How to detect most common trisomies

The human body is an incredible sum of various parts. In order to function normally, all its components must behave as intended, even those at the microscopic level and especially our DNA. Despite being microscopic, DNA determines the characteristics of each and every individual.

Our genetic record is stored in 23 pairs of chromosomes. At birth, each parent contributes half of the chromosomes.

These chromosomes are so important that any malformation has a major effect on embryonic development. If one of the parental sex cells contains 1 additional chromosome, a trisomy will occur, causing problems and complications.

There are three trisomies that every expectant mom should know about – trisomies 21, 18, and 13. These are the ones that most commonly occur during pregnancies.

Trisomy 21 – Down syndrome

The most common chromosomal abnormality present at birth is the trisomy of the 21st chromosome, also known as Down syndrome. The risk that a baby will have this syndrome increases with its mother's age – at 30 the chances are 1 in 1000, at 35 the risk rises to 1 in 400. 30% of pregnancies with trisomy 21 end in miscarriage.

Children with Down syndrome usually have mild to moderate cognitive impairment. Proper early upbringing is key to a normal and relatively independent life.
Down syndrome can be recognised by typical facial features, low muscle tone (hypotonia), heart diseases, and many other disorders. Only 1% of Down syndrome cases are hereditary.

Nevertheless, it is the mildest trisomy among the three most common ones, as people with milder syndromes can live relatively normal lives.

Trisomy 18 – Edwards syndrome

An additional chromosome 18 occurs in about 1 in 1000 pregnancies and is around three times more common in girls. Edwards syndrome is usually not compatible with life, as 80% of such pregnancies sadly end in miscarriage and less than 10% of infants survive for longer than a year.

Ultrasound examinations of pregnant women can detect symptoms. Infants with Edwards syndrome usually have low weight and other noticeable signs – small jaw, smaller ears, underdeveloped fingers, and more. Soon after birth, the babies start showing signs of a mental disorder.

Many children with Edwards syndrome have congenital heart diseases and kidney problems. Genetic studies suggest that most cases of the trisomy of the 18th chromosome are not hereditary.

 

Trisomy 13 – Patau syndrome

Like Edwards syndrome, Patau syndrome also occurs in about 1 in 1000 pregnancies. As many as 97% of such pregnancies end in miscarriage, and the vast majority of infants do not live past the first 4 months. Most cases of trisomy 13 are not hereditary.

Patau syndrome often causes heart and brain malfunctions, spinal problems, seizures, mental health problems, and other issues. At birth, a cleft lip or palate, underdeveloped eyes, clenched fist, extra fingers, and other anomalies can be seen.

 

As the risk of trisomies increases with the age of the expectant mother, it is especially advisable for women over 35 to take a prenatal test.

Among the most popular is the NIPT test, which is very simple and non-invasive. It can be performed as early as the 10th week of pregnancy and is completely risk-free for the mother and the baby. NIPT detects the three most common trisomies with more than 99% sensitivity. You can read more about the NIPT test and where to take it here.

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