NIPT vs First Trimester Combined Screening: Which One, and Why Not Both?

Prenatal screening guide · 2026

NIPT outperforms combined screening at detecting trisomies. The nuchal translucency scan still earns its place, for reasons that have nothing to do with trisomies.

By MedEx · Updated September 2026 · Approx. 8-minute read

Quick answer

First trimester combined screening uses maternal age, a nuchal translucency measurement on ultrasound, and two blood markers (PAPP-A and free beta-hCG) to estimate risk. It detects around 85–90% of trisomy 21 cases with a false positive rate of roughly 5%. NIPT detects over 99% with a far lower false positive rate, so for trisomy detection it is clearly superior. But the nuchal translucency scan contributes information NIPT does not: an increased measurement is associated with cardiac defects and other conditions even when chromosomes are normal, and PAPP-A relates to placental function and later pregnancy risk.

In this guide

1. Where NIPT clearly wins
2. What the nuchal translucency scan still adds
3. The biochemistry has a second life
4. A sensible combined approach

Where NIPT clearly wins

For detecting the common trisomies, the comparison is not close. Combined screening flags roughly 85 to 90% of trisomy 21 cases while producing a false positive rate around 5% — meaning one in twenty women screened is told they are high risk, and the great majority of those pregnancies are unaffected.

NIPT detects over 99% with a false positive rate well under 1%. Introducing it into screening programmes has substantially reduced the number of invasive diagnostic procedures performed, which is a genuine benefit rather than a marketing claim.

If your question is specifically about trisomy 21, 18 or 13, NIPT is the better test. See the NIPT guide.

What the nuchal translucency scan still adds

The NT measurement is not merely a less accurate way of screening for Down syndrome. An increased nuchal translucency, even with normal chromosomes, is associated with:

• Congenital heart defects, which are among the most common serious birth anomalies and which NIPT cannot detect at all.
• Skeletal dysplasias and other genetic syndromes, many outside any NIPT panel.
• Certain single-gene conditions, such as Noonan syndrome, which may prompt specific further testing.

So an increased NT with a low-risk NIPT is not reassuring — it warrants a detailed cardiac assessment and often diagnostic testing with chromosomal microarray. Anyone told their NIPT was normal and therefore the NT does not matter has been misinformed.

The scan also confirms dating, viability, number of fetuses and chorionicity — all of which affect NIPT interpretation. See MedEx imaging services.

The biochemistry has a second life

PAPP-A and free beta-hCG were introduced for trisomy screening, but they carry information about placental function.

A low PAPP-A, even with normal chromosomes, is associated with an increased risk of fetal growth restriction, pre-eclampsia, preterm birth and stillbirth. In many units it triggers additional growth surveillance in the third trimester and, in some protocols, consideration of aspirin prophylaxis where other risk factors are present.

That is a genuinely useful output that NIPT does not provide. It is one reason some units continue to offer biochemistry alongside NIPT rather than replacing it.

A sensible combined approach

The pragmatic pathway used in many settings:

1. Dating scan to confirm gestation, viability and number of fetuses.
2. NIPT from 10 weeks for trisomy screening — the more accurate option.
3. Nuchal translucency scan at 11–14 weeks, for its independent structural and cardiac information rather than for trisomy risk.
4. PAPP-A where the unit uses it for placental risk stratification.
5. Anomaly scan at 18–22 weeks, which remains essential regardless of everything above.
6. Carrier screening where relevant — particularly thalassaemia in Thailand.

Cost and availability vary, so this is a conversation to have with your obstetric team early. A specialist teleconsultation can help you decide what is worth doing in your circumstances, and the full sequence is set out in the prenatal testing pathway guide.

Frequently asked questions

Is NIPT better than combined screening?

For detecting trisomies 21, 18 and 13, clearly yes – above 99 percent detection with a far lower false positive rate, compared with around 85 to 90 percent detection and roughly 5 percent false positives for combined screening.

Do I still need a nuchal translucency scan if I have NIPT?

The NT scan provides information NIPT cannot. An increased measurement is associated with cardiac defects and other syndromes even when chromosomes are normal, so a low-risk NIPT does not make an increased NT reassuring.

What does PAPP-A tell me?

Beyond trisomy screening, a low PAPP-A is associated with increased risk of fetal growth restriction, pre-eclampsia, preterm birth and stillbirth, and may trigger additional growth surveillance later in pregnancy.

Can I have both NIPT and combined screening?

Yes, and many units offer NIPT for trisomy screening alongside the nuchal translucency scan and biochemistry for their independent information. Cost and availability vary.

What if my NT is increased but NIPT is low risk?

This warrants detailed cardiac assessment and often diagnostic testing with chromosomal microarray. The NIPT result does not overrule the ultrasound finding.

When is combined screening done?

Between 11 and 14 weeks, since the nuchal translucency measurement is only valid within that window.

Sources and further reading

1. ACOG Practice Bulletin: Screening for Fetal Chromosomal Abnormalities
2. ISUOG practice guidelines: first trimester fetal ultrasound
3. MedEx imaging services

Medical disclaimer: This article is general health information and does not replace medical advice, diagnosis or treatment. Laboratory reference ranges differ between laboratories and results must be interpreted alongside your symptoms, medicines and medical history. Speak with a qualified clinician before starting, stopping or changing any treatment. Service details, inclusions and prices can change — confirm them with MedEx before booking.