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The prenatal diagnosis cytogenetic to confirm or rule out the presence of a chromosomal abnormality in the fetus.
Expert: Guillermo Lay-Son, a geneticist at children's Clinic German
The chromosomal abnormalities can cause miscarriage, as well as various congenital anomalies associated with a delay in fetal growth.
There are different disorders that can affect the chromosomes, being the abnormalities in their number the most recognized at a general level. Among these stand out:
  • trisomy 21 (Down syndrome)
  • trisomy 18 (Edwards syndrome)
  • trisomy 13 (Patau syndrome)
  • monosomy X (Turner syndrome)
  • syndrome 47, XXY (Klinefelter's syndrome)

What is the cytogenetic diagnosis prenatal?

This allows to confirm or rule out the presence of a chromosomal abnormality in the fetus in pregnancy. The genetic information is contained within structures of the cell nucleus called chromosomes.
As usual, we have 46 chromosomes, being 23 of them contributed by each parent. This type of study allows to visualize and to directly analyze the chromosomes under a microscope.

What problems can lead to abnormalities in the chromosomes?

These can cause various problems. For example, are the cause of half of all miscarriages during the first trimester of pregnancy. At the time of delivery, affecting 1 in 160 newborns, which may cause anomalies of physical variables associated with a delay in fetal growth, on many occasions.

What are the problems most common chromosomal that can affect the fetus?

Trisomies, which are when the affected individuals have three copies of a particular chromosome, instead of two. Usually, they are generated when they are forming eggs and sperm, in a process called meiosis.
This allows each parent transmits half of the genetic information to their children. Are errors that occur without a known cause, although it is known that there is a risk that is increasing with maternal age, especially from 35 years of age.
Although you may have trisomies for almost all chromosomes in human, can only come to an end the trisomies 13, 18 and 21. In the case of trisomies 13 and 18 present a set of congenital anomalies which are associated with improved survival overall between seven and 14 days. Very few children exceed the year of life.
In contrast, the trisomy 21 or Down syndrome is the chromosomal abnormality most common in newborns. In our country, approximately 1 in every 400-450 babies is born with this condition.
The importance of establishing an early diagnosis is to be able to prepare the families and the medical team to take early actions to the health problems that often manifest, as well as to encourage the early stimulation and inclusion.
Currently, the vast majority of these children reached adulthood, and progressively have more opportunities in our society.
The monosomy, in both, consisting in the absence of one of the chromosomes, are incompatible with life, except for the monosomy of the X chromosome, which causes Turner syndrome: girls that have essentially cut low with problems in the development of puberty and fertility.
Some may also present with congenital anomalies kidney and heart.

When is it indicated to perform a chromosome study in pregnancy?

The indications to perform a cytogenetic study prenatal mainly include the suspicion of a chromosomal abnormality based on the ultrasound findings, and/or in methods of screening biochemical.
It is also indicated by a history of the family history and reproductive of the couple, as in the case of that one of the parents is carrier of a chromosomal abnormality or maternal age is advanced, about 35-38 years.
What is optimal is that each couple need to perform this type of studies have a proper process of advice or genetic counselling, where they can inform about the potential benefits and risks associated with the procedure.

How and when you can get the sample to study?

To make a cytogenetic diagnosis prenatal is necessary to obtain a sample with vital cells of the fetus, so that they are considered invasive methods.
You can perform a chorionic villus sampling to obtain cells of:
  • trophoblast (placenta)
  • vagina (transcervical)
  • abdomen (transabdominal)
Is made, usually, between 11 and 14 weeks of gestation.
You can also practice an amniocentesis, which allows you to analyze fetal cells present in amniotic fluid and is usually performed from week 16.
Finally, cordocentesis, is the removal of fetal blood directly from the umbilical cord for analysis of lymphocytes. Usually done from 18-20 weeks of gestation.

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