When to Take NIPT: Gestational Age, the 10-Week Rule and Planning the Timing

Prenatal screening guide · 2026

Ten weeks is the earliest, not the optimal. Testing a few days earlier than that is the most common reason a sample has to be repeated.

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

Quick answer

NIPT can be taken from 10 completed weeks of pregnancy. The limit exists because the fetal fraction — the share of circulating cell-free DNA that comes from the placenta — rises with gestation, and below 10 weeks it is too often insufficient to produce a reportable result. Testing at 10 to 12 weeks leaves time for confirmatory chorionic villus sampling if needed. A dating scan first is strongly advisable: it confirms gestational age, confirms a viable single pregnancy, and identifies a twin or vanishing twin, all of which change how NIPT is interpreted.

In this guide

1. Why 10 weeks
2. Planning the window
3. Why the dating scan comes first
4. Other factors that affect timing

Why 10 weeks

Fetal fraction increases steadily through the first trimester as the placenta grows. Below 10 weeks it is frequently under the threshold laboratories require — commonly around 4% — for a reliable call.

A sample taken too early does not usually produce a wrong answer. It produces no answer: a “no result” or “test failure” report requiring a repeat draw, typically one to two weeks later. That means more waiting, at exactly the point in pregnancy when waiting is hardest.

Because gestational age is often uncertain from dates alone, a dating scan before the draw is the simplest way to avoid this. See MedEx imaging services.

Planning the window

The reason to think about confirmation when choosing the NIPT date is simple: if the result comes back high risk, you will want diagnostic testing promptly, and the available procedure depends on gestation. See the prenatal testing pathway guide.

Why the dating scan comes first

A scan before the blood draw does four things NIPT cannot:

• Confirms gestational age, so you are genuinely past 10 weeks rather than relying on an uncertain last menstrual period.
• Confirms viability. NIPT on a non-viable pregnancy produces results that are difficult to interpret.
• Identifies twins, which changes both performance and interpretation — see the guide to NIPT in twins and IVF pregnancies.
• Identifies a vanishing twin, one of the recognised causes of a false positive result.

If a nuchal translucency measurement is being done as part of first trimester screening, that is usually performed between 11 and 14 weeks, and the two can be planned together.

Other factors that affect timing

Maternal weight. Higher maternal weight dilutes the placental DNA fraction, so fetal fraction is lower at any given gestation. Where weight is high, waiting a little longer before testing improves the chance of a reportable result first time.

Certain medications, including low molecular weight heparin, have been associated with lower fetal fraction in some reports. Mention all medicines when booking.

IVF and donor eggs. Gestational dating is usually precise, which helps. Tell the laboratory, since it affects interpretation of some results.

Previous transfusion, transplant or immunotherapy can affect the DNA mixture and should be disclosed.

All of this is more usefully discussed before the draw than after a failed result — a short doctor consultation covers it, and the blood draw itself can be done at home through the nurse-at-home service.

Frequently asked questions

What is the earliest I can have NIPT?

From 10 completed weeks of pregnancy. Before that the fetal fraction is often too low to produce a reportable result, which means a repeat blood draw rather than a wrong answer.

What is the best time to take NIPT?

Between 10 and 13 weeks for most people. That window leaves time for chorionic villus sampling if confirmation is needed, since CVS is usually performed between 10 and 13 weeks.

Do I need a scan before NIPT?

It is strongly advisable. A dating scan confirms gestational age and viability and identifies twins or a vanishing twin, all of which affect how NIPT is interpreted.

Can I have NIPT later in pregnancy?

Yes, NIPT performs well later too, with amniocentesis rather than CVS as the confirmatory option from around 15 weeks. The time available to act on a result narrows as gestation advances.

Does my weight affect when I should test?

Higher maternal weight lowers the fetal fraction at any given gestation. Waiting slightly longer improves the chance of a reportable result on the first sample.

What happens if the test fails?

A repeat blood draw is usually arranged one to two weeks later, by which point the fetal fraction has typically risen. Persistent failure is itself clinically relevant and warrants review.

Sources and further reading

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

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.