Down syndrome - causes, consequences and how it is detected during pregnancy

What is Down Syndrome?

Down syndrome is a genetic condition that occurs when an individual has an extra copy of chromosome 21. This additional genetic material impacts physical development, cognitive abilities, and sometimes health, but it does not define a person’s potential or worth. People with Down syndrome lead fulfilling lives, build meaningful relationships, and contribute to their communities in extraordinary ways.

What are the main symptoms and characteristics of Down syndrome?

People with Down syndrome have specific physical characteristics. Recognizable physical characteristics include mongoloid, i.e. slanted eyes (the appearance of the "third eyelid"), and white spots are also visible on the iris. There is a reduced head circumference and a small nose. The mouth is also small, while the tongue is thicker and wider, so it often protrudes from the oral cavity. Teeth grow late, and numerous irregularities in the shape and number of teeth are noticeable. The ears are small and set low, often poorly formed. On the palms, there is a noticeable "furrow of four fingers", while the hands themselves are wide and the fingers are short. Muscle tone is often very low, and the joints are extremely flexible.

The characteristic clinical picture further concerns mental development and health problems affecting the internal organ systems. When it comes to mental development, there is mostly moderate (IQ 40-50), and less often severe mental retardation. Congenital anomalies of the heart and other internal organs are also noticeable. Statistics indicate that as many as half of babies born with Down syndrome have a congenital heart defect. That is why timely diagnosis in the first months of life is crucial for early detection and treatment of heart problems. A smaller percentage of children are born with anomalies of the digestive tract, which mainly involve problems with the esophagus and intestines. More than half of people with Down syndrome are born with visual and hearing impairments, which can lead to delays in speech development. Early intervention will lead to a more advanced development of the senses, which will consequently allow the child's speech to develop properly. The immune system is generally not at an enviable level, so persistent infections, especially of the upper respiratory tract, often occur. There is also an increased risk of convulsions and leukemia in early childhood, which can have a fatal outcome.

How to diagnose Down syndrome in pregnancy?

Non-invasive prenatal tests - principle of operation: NIPT analyzes free fetal DNA circulating in the mother's blood. These tests are usually carried out from the 10th week of pregnancy. Accuracy: NIPT has a high accuracy rate (over 99%) in detecting Down syndrome, making it one of the most reliable prenatal tests available today.

1. Double test: The double test is a prenatal screening test used to assess the risk of chromosomal abnormalities, including Down syndrome (trisomy 21). This test is usually carried out between the 11th and 14th week of pregnancy and involves a blood test of the pregnant woman and an ultrasound scan.

Components of Double Test: Blood test: Blood samples are taken from the pregnant woman to measure the levels of certain hormones and proteins. In the Double test, the following are most often measured: Free β-hCG (free beta-hCG) PAPP-A (pregnancy-associated plasma protein A)

Ultrasound: An ultrasound examination is performed to help assess the thickness of the neck region (nuchal translucency), which is an additional indicator of the risk of Down syndrome.

How are the results interpreted? The results of the Double test are expressed as a risk (for example, 1 in 200), which indicates the probability that the fetus has Down syndrome.

Low risk: Usually considered a risk of less than 1 in 270.
High risk: A risk greater than 1 in 270 is usually considered a positive result, which may require further testing.

2. Triple test

The triple test is a prenatal screening test used to assess the risk of chromosomal abnormalities, including Down syndrome (trisomy 21). This test is usually performed between the 15th and 20th week of pregnancy and involves analyzing the pregnant woman's blood to measure the levels of three specific biomarkers.

Components of the triple test:

Biomarkers:
The triple test measures the levels of three substances in a pregnant woman's blood:
Alpha-fetoprotein (AFP): A protein produced by the fetus and found in the mother's blood.
hCG (human chorionic gonadotropin): A hormone produced during pregnancy.
Unconjugated estriol (uE3): an estrogen form that is also produced during pregnancy.

How are the results interpreted?

The results of the triple test are expressed as a risk assessment. For example, the risk may be expressed as "1 in 250", which means that there is a 1 in 250 chance that the fetus will have Down syndrome.

Low risk: A risk of less than 1 in 270 is usually considered low.
High risk: A risk greater than 1 in 270 requires additional testing to confirm or rule out the presence of Down syndrome.

Ultrasound

Ultrasound is used as a screening tool for the risk of Down syndrome (trisomy 21) and other chromosomal abnormalities during pregnancy. Although an ultrasound alone cannot diagnose Down syndrome, certain features that can be seen during an ultrasound examination can help assess the risk.

Key aspects of ultrasound in detecting Down syndrome:

Nuchal translucency (NT): This is a measurement of the thickness of the space under the skin on the neck of the fetus. Increased thickness may be indicative of a higher risk of Down syndrome. These measurements are usually taken between the 11th and 14th week of pregnancy.

Morphological ultrasound: It is performed between the 18th and 22nd week of pregnancy to assess fetal development and detect any abnormalities. While it cannot confirm Down syndrome, it can indicate other signs associated with chromosomal disorders.

Characteristics of the fetus: Certain characteristics, such as a short neck, specific facial features (eg, a round face), or abnormalities in the development of the heart, may be risk indicators for Down syndrome.

3. Amniocentesis: Amniocentesis is an invasive prenatal test used to diagnose chromosomal abnormalities, including Down syndrome (trisomy 21). This test is usually recommended when the results of screening tests (such as the Double or Triple test) indicate an increased risk or when there are other indications for additional testing.

How amniocentesis is performed:

Procedure:
Amniocentesis is usually performed between the 15th and 20th week of pregnancy.

The doctor uses ultrasound to locate the amniotic fluid, then uses a thin needle to take a sample of the amniotic fluid that contains fetal cells.

The procedure takes a few minutes, and most women can resume normal activities shortly after the test.

Sample analysis: Fetal cells from the amniotic fluid are analyzed to determine whether the fetus has Down syndrome or other chromosomal abnormalities.

Advantages of amniocentesis: High accuracy: Amniocentesis provides very accurate information about the chromosomal status of the fetus, with an accuracy of over 99% for the diagnosis of Down syndrome. Direct testing: Testing is performed on fetal cells, which allows direct determination of the chromosomal structure.

Risks and limitations:
Possible complications: Although the risk is low, amniocentesis carries the possibility of miscarriage (about 1 in 300 to 1 in 1,000 cases), as well as potential infection or injury to the fetus.

Invasiveness: Due to its nature, amniocentesis is an invasive procedure that can cause anxiety in pregnant women.

Celebrating Uniqueness

Individuals with Down syndrome remind us that every person has inherent value, potential, and beauty. By celebrating their achievements and supporting their needs, we enrich our communities and our lives. Together, let’s work toward a future where everyone, regardless of their abilities, is empowered to thrive.