Non-Invasive Pre-Natal Screening (NIPS) can help identify if your baby is likely to have a chromosomal condition.
Normally, all cells in the human body have 46 chromosomes, made up of 23 pairs of chromosomes. These 23 pairs of chromosomes contain all of the DNA, or building blocks, to determine the health of the fetus. Certain syndromes can occur when a fetus develops with three copies of a particular chromosome instead of two. Depending on the syndrome, the fetus may develop with significant abnormalities and in some cases may be fatal.
The risk of having a chromosomal condition increases as the mother gets older.
NIPS-What can be tested for and what is involved
What does NIPS test for?
- Down Syndrome (Trisomy 21)
- Edwards Syndrome (Trisomy 18)
- Patau Syndrome (Trisomy 13)
- Triploidy (Extra copies of all chromosomes)
- Monosomy X (Turner Syndrome) – optional
- Microdeletions (Missing piece of a chromosome) – optional
- Gender- Male(XY) Female (XX)-optional
When can NIPS be performed?
A blood test can be performed from 9 week’s gestation. From the blood, fetal DNA is analysed which will provide an estimate of risk of common chromosomal abnormalities.There is no risk of miscarriage associated with this screening test.
What will NIPS involve?
Firstly, an ultrasound scan will be performed in order to confirm how many weeks pregnant you are. Our staff will then discuss the test with you and answer any questions you may have before taking the blood sample.
Are all pregnancies suitable to undergo NIPS?
Almost all pregnancies can avail of NIPS, including twin pregnancies, egg donor or surrogate pregnancies. Pregnancies in which there has been a loss of one fetus early in the pregnancy (“Vanishing Twin”) are not suitable, nor are twin pregnancies from donor egg.
In the vast majority of cases (over 95%) the chances of passing on an extra chromosome are determined by the mother’s age. The older a woman is when she gets pregnant, the higher the chance that an extra chromosome will be passed on. It is important to realise that any woman can have a baby with Down syndrome, regardless of her age. For example, a 20 year old woman has about a 1 in 1,000 risk of passing on an extra chromosome causing Down syndrome, while a 40 year old woman has about a 1 in 70 chance of this happening. For most parents, the chances of having a baby with Down syndrome have nothing to do with family history or how healthy other pregnancies were.
Down syndrome is probably the most common cause of mental retardation. Babies with Down syndrome tend to develop more slowly than other babies do. For example, they may start walking later than other babies. About half are born with heart defects, or with a blockage in their intestines that prevents them from digesting food properly. These heart and intestine problems are usually fixed by surgery. Most children with Down syndrome go to regular schools, but special additional resources are usually made available as they grow and develop.
Like Down syndrome, this condition occurs when there is one extra chromosome, but in this case it is an extra chromosome number 18. Trisomy 18 is often also called Edwards syndrome. In the vast majority of cases, the chances of having a baby with Edwards syndrome are also related to the mother’s age. However, Edwards syndrome is much rarer than Down syndrome. For example, a 20 year old woman has close to a 1 in 2,000 risk of passing on an extra chromosome number 18, and a 40 year old woman has close to a 1 in 150 chance of this happening.
Another big difference between Edwards syndrome and Down syndrome is that Edwards syndrome is usually considered to be lethal, with very little possibility of the baby surviving. This is because most babies with Edwards syndrome have severe mental retardation, serious heart defects, and problems with development of the brain, spine, kidneys, or intestines. Most fetuses with Edwards syndrome are very small and don’t grow very well in the womb. About two-thirds of all fetuses with Edwards syndrome die in the womb before birth. A small number of babies born alive with Edwards syndrome may even survive for a few months, but this is quite rare.
Trisomy 13 is quite rare, occurring in about 1 in 5,000 births. Like Down syndrome and Edward syndrome, it is caused by one extra chromosome, this time a chromosome number 13. Also called Patau syndrome, the chances of it happening are determined by the mother’s age in most cases.
Like Edwards syndrome, Patau syndrome is usually considered to be lethal, with virtually no possibility of the baby surviving. Almost all babies with Patau syndrome have severe abnormalities, like serious heart defects, and problems with development of the brain, face, kidneys, limbs or intestines. Rare cases of Patau syndrome may survive for a few months after birth.
This is caused by an extra copy of all chromosomes. Abnormalities are often present in both the placenta and the fetus. It is found in about 1 in 1000 first trimester pregnancies. For most babies this is considered a lethal abnormality. Of those rare babies born alive, most die before one year of age. Mothers carrying a baby with Triploidy can also experience various pregnancy complications such as pre-eclampsia, severe nausea, excessive bleeding and rarely persistent placental disease.
Monosomy X & Microdeletions (optional)
Monosomy X is caused by a missing copy of the X chromosome and is also known as Turner Syndrome. This only affects girls and is found in 1 in every 5000 live births.
A Microdeletion is a small missing piece of a chromosome. Five microdeletion syndromes can be screened for:
- 22q11.2 deletion syndrome (DiGeorge)
- 1p36 deletion syndrome
- Angelman syndrome
- Prader-Willi syndrome
- Cri-du-chat syndrome
Results and accuracy
How will I receive my results?
The blood sample is sent to a genetics laboratory for testing and your results will be available in approximately 10 working days. You will receive a telephone call or email explaining the test results.
What do the results mean?
The test does not give a definitive result. Instead, the test will give a High Risk or Low Risk result for each of the outlined conditions.
If you receive a High Risk result an invasive test such as a chorionic villus sampling (CVS) or an amniocentesis will be advised in order to confirm the diagnosis.
If you receive a Low Risk result it is unlikely that you would need an invasive test, unless other risk factors are present, as it is extremely unlikely the fetus has one of the syndromes that have been screened.
How accurate is NIPS?
This screening test can detect up to 99% of the abnormalities of chromosomes 21, 18 and 13.
Monosomy X (Turner Syndrome) has a lower detection rate and lower positive predictive value. Therefore we don’t routinely carry out this test among the general population in the absence of other risk factors, however it may be performed upon patient request.
*In a small number of cases we receive an inconclusive result. This means we cannot detect a clear result and you will be offered a repeat test.