Trisomy is a genetic condition that occurs when a baby is born with an extra chromosome. There are several different types of trisomy disorders, with the most common being Down syndrome, Klinefelter syndrome, Triple X syndrome, and Edwards' syndrome.
Expecting parents should be aware of trisomy and the potential impact it can have on a child. In this guide, we'll be sharing the most important facts relating to trisomy, including common causes of trisomy and how to test for trisomy.
5 Trisomy Facts You Should Know
1. Trisomy is genetically transmitted
Although most people assume that conditions like Down Syndrome occur randomly, they are genetically transmitted the vast majority of the time. The genetic makeup of both parents will determine how much risk a child has of developing trisomy. Trisomy occurs whenever an extra copy of a certain chromosome appears in a baby during prenatal development.
2. There are 6 common types of trisomy
The 6 common types of autosomal trisomy are:
- Trisomy 21 (a.k.a. Down syndrome)
- Trisomy 18 (a.k.a. Edwards syndrome)
- Trisomy 13 (a.k.a. Patau syndrome)
- Trisomy 9
- Trisomy 8
- Trisomy 22
3. Most babies with trisomy don’t survive the second or third trimester
Trisomy is a very dangerous condition that puts the baby in great danger. It is important to diagnose the condition as quickly as possible so treatment can be obtained.
4. About 1 in 700 babies has trisomy 21
Down Syndrome is the most common trisomy defect, affecting about 1 in 700 babies. Edward’s syndrome is the second-most common, impacting about 1 in 5000 babies.
5. Trisomy mostly affects female babies
Female babies are more likely to be affected because female chromosomes are prone to becoming infected at a faster rate than male ones.
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Common Causes of Trisomy
Under normal circumstances, a baby will inherit two copes of each chromosome from their parents. Trisomy occurs when they inherit a third copy of a chromosome. In most cases, the third chromosome will come from the maternal side, but that is not always the case.
Signs and symptoms of Trisomy
The signs and symptoms of trisomy will vary based up the affected chromosome. However, the most common symptoms include:
- An unusual facial profile
- Larger or smaller heads, ears, nose, and mouth
- Unusually shaped eyes or close-set eyes
- Poor muscle tone
- Learning disabilities
- Malformations in the skull or brain
Prenatal Tests for Detecting Trisomy
There are several tests which can detect if a child has trisomy, including a number of pre-natal tests. They are:
NIPT (Non Invasive Prenatal Testing)
This test checks maternal blood to determine if there are any chromosomal anomalies. This test can be performed at any time with minimal risk to mother or baby.
NTD (Neural Tube Defect Screening)
This prenatal test can be performed when the foetus is between 16 to 18 weeks of age. A detailed ultrasound is performed to determine if a neural tube defect exists. Most women opt to have this test instead of a blood test.
Down Syndrome Screening
This test can be performed within the first or second trimester to check if a baby has down syndrome. It involves a blood test which looks for hormones that are associated with the development of Down syndrome.
Trisomy 18 Screening
This test is similar to down syndrome screening, in that it checks for specific hormones relating to trisomy 18.
CVS (Chronic Villus Sampling)
This test involves the extraction and analysis of some of the chorionic villi, which are tiny growths in the placenta. It checks if more than two chromosomes are present in the tissue. It is an extremely accurate test, but slightly more invasive than other tests.
This prenatal test involves a small amount of amniotic fluid being extracted from the amniotic sac surrounding the foetus. In addition to checking for chromosomal abnormalities, this test can look for foetal infections and check the gender of the child.