What is non-invasive prenatal (NIPT) testing?

Pregnancy can be a joyous yet chaotic time. From the first time you discover you’re pregnant, the first time you see a little heartbeat on the ultrasound, to the seemingly endless nausea and vomiting, and finally, the sigh of relief when you hear a cry for the first time — there is never a dull moment.

During your prenatal appointments, one of the tests your doctor may offer is called NIPT testing. The test helps doctors to pinpoint a baby’s risk for several genetic disorders, including Down syndrome. This article explains what is NIPT and how it works.

What is NIPT and what does it screen for?

NIPT stands for non-invasive prenatal testing, or sometimes referred to as noninvasive prenatal screening (NIPS). The test allows doctors to detect the risk that the foetus will be born with certain genetic abnormalities. The test is safe and allows for detection without risk to the foetus.

The three most common syndromes the tests screen for are:

• Down Syndrome (Trisomy 21)
• Edward Syndrome (Trisomy 18)
• Patau Syndrome (Trisomy 13)

How does NIPT screening work?

During pregnancy, the unborn baby releases some of its DNA into the maternal blood. By taking a sample of the mother’s blood we can pick out the baby’s DNA and analyse it for chromosomal abnormalities.

OT&P Obstetrician Dr Zara Chan.

The NIPT is considered non-invasive because it involves drawing blood with a needle and syringe from the mother's arm. It’s done between the 11th and 14th week of gestation and does not pose any risk to the fetus. Your sample will then be sent to a lab to check for signs of abnormalities.

In addition to testing for abnormalities of chromosome 21,18, and 13, NIPT is also able to detect the baby’s sex and look for sex chromosome abnormalities. The exception being when the pregnancy is a twin or higher-order pregnancy. In the case of identical twins, the laboratory will assume both babies contribute equally to the DNA sample. However, in non-identical twins or vanished twins, this cannot be assumed and hence the test will not be able to proceed.

How accurate is the test?

Currently, various laboratories do the test, all with more than 99% accuracy and a false positive rate of 0.1-0.4%¹.

Despite its high detection rate, it’s important to note that the test is not 100% as it’s only a screening test. This means that even though a result can be positive, it cannot be certain that your baby is affected by a genetic condition, but rather, its an estimate of whether the risk of having a certain condition for your baby is increased or decreased.

In most situations, if the test is positive your doctor will discuss with you further test options to confirm the diagnosis.

OT&P Obstetrician Dr Zara Chan

The confirmatory tests are either chorionic villi sampling (CVS) or amniocentesis. The choice of either test will depend on how advanced your pregnancy is, the expertise available and your personal choice. However, the confirmatory tests are considered invasive tests and carry a miscarriage rate of 0.5 to 1%. You should discuss your options at length with your doctor.

NIPT vs. FTS screening

Prior to the introduction of NIPT, women were testing for the three syndromes using first trimester combined screening (FTS). This screening calculates the baby’s risk of having any of the syndromes using a combination of baby’s neck fold thickness, maternal age, background risk and specific pregnancy proteins (e.g. beta-hCG, PAPP-A). This is done by:

• A blood test to measure levels of pregnancy-specific proteins in the mother's blood (PAPP-A and beta-hCG)
• An ultrasound exam to measure the size of the baby’s neck fold thickness.

This method has a detection rate of approximately 90%². Although NIPT is superior³ to FTS in its detection rate, both are still only screening tests.

How OT&P Obstetricians can help

NIPT is a wonderful technology that provides us with noninvasive options to determine the baby’s well being. It can offer a peace of mind during your pregnancy knowing about your baby’s health and development.

While getting the test done is pretty straightforward, for most mothers, seeing the results can be scary. It’s important that you discuss with your doctor all your options, and what a positive test result can mean. Finding out about any potential conditions early on can allow you to prepare for any special requirements and hard decisions, such as making plans to facilitate the delivery or even terminate the pregnancy. All in all, please discuss with your doctor whether the NIPT test is for you.

References

1. Nicolaides, K., Syngelaki, A., Ashoor, G., Birdir, C. and Touzet, G. (2012). Noninvasive prenatal testing for fetal trisomies in a routinely screened first-trimester population. American Journal of Obstetrics and Gynecology, 207(5), pp.374.e1-374.e6.

2. Gil, M., Quezada, M., Revello, R., Akolekar, R. and Nicolaides, K. (2015). Analysis of cell-free DNA in maternal blood in screening for fetal aneuploidies: updated meta-analysis. Ultrasound in Obstetrics & Gynecology, 45(3), pp.249-266.

3. Tamminga, S., van Schendel, R., Rommers, W., Bilardo, C., Pajkrt, E., Dondorp, W., van Maarle, M., Cornel, M. and Henneman, L. (2015). Changing to NIPT as a first-tier screening test and future perspectives: opinions of health professionals. Prenatal Diagnosis, 35(13), pp.1316-1323.