NIPT Scan (Down’s syndrome Testing)
Non-Invasive Prenatal Testing (NIPT) is a safe and highly accurate scan and blood test. It is intended to help expectant parents assess the likelihood of chromosomal conditions in their unborn baby. At Sonoclinic, we conduct this test primarily to screen for:
- Down’s syndrome (Trisomy 21)
- Edwards’ syndrome (Trisomy 18)
- Patau’s syndrome (Trisomy 13)
How NIPT Works
NIPT analyses cell-free foetal DNA (cfDNA) present in the mother’s bloodstream. A small blood sample from the pregnant mother is examined to detect potential chromosomal abnormalities. Since this test is non-invasive, it poses no danger to the baby, unlike invasive procedures such as amniocentesis or chorionic villus sampling (CVS).
Accuracy and Predictive Values
NIPT is highly reliable, with a 99% detection rate for Down’s syndrome, Edwards’ syndrome, and Patau’s syndrome. It is, however, a screening test, and while it provides a probability, a high odds result does not make the diagnosis. Further diagnostic testing, such as amniocentesis or CVS, is recommended for confirmation.
The positive predictive values (PPV) indicate the likelihood that a high-probability result is a true positive:
- Down’s Syndrome (Trisomy 21) - 82%
- Patau’s Syndrome (Trisomy 13) - 49%
- Edwards’ Syndrome (Trisomy 18) - 37%
Comparison with Traditional Screening
NIPT is more accurate than traditional first-trimester combined tests or second-trimester quadruple tests, which can miss 15% or more of Down’s syndrome cases. NIPT has a false-positive rate of just 0.13% for Down’s and Edwards’ syndrome and 0.01% for Patau’s syndrome, making it a more reliable option.
When Can You Undergo the NIPT?
You can have the NIPT from 10 weeks of pregnancy. Before the blood test, an ultrasound scan is carried out to:
- Confirm the pregnancy is beyond 10 weeks
- Detect the baby’s heartbeat
- Find out if it is a single or multiple pregnancy
- Provide an accurate pregnancy dating
The blood test cannot be done if the pregnancy is less than 10 weeks. Therefore, you may need to return later.
Preparation for the NIPT
To ensure accurate results, follow these simple preparation steps:
- Carry with you any paper or digital medical records you may have.
- Approximately one hour prior to your NIPT appointment, consume a litre of clear fluid.
- Avoid urinating before your consultation. This will provide us with the finest view of the infant.
- Put on a two-piece outfit (such as a top with trousers or a skirt) to allow easy access to your abdomen for the scan.
What If Results Are Inconclusive?
In rare cases (less than 1%), results may be inconclusive as a result of low foetal DNA levels in the sample. If this happens, a repeat test may be recommended later when foetal DNA levels are expected to be higher. However, some individuals naturally have low foetal DNA levels, which may prevent obtaining a conclusive result.
NIPT vs. Nuchal Translucency (NT) Scan
Nuchal Translucency (NT) Scan measures fluid at the back of the baby’s neck via ultrasound and combines this with a blood test to estimate the risk of Down’s syndrome.
NIPT directly analyses foetal DNA, offering greater accuracy than the NT scan.