When Does Down’s Syndrome Occur?
Down syndrome is a genetic variation that appears with an extra copy of chromosome 21. It occurs at the time of conception when the egg and sperm cells join, resulting in an extra chromosome in every cell.
In most cases, Down syndrome occurs due to a random variation during cell division in the egg or sperm cells, resulting in an extra copy of chromosome 21. The process is called non-disjunction, and it happens in about 95% of cases of Down syndrome.
Less commonly, Down syndrome can occur due to a genetic rearrangement called translocation, where a part of chromosome 21 attaches to another chromosome.
In rare cases, Down syndrome can occur due to mosaicism, where some cells have an extra copy of chromosome 21 while others do not. This occurs in only 2% of cases of Down syndrome.
Down’s Syndrome Screening
Expecting mothers have the chance to learn about their unborn loved ones with today’s prenatal screening and diagnostic tests. One of these tests includes genetic screening and a Down syndrome diagnostic test.
Down’s syndrome screening tests are non-invasive methods that determine the chance of a mother carrying a baby with chromosome variations. Prenatal screening tests for Down syndrome usually combine blood samples and ultrasound examination.
The first genetic screening test is made in the first trimester, between 11 and 14 weeks of pregnancy. Down’s syndrome diagnostic test indicates whether parents need additional diagnostic testing.
Below, we explain common non-invasive prenatal screening tests for Down’s syndrome.
The First Trimester Combined Test
The first trimester combined test involves two analyses that are recommended to be performed at the same time or within the same week.
- Blood test that calculates the levels of a PAPP-A protein (pregnancy-associated plasma protein A), which is an essential chemical compound in foetal development. Low levels of PAPP-A protein in the mother’s blood indicate that further analysis is needed.
- Nuchal translucency is an ultrasound screening test that measures specific parameters of the baby’s neck. Elevated levels of fluid in these specific areas may indicate potential chromosome variations.
Integrated Screening Tests
The integrated screening test is usually performed in the first and second trimester. The results from both analyses show the possibility of having a child with Down syndrome.
In the first trimester, the test involves a blood sample to measure the PAPP-A levels combined with an ultrasound check.
In the second trimester is performed a quadruple test is performed that measures the levels of estriol, inhibin A, alpha-fetoprotein and human chorionic gonadotropin – HCG.
Second trimester screening tests are usually recommended for women who had positive results on the first trimester screening test. However, many medical practices recommend second trimester screening (from the 14th to 20th week of pregnancy) if a woman’s age is estimated to have a link with the possibility of having a baby with Down syndrome, Edward syndrome or neural tube alterations.
Down’s Syndrome Diagnostic Tests During Pregnancy
If the screening test results showed a higher potential of having a baby with genetic mutations in chromosomes, some parents decided to perform additional diagnostic tests to confirm the diagnosis. These analyses are more invasive and provide more accurate information.
Common diagnostic tests for chromosome variations during pregnancy include:
- Amniocentesis
- Chorionic villus sampling CVS
- Percutaneous umbilical blood sampling PUBS
Amniocentesis Test
Amniocentesis is a prenatal test that collects amniotic fluid from around your baby in the mother’s uterus. This fluid sample indicates specific health conditions and variations related to the baby’s DNA and physical health.
Amniocentesis is a diagnostic test and shows the risks of potential health conditions of your baby, including:
- Congenital disabilities such as a change in the shape or function of the major organs that may impact the overall health of your baby (neural tube defects)
- Genetic chromosomal differences such as heart defects, Down syndrome, or cystic fibrosis
Amniocentesis is performed between 15 to 20 weeks of pregnancy, but it’s not recommended in early pregnancy because of the increased risk of miscarriage or other potential complications.
Chorionic Villus Sampling (CVS)
Chronic villus sampling, or CVS, is a prenatal test performed by taking a tissue sample from the placenta to test for chromosomal mutations or related genetic variations.
CVS is done between the 11th to 14th week of pregnancy in one of the following methods:
- Transcervical – in which a catheter is inserted through the cervix in the placenta to get a sample of the tissue
- Transabdominal – in which a needle is placed through the abdomen and uterus into the placenta to get a tissue sample
It’s important to highlight that CVS does not reveal information about neural tube defects, so people may need an additional blood test between 16 to 18 weeks of pregnancy to test for neural tube defects.
Percutaneous Umbilical Blood Sampling (PUBS)
Percutaneous umbilical blood sampling PUBS, or a test called cordocentesis, involves taking a foetal blood sample directly from the umbilical cord.
PUBS is a quick test typically done after the 18th week of pregnancy. It is invasive prenatal testing used when amniocentesis or chorionic villus sampling does not provide conclusive results.
PUBS is also used when there is suspected a low blood count, low platelet count or a thyroid problem in the baby.
The most common reasons for taking percutaneous umbilical blood test sampling include the following:
- Specific congenital disabilities noted on the ultrasound
- The other screening tests did not show conclusive results
- There is an issue of Rh incompatibility
- The baby may have an infection, like toxoplasmosis
PUBS comes with an increased risk of miscarriage or infection of the baby.
Postnatal Down’s Syndrome Diagnosis
After birth, doctors thoroughly examine the baby, including physical features, breathing and heart rhythm. If medical paediatricians notice any difference or characteristics that may indicate a Down syndrome, they will likely perform a further examination.
The next step is performing a blood test for Down’s syndrome, called a chromosomal karyotype, to confirm the assessment. If there is an extra chromosome 21 in some or all cells, it is evaluated as Down syndrome.
Physical Signs of Down Syndrome Post Birth
We are all born with different physical and psychological features. A child with extra chromosome 21 has distinctive characteristics that can be signs of Down syndrome.
Common physical features of children with Down syndrome include:
- Beautifully almond-shaped eyes that slant up
- Nose and face appear more flattened than the average
- Smaller size of the mouth
- Small white spots on the iris (coloured part of the eye)
- Neck size shorter than average
- Size of the ears is smaller than average
A postnatal diagnosis of Down syndrome can be overwhelming for parents. Still, it is essential to highlight that children with Down’s syndrome can live happy and fulfilling lives with appropriate care and support. It is important to work closely with healthcare providers to ensure that the child receives the best possible care and interventions.
What is Considered High Risk for Down Syndrome?
Chromosome variation of Down syndrome occurs by chance. However, there are some potential factors that might lead to the formation of extra chromosome copy 21 in children with Down syndrome.
Researchers relate the mother’s age with the potential chance of carrying a child with Down syndrome. More precisely, the possibility of having a child with Down syndrome grows with the mother’s age during pregnancy.
Based on statistics, numbers show that:
- Women aged 20+ have a 1 in 1,500 chance of carrying a baby with Down syndrome
- Women aged 30+ have a 1 in 800 chance of carrying a baby with Down syndrome
- Women aged 35-40 have a 1 in 270 chance of carrying a baby with Down syndrome
- Women 45+ have a 1 in 50 or higher chance of having a baby with Down syndrome
However, the statistical data only shows the average number of potential Down syndrome chromosome mutations in a child. These screening tests are not 100% accurate, and people who want more precise results may consider diagnostic testing.
Who Should Get a Screening Test?
Having prenatal screening testing is a matter of personal choice and decision. Whilst the accuracy of the results is still questionable, prenatal testing may indicate specific deficits in the baby’s physical development that may have a direct impact on their overall health and well-being.
In some cases, medical professionals may advise pregnant women to test for Down syndrome, including:
- Pregnant women over the age of 35
- Previously birthing a child with Down syndrome
- Family history
- Results indicating a higher possibility for Down syndrome in the prenatal testing
- Ultrasound checks indicating a difference in development
Unique Community Services Supports Women’s Health and Embraces Inclusivity in Social and Health Care
At Unique Community Services, we’re committed to providing support 24 hours a day, seven days a week.
Our professional team designs tailored care plans that cater to each individual’s unique needs and preferences. Our devoted staff provides the compassion, empathy, and support that people with Down syndrome need during their care journey.
Our clinicians are trained to assist people with Down syndrome in all daily activities, whether with learning activities, meal monitoring, or support with everyday tasks.
If you or your loved one need additional support, contact our offices in Bristol or Manchester for further information.
