NIPT Eligibility & Timing
Check whether you're eligible for non-invasive prenatal testing — and exactly when to book. NIPT is valid from 10 weeks; some pregnancies need to meet additional criteria.
Can I have NIPT yet?
Answer three quick questions. Get an instant eligibility check.
Cycle length adjustment
Your eligibility checklist
Here's how your pregnancy measures against each criterion.
Confirm your dates with a dating scan
NIPT interpretation depends on accurate gestational age. A dating scan confirms it to within 3–5 days — and is often bundled with the NIPT appointment.
What NIPT actually does
Non-invasive prenatal testing (NIPT) is a blood test that screens for the most common chromosomal conditions in your baby. It works by analysing fragments of cell-free fetal DNA that circulate in your bloodstream during pregnancy — tiny pieces of placental DNA that give a remarkably accurate picture of your baby's chromosomes without any invasive procedure.
NIPT becomes valid from 10 weeks of pregnancy because before then, there isn't enough fetal DNA in your blood for the test to produce a reliable result. The clinical term for this is "fetal fraction" — the percentage of cell-free DNA in your sample that came from the placenta. A fetal fraction below 4% produces an inconclusive result, and this is more common in early pregnancy, in twin pregnancies, and where maternal BMI is higher.
The test screens primarily for Down's syndrome (trisomy 21), Edwards' syndrome (trisomy 18) and Patau's syndrome (trisomy 13). Many NIPT packages also include sex chromosome conditions (Turner, Klinefelter) and microdeletions. Detection rates are exceptionally high — above 99% for Down's syndrome — which is why NIPT has largely replaced older screening tests.
Screening, not diagnosis
NIPT is a highly accurate screening test — but it's not diagnostic. A "high risk" or "positive" result means your baby has a higher chance of having one of the tested conditions, not a certainty.
A positive result is followed up with a diagnostic test like chorionic villus sampling (CVS) or amniocentesis, which are definitive but carry a small procedure-related risk.
Conditions NIPT screens for
All three trisomies are covered as standard. Extended panels add sex chromosome conditions and selected microdeletions.
Down's syndrome
Trisomy 21 — an extra copy of chromosome 21. The most common chromosomal condition. NIPT detection rate is above 99%.
Edwards' syndrome
Trisomy 18 — an extra copy of chromosome 18. A serious condition with high perinatal mortality. Detection rate above 97%.
Patau's syndrome
Trisomy 13 — an extra copy of chromosome 13. Another serious condition with severe developmental effects. Detection rate around 87%.
Sex chromosome conditions
Optional extended panel. Includes Turner (X0), Klinefelter (XXY), Triple X (XXX) and Jacobs' (XYY) syndromes.
Microdeletions
Optional. Rare but serious conditions like DiGeorge (22q11) syndrome. Not included in all NIPT packages.
Fetal sex
If you want to know, NIPT reveals your baby's sex with very high accuracy — available from 10 weeks, earlier than any ultrasound.
NIPT timing at a glance
Key dates and eligibility rules applied by the calculator above.
| Situation | Earliest | Notes |
|---|---|---|
| Singleton pregnancy | 10 weeks | No upper limit — valid throughout pregnancy |
| Dichorionic twins | 10 weeks | Works well; combined DNA from two placentas |
| Monochorionic twins | 10 weeks | Genetically identical — standard NIPT works |
| Triplets or higher | Not validated | Standard NIPT isn't validated for triplets or more |
| Donor egg pregnancy | 10 weeks | Standard panels work; sex chromosome reporting may vary |
| Before 10 weeks | — | Fetal fraction too low; test produces inconclusive results |
Why dating matters for NIPT
Your gestational age affects whether NIPT will work — and how confident you can be in the result.
Frequently asked questions
Why does NIPT only work from 10 weeks?
Before 10 weeks, there usually isn't enough fetal DNA circulating in your bloodstream for the test to work reliably. The technical measure is "fetal fraction" — the percentage of the DNA in your sample that came from the placenta. Below about 4%, the laboratory can't produce an accurate result. Fetal fraction rises steadily through pregnancy, reaching levels that support testing by 10 weeks.
Is NIPT better than the combined test?
For Down's syndrome detection, yes. NIPT detects over 99% of cases with a false positive rate below 0.1%. The combined test (NHS first-trimester screening) detects around 85% with a 5% false positive rate. NIPT is more accurate and produces far fewer "high risk" results that turn out to be false alarms on amniocentesis.
What if my NIPT comes back "inconclusive"?
It happens in roughly 1–3% of cases, usually due to low fetal fraction. The laboratory will redraw another blood sample, often two weeks later when fetal fraction has risen. If repeat samples remain inconclusive, your sonographer will discuss alternatives — usually a detailed ultrasound assessment, or direct CVS/amniocentesis if indicated.
Does NIPT work for IVF pregnancies?
Yes. Standard NIPT works for own-egg IVF pregnancies exactly as it does for naturally conceived ones. For donor egg pregnancies, some sex chromosome reporting may be limited because the baby's DNA isn't related to the carrier's — but trisomy detection (Down's, Edwards', Patau's) remains fully valid.
Can I have NIPT if I'm carrying twins?
Yes, from 10 weeks, for both dichorionic (non-identical) and monochorionic (identical) twins. Detection rates are slightly lower than for singletons because fetal fraction is shared between two babies, and results apply to both babies together — NIPT can't tell which twin a positive result comes from. For triplets or higher, standard NIPT isn't validated and alternative approaches are needed.
Can NIPT tell me the sex of my baby?
Yes, with very high accuracy — and earlier than any ultrasound. Sex determination is valid from 10 weeks, roughly six weeks before the earliest gender scan. For twin pregnancies, NIPT can tell whether you're carrying any Y chromosome — so it can confirm "at least one boy" but can't distinguish between twin A and twin B.
How long do NIPT results take?
Results usually arrive 5–10 working days after the blood sample is taken, depending on the laboratory. Some clinics offer expedited pathways with 3–5 day turnaround. Your sonographer will contact you once the lab report is available, and offer a consultation if the result needs to be discussed in detail.
Book your NIPT at IUS London
Non-invasive prenatal testing from 10 weeks, with dating scan included. Results within 5–10 working days. Same-week appointments at our Kensington clinic.