NIPT: non-invasive prenatal test using fetal DNA

NIPT (Non-Invasive Prenatal Test) is one of the most important advances in prenatal medicine in recent years. With a simple blood draw from the mother, it can estimate the risk of the most common trisomies from the early stages of pregnancy, with no risk to the fetus. In this article we explain what it measures, from when it can be done and, above all, a distinction worth keeping clear: NIPT is a screening test, not a diagnosis.

What NIPT is and how it works

During pregnancy, small fragments of free fetal DNA (in fact, DNA that comes from the placenta) circulate in the mother's blood. NIPT analyzes this genetic material in a sample of maternal blood and, through sequencing, estimates whether there is an abnormal amount of certain chromosomes. Because it works on a blood sample from the arm, the test does not cross the uterus or the placenta: that is why it is called non-invasive and why it carries no risk to the pregnancy.

NIPT is designed to estimate the risk of the most common aneuploidies:

• Trisomy 21 (Down syndrome).
• Trisomy 18 (Edwards syndrome).
• Trisomy 13 (Patau syndrome).
• Sex chromosome abnormalities, depending on the panel requested.

It is worth keeping in mind what it does not do: NIPT does not detect every genetic condition or structural malformation, and it does not replace the morphology ultrasound. It is one more piece within pregnancy care, complemented by the first-trimester biochemical markers (PAPP-A and free β-hCG) and by imaging studies.

From which week it can be done

NIPT can be performed from week 10 of pregnancy. From that point there is enough free fetal DNA circulating in the maternal blood for the analysis to be representative. Doing it earlier can yield a fetal fraction that is too low and, with it, a less reliable or non-informative result.

Screening, not diagnosis: the key distinction

This is the most important idea in the whole article. NIPT is a very high-performance screening test, but it is not a diagnosis. What does this mean in practice?

• A high-risk result does not, on its own, confirm that the baby has a trisomy. It indicates that it should be confirmed with an invasive test — amniocentesis or chorionic villus sampling — which does offer a definitive diagnosis.
• A low-risk result greatly reduces the probability, but does not bring it to zero.

The CARE study, published in The New England Journal of Medicine, compared cell-free fetal DNA screening against standard screening in a general population of pregnant women and showed that NIPT has a much lower false-positive rate for trisomies 21 and 18.¹ Even so, the recommendation of the scientific societies is categorical: after a positive result, the next step is diagnostic confirmation, not a decision based on screening alone. The American College of Obstetricians and Gynecologists (ACOG) holds that cell-free fetal DNA screening should be offered together with the option of a diagnostic test, and that no screening result, however low or high, is equivalent to a diagnosis.²

NIPT, traditional screening and invasive tests: how they differ

To place NIPT within prenatal care, it helps to compare it with the other two main alternatives: the combined first-trimester screening and invasive diagnostic tests.

Feature	NIPT (fetal DNA)	Traditional combined screening	Invasive test
Type	High-performance screening	Screening	Definitive diagnosis
What it analyzes	Cell-free fetal DNA in maternal blood	PAPP-A and free β-hCG + ultrasound (nuchal translucency)	Cells from amniotic fluid or chorionic villi
From when	Week 10	Weeks 11 to 14	Amniocentesis from week 15; CVS from week 11
Trisomy 21 detection	Very high (close to 99%)	Intermediate	Diagnostic
False positives	Very low (around 0.1%)	Higher	Not applicable (it is diagnostic)
Risk to the pregnancy	None (blood draw)	None (blood + ultrasound)	Risk of pregnancy loss

The takeaway is clear: NIPT combines a very high detection rate with zero risk to the pregnancy, but it remains a screening test. The invasive test is the only one that confirms, and that is why it is reserved for when there is a high-risk result or a specific indication.

Why NIPT changed prenatal care

Before it appeared, many pregnant women with a traditional intermediate-risk screening ended up referred for an invasive test to rule out a trisomy. Because it has a much lower false-positive rate, NIPT makes it possible to reduce the number of unnecessary invasive tests and reserve them for the situations that truly warrant them. The result is more precise monitoring and, for many families, less anxiety, because it narrows the uncertainty at an early stage of pregnancy.

How to get it done at Laboratorio Aclimu

NIPT is a simple blood draw from the arm, with no special preparation. At Laboratorio Aclimu you can have it done as part of our prenatal studies, which form part of the care we provide throughout pregnancy. If you are unsure which test is right for you or at which week to have it, our biochemistry team can guide you. We are located at Marcelo T. de Alvear 2337, Recoleta (Barrio Norte), and you can book your appointment whenever you are ready.

This article was reviewed by the biochemistry team at Laboratorio Aclimu. The information is for general guidance and does not replace a consultation with your doctor or health professional.

Frequently asked questions

What does NIPT detect?

NIPT estimates the risk of the most common trisomies: trisomy 21 (Down syndrome), trisomy 18 (Edwards syndrome) and trisomy 13 (Patau syndrome). Depending on the panel, it can also report on sex chromosome abnormalities. It does not analyze every genetic condition and does not replace the morphology ultrasound.

From which week of pregnancy can it be done?

From week 10 of pregnancy. From that point there is enough free fetal DNA circulating in the mother's blood for the analysis to be reliable. Before week 10 the fetal fraction can be too low, making the result less representative or non-informative.

Is NIPT a definitive diagnosis?

No. NIPT is a high-performance screening test, not a diagnosis. A high-risk result means it should be confirmed with an invasive test (amniocentesis or chorionic villus sampling), which does provide a definitive diagnosis. A low-risk result greatly reduces the probability but does not bring it to zero.

Is it safe for the pregnancy?

Yes. NIPT is performed with a simple blood draw from the mother's arm, so it poses no risk to the fetus. Unlike invasive procedures such as amniocentesis or chorionic villus sampling, it does not cross the uterus or the placenta at any point.

What happens if the result is high-risk?

A high-risk result does not, on its own, confirm that the baby has a trisomy: it must be corroborated with an invasive test. The best course is to discuss the result with your obstetric team and, when appropriate, with genetic counseling, so you can decide the next steps calmly and with complete information.

References

1. Bianchi DW, Parker RL, Wentworth J, et al. DNA Sequencing versus Standard Prenatal Aneuploidy Screening (CARE study). N Engl J Med. 2014;370(9):799–808. Available at: pubmed.ncbi.nlm.nih.gov
2. American College of Obstetricians and Gynecologists. Screening for Fetal Chromosomal Abnormalities: ACOG Practice Bulletin, Number 226. Obstet Gynecol. 2020;136(4):e48–e69. Available at: pubmed.ncbi.nlm.nih.gov · acog.org