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Prenatal screening guide · 2026
A low-risk result is genuinely good news about a specific short list of conditions. It is not an all-clear, and the rest of antenatal care is not optional.
A low-risk or negative NIPT result means no increased chance was detected for the conditions on your panel — usually trisomies 21, 18 and 13, and sometimes sex chromosome differences. Because the negative predictive value is very high, this is strongly reassuring for those specific conditions. It does not exclude structural abnormalities, single-gene conditions such as thalassaemia, most chromosomal rearrangements, or pregnancy complications. The anomaly scan at around 18 to 22 weeks remains essential, as does the rest of routine antenatal care.
| What it means | No increased chance detected for the conditions on your panel |
|---|---|
| Reassurance level | Very high negative predictive value for trisomy 21 |
| Does not exclude | Structural abnormalities, single-gene conditions, most rearrangements |
| Still needed | Anomaly scan at 18–22 weeks and routine antenatal care |
| Check the report for | Fetal fraction, and exactly which conditions were screened |
| Counselling | Doctor consultation or specialist teleconsultation before and after testing |
The negative predictive value of NIPT — the chance that a low-risk result is genuinely correct — is very high, particularly for trisomy 21. Unlike positive predictive value, it stays high across age groups, because the conditions are rare and the test is good at clearing unaffected pregnancies.
So a low-risk result is meaningful reassurance. It is one of the few numbers in prenatal screening that is as good as it sounds.
Two things to check on the report before filing it away: the fetal fraction, since a result at the lower end is less robust; and exactly which conditions were screened, since panels differ considerably between laboratories.
| Anomaly scan, 18–22 weeks | Detects structural abnormalities — heart, brain, spine, kidneys, limbs, abdominal wall. NIPT does not assess structure at all. See MedEx imaging services. |
|---|---|
| Carrier screening | Single-gene conditions, especially thalassaemia in the Thai population. See the thalassaemia screening guide. |
| Gestational diabetes screening | Usually 24–28 weeks; unrelated to NIPT. |
| Blood group and antibody screening | Rhesus status and antibodies, with anti-D where indicated. |
| Infection screening | Hepatitis B, syphilis, HIV and rubella immunity as part of routine antenatal care — see MedEx testing services. |
| Growth and wellbeing monitoring | Third trimester assessment of growth, position and placental function. |
Book the anomaly scan — NIPT does not assess structure at all.
False negatives are uncommon but possible. The mechanisms are the same ones that cause false positives: confined placental mosaicism, where the placenta does not reflect the fetus; and low fetal fraction, which reduces the ability to detect a difference.
The practical implication is not to distrust a low-risk result, but to keep taking ultrasound findings seriously. If a scan later shows a structural abnormality or soft markers, that finding is not overruled by the earlier NIPT — it should be investigated on its own merits, potentially with diagnostic testing and chromosomal microarray.
Put simply: NIPT and ultrasound answer different questions, and a good answer to one does not settle the other.
A short doctor consultation after the result is a useful point to plan the rest of the pregnancy rather than to interpret a single report.
It means no increased chance was detected for the conditions on your panel, usually trisomies 21, 18 and 13. It does not exclude structural abnormalities, single-gene conditions or pregnancy complications, so the anomaly scan and routine antenatal care remain essential.
The negative predictive value is very high, particularly for trisomy 21, and it stays high across age groups. It is one of the few figures in prenatal screening that is as good as it sounds.
Yes. NIPT does not assess structure at all, so the 18 to 22 week anomaly scan covers entirely different ground – heart, brain, spine, kidneys, limbs and abdominal wall.
Uncommonly. The causes are confined placental mosaicism, where the placenta does not reflect the fetus, and low fetal fraction. This is why a later ultrasound finding should be investigated on its own merits rather than dismissed.
It is worth considering, particularly in Thailand where thalassaemia carriage is common, and for anyone with a family history of a genetic condition. Carrier screening is entirely separate from NIPT.
The fetal fraction, since a low value makes the result less robust, and exactly which conditions were screened, since panels differ considerably between laboratories.
Carrier screening is a separate question, and an important one in Thailand.
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.
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