A more accurate test that enables a pregnant woman to test her unborn child for Down syndrome without the risk of miscarriage has become available in South Africa, over the past two years. The Harmony Prenatal Test is a non-invasive cell free DNA (cfDNA) analysis method that makes it possible to analyze foetal DNA for Down syndrome by taking a sample of the mother’s blood, without posing any risk to mother or baby.
Doctors Shannon Morris and Karin Norman, directors of The Fetal Assessment Centre in Cape Town, decided to bring the test to South Africa after seeing clinical evidence of how it worked from the Harris Birthright Research Centre for Fetal Medicine in London.
What is Down syndrome and who is at risk?
Down syndrome is a genetic disorder that causes mental retardation and physical defects. It’s caused by the presence of an extra copy of chromosome number 21. Essentially what happens is at the time of conception; a baby inherits 23 chromosomes from its mother and 23 chromosomes from its father. In the case of a Down syndrome baby, the foetus inherits an extra chromosome. It’s this extra bit of genetic material that leads to Down syndrome.
This condition affects one in every 800 to 1,000 live births. Scientists assent that women older than 35 are more at risk of having a child with this condition. A woman who is 20 has a one in 1600 chance of conceiving a child with Down syndrome, while a woman in her 40s has a one in 100 chance and a woman older than 45 has a one in 30 chance. If you already have a child with this condition, you are more likely to have another Down syndrome child. And for every 100 couples who have another baby, One will have a second child who has Down syndrome.
Standard Procedures for Detecting Down syndrome
There are two types of prenatal tests available to detect Down syndrome in South Africa: screening tests and diagnostic tests. Screening tests estimate the risk that a foetus has the condition while a diagnostic test will confirm whether the foetus actually has Down syndrome.
- Blood tests. A mother’s blood levels can be measured of certain proteins and hormones. This, along with the mother’s age, will determine whether more tests must be conducted. These tests are usually done between 11 and 20 weeks of pregnancy
- Nuchal translucency testing. An ultrasound is done to scan nuchal translucency – the thickness of a layer of fluid that forms near the neck of a developing fetus. Too much liquid there is often a sign of Down syndrome. This test is correct 80 percent of the time, when considered along with the mother’s age. The Nuchal translucency test is done between 11-14weeks of pregnancy.
A test performed after the 12th week of pregnancy looks at the cells in the fluid that surrounds the fetus. This procedure holds about a half percent increased risk of pre-ter delivery or miscarriage.
- Chorionic-villus sampling (CVS)
During this test placental cells are analyzed for the chromosome abnormality and can be done as early as 10 and a half weeks of pregnancy. This procedure increases the risk of a miscarriage by about 1 percent.
Why the need for Cell free DNA Analysis
The standard methods for screening prenatal Down syndrome yield a higher false positive percentage than cfDNA analysis. When a positive result has been obtained by the screening method, a diagnostic test has to be carried out and this usually poses the risk of miscarriage. CfDNA analysis is therefore preferred because of its higher degree of accuracy (1 in 1000 false positive) and its harmless, non-invasive effect on the pregnancy and the unborn child.
The Harmony Prenatal Test
The Harmony Test is performed when a woman is about ten weeks pregnant.
As a baby develops, a small amount of their genetic information (cell-free DNA) passes into the mother’s blood. This cell-free DNA can be tested to give the most accurate estimation of the risk of a baby having Down syndrome. “With the Harmony test we are virtually 100% sure of whether your baby has Down syndrome,” says Dr Morris. “And we achieve this without any risk to mother or baby and without ever having to stick the needle in.”
However in 5% of women, these tests will have a false-positive result. This means that the test will indicate for Down syndrome when in fact the baby is perfectly healthy. These mothers may choose to have more invasive tests done to determine whether their baby has the chromosome disorder, but these carry a risk.
After the blood sample is taken at The Fetal Assessment Centre it is sent overseas to Ariosa Diagnostic laboratory in California, United States for analysis
“Ariosa has years of experience in cell-free DNA analysis which is why we opted to use their laboratory services,” says Dr Karin Norman.
And despite the distance travelled, the turnaround time for results is roughly 12 days.
“This means that we have the results before mothers come in for their 12 week scan, giving them increased peace of mind by providing early opportunities for making vital decisions during their pregnancies,” explains Dr Morris.
The biggest problem with the Harmony Test is that it costs some R8000.
This high price tag makes this test inaccessible to the state and therefore also to any mother who relies on public health care. And with medical aids being unwilling to foot the bill, only those who can afford to pay out of pocket are able to access the Harmony test.
Although this test is a major advance, it has its limitations and experts still maintain for a diagnostic test to be carried out after a positive result for Down Syndrome has been obtained.
Controversy of prenatal Down Syndrome Testing
It has become a controversial issue: should one screen for Down syndrome? If the foetus shows signs of having a genetic abnormality, what should you do? Is abortion an option?
Down Syndrome South Africa does not consider Down syndrome a reason for pregnancy termination. People with Down syndrome can lead and do lead full and rewarding lives and make a valuable contribution to our society. However the organization does acknowledge that mature aged women or those at high risk need to be in the knowhow of their unborn child’s condition in order to make the right decision for themselves.