Non-invasive prenatal testing (NIPT)

Non-invasive prenatal testing (NIPT) is a new approach to testing
whether a baby may be affected by a chromosome disorder. From a
small sample of the mother’s blood, we are able to identify certain
chromosomal conditions, such as Down syndrome.
During pregnancy, some of the baby’s DNA circulates in the mother’s
blood stream. DNA is the substance that our chromosomes are made of
and contains all our genetic information.
Usually, each human being has 46 chromosomes, arranged in 23 pairs.
Occasionally, a baby is born with three copies of a particular
chromosome, rather than two. This is known as a trisomy. The most
common trisomies are Down syndrome, Edwards syndrome and Patau
syndrome.
By analyzing the baby’s DNA found in the mother’s blood, we can
detect whether or not there are abnormalities in the baby’s
chromosomes.

What is Non-Invasive Prenatal Test (NIPT)?
Non-invasive prenatal testing (NIPT) analyses foetal ‘cell-free’ DNA
circulating in the pregnant mother’s blood. Foetal cell-free DNA
(cfDNA) results from the natural breakdown of foetal cells (presumed
to be mostly placental) in the mother’s circulatory system. It clears
from her system within hours of giving birth.
People usually have 46 chromosomes in each cell, but occasionally,
extra copies of chromosomes can be present, as is the case in Down
syndrome. Down syndrome is caused by an extra copy of chromosome
21. That is why it is sometimes called trisomy 21.
How is NIPT done?
The test is performed on a sample of the mother’s blood. About 10mls
of blood is taken from the arm – just like a normal blood test. The
blood is then sent to the laboratory for testing.
How safe is NIPT?
As it is a simple blood test, NIPT carries no significant risk to you or
your baby.
When is NIPT done?
From 10 weeks of pregnancy. Studies have shown that by 10 weeks
there is adequate foetal cell free DNA present in the mother’s blood to
conduct the test. The test is not recommended before that period.
Therefore, it is essential that you have had an ultrasound scan and
know the duration of your pregnancy and whether you are having one
baby, twins, or more.
If you have already had a scan early on in your pregnancy, then on the
day of the test (from 10 weeks onwards), another scan will be
performed to confirm foetal activity and heartbeat.

How accurate is NIPT?
NIPT for Down syndrome is more than 99% accurate. This means that
the test detects more than 99 out of 100 cases of Down syndrome, so
there is only a very small chance that the test will not detect an
affected pregnancy.
There is also a small chance that the test will incorrectly show that the
baby has Down syndrome when it does not. This is known as a false
positive result.
Even though the test is highly accurate, there is still a very small
chance (around 1 in 300) of an incorrect result. Therefore, if the result
of your NIPT predicts that the baby has Down syndrome, you will be
offered an invasive test to confirm the result.
What types of chromosomal abnormalities does NIPT detect?
NIPT will detect the most frequent trisomies
A trisomy is caused by the presence of three copies of a chromosome
instead of the regular two.
NIPT detects the following trisomies:
• Trisomy 21, or Down’s Syndrome, is the most common trisomy.
• Trisomy 18, or Edward’s Syndrome, has a high incidence of
miscarriage or late foetal deaths
• Trisomy 13, or Patau’s Syndrome, is related to a high incidence
of miscarriage. This chromosomal abnormality has a high foetal
mortality rate.
Alterations in sex chromosomes
NIPT also detects alterations in the number of sex chromosomes,
including:
• Turner Syndrome (45, X), the absence of an X chromosome
in girls.
• Klinefelter’s Syndrome (47, XXY),- the presence of an extra copy
of the X chromosome in boys.
Microdeletions and other trisomies
NIPT offers the option to analyze small changes in chromosomes,
known as microdeletions, as well as trisomies in chromosomes
16 and 9.
Few NIPTs can be performed after IVF treatment, including egg
donation and is also suitable for twins.
How long does it take to get the results from NIPT?
Usually results will be available within five working days.
In a very small number of cases the laboratory may be unable to obtain
your results. This might be because there was not enough of the baby’s
DNA present in the blood sample to obtain a result. If this happens,
then, the option of repeating NIPT will be explored.

What are the possible results?
• No aneuploidy detected
Your baby is very unlikely to have Down syndrome, Edward
syndrome or Patau syndrome
• Aneuploidy detected
It is very likely that the baby is affected with Down syndrome,
Edwards syndrome or Patau syndrome. You will be offered an
invasive test (see below) to confirm this result. This is offered
because very occasionally, in around 1 in 300 cases, NIPT may not
accurately reflect the result in the baby.
• Inconclusive result
As this is a new test we occasionally get an inconclusive or
‘unclear’ result. If we cannot detect a clear result, we will inform
you and offer you another NIPT test.
• Failed result
Occasionally we get a failed result, if this happens we will offer
you a repeat NIPT test at no additional cost.
How does NIPT compare with other screening tests currently offered
during pregnancy?
The traditional screening test offered during pregnancy, which consists
of an ultrasound scan and a blood test (or in some cases only a blood
test), is less accurate than NIPT. The traditional test detects 84-90% of
babies with Down syndrome.
What happens if the NIPT result predicts the baby has Down,
Edwards or Patau syndrome?
If the NIPT result shows the baby has one of these chromosomal
problems, you will be offered an invasive test. Invasive tests give a
more definitive ‘yes’ or ‘no’ result as to whether the baby has Down
syndrome or other common trisomy.
There are two types of invasive tests:
Chorionic Villus Sampling (CVS)
this is usually performed between 11 and 13 weeks.
Amniocentesis
usually performed from 15 weeks of pregnancy.
Both procedures involve using a fine needle to collect a small sample
of either the amniotic fluid that surrounds the baby (amniocentesis) or
a small sample of cells from the placenta (CVS). These tests carry a
small risk of miscarriage of 0.5% to 1% in the UK. This means that for
every 200 women who have a CVS or amniocentesis, one or two of
them will miscarry due to the test.

What else should I consider before taking this test?
Before making a decision about NIPT, you may want to take some time
to consider the test and discuss it with your partner. Think about how
you might feel about the test results and how important the information
would be for you and your family. Some couples feel that they
may not continue with the pregnancy if a chromosome disorder was
found. Others would continue whatever the results but would like to
know in advance in order to prepare for the arrival of their baby.
If you are unsure about anything, it can be helpful to discuss it with
your healthcare professional. Where can I get further information and
support?

This article was submitted by leading London Gynecologist Mahantesh Karoshi