of the reproductive options to avoid the transmission of the disease:
Preimplantation genetic testing in embryos obtained by in vitro fertilization.
Change of gamete(s) in one of the two parents.
Adoption.
Genetic testing in the preimplantation stage of the embryo or preimplantation
PGT or preimplantation genetic testing (PGT) is the study carried out on embryos generated using in vitro fertilisation techniques, which allows us to know if they are affected by any chromosomal or genetic alteration before being transferred to the mother’s uterus. This way we avoid transferring embryos that can cause serious illnesses or that cannot lead to a healthy or evolving pregnancy.
Preimplantation genetic testing for monogenic diseases (PGT-M)
This study tells us whether or not the embryos are affected by a serious family disease caused by variations (mutations) in a specific gene. Our DNA is made up of thousands of genes, each of them made up of a code that translates into a specific function of the organism. If this code varies (is mutated) it can lead to the disease.
PGT-M is indicated:
- In patients with a hereditary disease, in a member of the couple or in their family. In patients with a matching compatibility test for the same disease in both members of the couple, in order to avoid transmitting it to their offspring.
- To perform this type of test on embryos, it is essential to first carry out an Informativity Study. This study prior to PGT-M consists of carrying out genetic tests on the couple and their relatives in order to obtain more information about the disease and validate the diagnostic possibilities in future embryos.
Combined preimplantation genetic test (Combined PGT)
As its name indicates, this is a study that combines the two previous technologies.
It is indicated when there is an indication for PGT-M and, in addition, one of the circumstances or indications for PGT-A is present.
Genetic testing in the prenatal stage or during pregnancy
Hysteroscopy and chromosomal study of aborted remains
At Equipo Juana Crespo we care about knowing the reason for the pregnancy loss. That is why we carry out a genetic study of the fetal remains and possible causes of a spontaneous abortion. In 50% of cases the cause is chromosomal and can help us direct the treatment we carry out later.
Non-invasive prenatal test
This is a screening carried out during pregnancy (from week 10 of pregnancy onwards) that analyses the fetal DNA that circulates freely in the maternal bloodstream.
This is a non-invasive test that allows us to detect the presence of chromosomal alterations (aneuploidies) without having to resort to an invasive test. In the case of an altered result, confirmation by amniocentesis will be recommended.
Non-invasive prenatal testing is mainly indicated for:
- Women of advanced maternal age
- High-risk result in a biochemical or ultrasound screening
- History of pregnancy with chromosomal abnormalities
- Pregnant women of any age who have completed week 10 of pregnancy
- Pregnancies achieved naturally
- Pregnancies achieved by In Vitro Fertilization (IVF):
- With own gametes
- With gamete donation
- Single or twin pregnancies
