A small sample of your blood contains tiny pieces of your baby's DNA. NIPT reads that DNA to look for extra or missing chromosomes.
NIPT is a screening test — not a final answer. A "positive" result always needs a diagnostic test (amniocentesis or CVS) to confirm.
Think of sensitivity like a fishing net. If the baby truly has a chromosomal condition, this net is so fine that it will catch it and sound the alarm over 99% of the time.
Specificity is how well the test avoids a false alarm. If your baby does not have a chromosomal condition, the test will correctly stay quiet 99.9% of the time.
A test can be 99% accurate at finding the condition AND still have a positive result that is wrong most of the time — especially when the condition is very rare.
A smoke detector is very sensitive — it catches almost every real fire. But in a kitchen, it also goes off when you make toast. The alarm ringing does not mean the house is on fire. That is why we need PPV — to know how often the alarm means a real fire.
PPV asks: "Since the alarm is ringing, what are the actual chances there is a fire?" Because some conditions are rare, a positive result may only mean a 20–50% actual chance the baby is affected. A diagnostic test is always needed to confirm.
| Condition | Sensitivity | Specificity | PPV Range |
|---|---|---|---|
| Trisomy 21 Down Syndrome |
99–100% | 99.9% | 70–91% |
| Trisomy 18 | 98–100% | 99.7–99.9% | 47–68% |
| Trisomy 13 (Rarest of the three) |
98–100% | 99.7–99.9% | 10–28% |
Even though the test is nearly 100% sensitive, a positive for Trisomy 13 may be wrong 7 out of 10 times — because the condition itself is very rare. Always confirm with diagnostic testing.
NPV is our peace of mind number. If your test comes back "negative" or "low-risk", the chance that your baby does not have these specific chromosomal conditions is greater than 99.9%. You can feel highly reassured.
| Term | Simple Question It Answers | NIPT Result | Color Code |
|---|---|---|---|
| Sensitivity | Does the test find the condition if it's there? | >99% | Excellent |
| Specificity | Does the test stay quiet if the baby is fine? | 99.9% | Excellent |
| PPV | If positive, how likely is the baby truly affected? | 10–91% (varies) | Confirm Always |
| NPV | If negative, how reassured can I be? | >99.9% | Highly Reassuring |
Do not panic. This is a screening result only.
Your doctor will discuss diagnostic testing (amniocentesis or CVS) to get a definitive answer.
Genetic counseling will be offered.
You can feel highly reassured.
The chance your baby has one of these conditions is less than 1 in 1,000.
Continue routine prenatal care.
These numbers can feel confusing. That is completely normal.
We will walk you through every result, answer every question, and help you make the best decisions for you and your baby.