NIPT in Bangkok: What It Is, When to Take It, and Where Its Limits Are

Prenatal screening guide — start here · 2026

NIPT is the most accurate prenatal screening test available, and it is still a screening test. Understanding that distinction is most of what you need.

By MedEx · Updated September 2026 · Approx. 10-minute read

Quick answer

Non-invasive prenatal testing (NIPT) analyses cell-free DNA circulating in the mother’s blood, most of which comes from the placenta. From 10 weeks of pregnancy onwards it can screen for the common trisomies — Down syndrome (trisomy 21), Edwards syndrome (trisomy 18) and Patau syndrome (trisomy 13) — and for sex chromosome differences. It requires only a maternal blood sample, so it carries no risk of miscarriage. But it remains a screening test: a high-risk result estimates probability and must be confirmed by chorionic villus sampling or amniocentesis before any decision is made.

In this guide

1. How NIPT works
2. What it screens for
3. What NIPT cannot tell you
4. Accuracy, honestly stated
5. Who should consider it, and what comes next

How NIPT works

During pregnancy, small fragments of DNA from the placenta circulate in the mother’s bloodstream alongside her own. NIPT sequences this mixture and measures whether the amount of DNA from each chromosome is what would be expected. An excess of chromosome 21 material, for example, suggests a higher chance of trisomy 21.

The proportion of the total that comes from the placenta is called the fetal fraction. It matters because the test needs enough placental DNA to detect a difference reliably — typically at least around 4%. Fetal fraction rises with gestational age and falls with higher maternal weight, which is why timing and, occasionally, a repeat sample matter. This is covered in detail in the fetal fraction guide.

The important nuance: the DNA comes from the placenta, not directly from the baby. Usually they are genetically identical, but not always — and that is the origin of most false positives.

What it screens for

Panels vary considerably between laboratories, so check what is actually included before booking through the MedEx NIPT service.

What NIPT cannot tell you

This is where expectations most often diverge from reality. NIPT does not screen for:

• Most structural abnormalities — heart defects, cleft lip and palate, limb differences, kidney anomalies. These are found on ultrasound, which is why the anomaly scan remains essential. See MedEx imaging services.
• Neural tube defects such as spina bifida.
• Single-gene conditions such as thalassaemia, cystic fibrosis or spinal muscular atrophy. These need carrier screening — particularly relevant in Thailand, where thalassaemia carriage is common. See the thalassaemia carrier screening guide.
• Most chromosomal rearrangements, including balanced translocations and many copy number changes.
• Developmental outcome. A low-risk NIPT is not a guarantee of a healthy baby.

A low-risk NIPT combined with a normal anomaly scan is reassuring. Neither alone is complete.

Accuracy, honestly stated

NIPT is frequently marketed as “99% accurate”, which conflates two different measures.

Sensitivity — the proportion of affected pregnancies the test flags — is genuinely above 99% for trisomy 21. That number is real.

Positive predictive value — the chance that a high-risk result actually reflects an affected pregnancy — is a different figure entirely, and it depends on how common the condition is in the population being tested. Because trisomy 21 is uncommon, particularly in younger mothers, the positive predictive value can be considerably lower than 99%. For rarer conditions such as trisomy 13 and for microdeletions, it can be low enough that most positive results are false.

The practical consequence: no irreversible decision should ever be made on a NIPT result alone. Confirmatory diagnostic testing is required. The arithmetic is explained in the NIPT accuracy guide.

Who should consider it, and what comes next

NIPT is appropriate for anyone who wants information about the common trisomies without procedural risk. It is particularly useful with advanced maternal age, a higher-risk first trimester combined screening result, or a previous affected pregnancy — and in the last two situations the positive predictive value is higher because the prior risk is higher.

Before testing, it is worth deciding what you would do with each possible result. Some people want the information regardless; others would not act on it and may prefer to decline. Both are reasonable, and a short conversation before the blood draw is more valuable than one afterwards. Book a doctor consultation or specialist teleconsultation.

After the result: a low-risk report still needs the routine anomaly scan; a high-risk report needs confirmatory testing before anything else. See the high-risk result guide and the prenatal testing pathway guide for how the options fit together.

Frequently asked questions

When can NIPT be done?

From 10 completed weeks of pregnancy. Testing earlier risks an insufficient fetal fraction and a result that cannot be reported, which usually means repeating the blood draw.

Is NIPT a diagnostic test?

No. It is a screening test that estimates probability. A high-risk result must be confirmed by chorionic villus sampling or amniocentesis before any decision is made.

Is NIPT safe for the baby?

Yes. It requires only a blood sample from the mother and carries no risk of miscarriage, unlike invasive diagnostic procedures.

What does NIPT not detect?

Most structural abnormalities such as heart defects, neural tube defects, single-gene conditions such as thalassaemia and cystic fibrosis, and most chromosomal rearrangements. The anomaly scan and carrier screening cover different ground.

Is NIPT really 99 percent accurate?

Sensitivity for trisomy 21 is genuinely above 99 percent, but that is a different measure from the chance that a positive result is correct. Positive predictive value depends on how common the condition is and can be considerably lower, especially for rarer conditions.

Do I still need an ultrasound if NIPT is low risk?

Yes. NIPT does not assess structure, so the anomaly scan remains essential regardless of the NIPT result.

Sources and further reading

1. MedEx NIPT service
2. ACOG Practice Bulletin: Screening for Fetal Chromosomal Abnormalities
3. ACMG: Noninvasive prenatal screening practice resource
4. ISPD position statement on cell-free DNA screening

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.