Test to detect Down Syndrome

The early detection of chromosomal abnormalities has always been a challenge for obstetricians who try to provide the maximum assurance to families that their baby will be born healthy. A few years ago, the non-invasive prenatal tests, which have revolutionized the way of dealing with prenatal diagnosis. He is one of the most common genetic abnormalities or trisomies.

The normal thing is that men and women have 46 chromosomes, of which we have inherited 23 from our mother and 23 from our father from the ovum and the sperm, which are the only cells in our body with 23 chromosomes, precisely for the purpose that when they unite they form a viable embryo with 46 chromosomes. These 46 chromosomes are distributed in pairs, that is, two chromosomes number 1, two chromosomes number 2 ... up to 23, which is the chromosome responsible for sex (XX for women and XY for men). At the same time, these pairs are formed with a chromosome from the father and another from the mother.

What happens when a chromosome is lost or gained?

Sometimes a wrong egg or sperm They can have a number of chromosomes other than 23, in this case the embryo they will give rise to is also wrong, because it would not add up to 46 chromosomes.

• The loss of a chromosome it causes an embryo with 45, which unless one of the X chromosomes is missing, cannot give rise to a live fetus.
• When you win a chromosome an embryo with 47 is generated, which is not compatible with life either, except when it occurs on chromosome 21. This chromosome is the smallest of all, so small that having one too many does not prevent the fetus from living , but it causes many disorders. In fact, they are affected by Down syndrome or trisomy 21.

Diagnosis of Down Syndrome: evolution

Until a few years ago the only way to diagnose chromosomal abnormalities was with ultrasounds through certain signs that could alert us to the possibility of chromosomal abnormalities. Another way is with an invasive test, that is, to obtain fetal material to perform laboratory tests that would rule out or confirm the diagnosis: amniotic fluid obtained through or material from the placenta obtained through.

These invasive tests, while safe, have a risk of approximately 1% of jeopardizing pregnancyWell, we are invading the habitat of the fetus. A few years ago, the non-invasive prenatal tests. They consist of performing very sophisticated laboratory tests from maternal blood that allow us to isolate chromosomal material from the fetus (specifically from the placenta, but which in normal conditions is identical to that of the fetus) and to inform us whether we are dealing with two or three copies of each of these chromosomes with one reliability close to 100%. Therefore, it could be known if it is a Down syndrome.

Down syndrome test instead of amniocentesis

The Down Syndrome test It is safe, the margin of error is very low and can be done from the week 10 of pregnancy (results in a week). Before, for an amniocentesis you had to wait until week 15 and the results took three weeks. For this reason, these tests have revolutionized the way of dealing with prenatal diagnosis. The woman, who previously resorted to one to confirm the normality of the pregnancy, now has an alternative that does not suppose no fetal risk.

Even so, not all are advantages, because this test also it has some drawbacks: It is a expensive test, has a minimum margin of error, but it does, there may be cases in which it is not possible to make the diagnosis and, in case of positive, it will be necessary to confirm with an invasive test.

• Until a few years ago the only way to diagnose it was by suspecting ultrasound, and subsequently performing a invasive test that could compromise the pregnancy.
• Now the non-invasive prenatal tests, allow the isolation of chromosomal material of the fetus (from the placenta) from maternal blood and have a reliable close to 100%
• The test is safe, the margin of error is very low and can be performed from week 10 of pregnancy, and in less than a week we have results

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Specialist in gynecology and obstetrics