Written by Salim Miah MPharm, Independent Prescriber · GPhC 2081653
The question usually arrives on WhatsApp, often late in the evening. Someone has a positive test, a rough idea of their dates and a head full of things they have read online. “How early can I have NIPT? Can I do it at nine weeks? My friend did hers at ten and it came back with no result. Why would that happen?”
I am a prescribing pharmacist, and my wife is a sonographer. Between us we have spent a lot of time thinking about this exact moment in a pregnancy, the stretch between the positive test and the first real answers, when waiting feels harder than it should. So I want to answer it properly, because the honest answer is a little more interesting than “ten weeks”.
The short answer: NIPT can be taken from 10 weeks of pregnancy, but the date only matters because of what it represents: enough placental DNA in your blood for the laboratory to read. Roughly 3 in 100 samples do not give a result first time, usually because that fetal fraction is too low, which is more likely very early in pregnancy or at a higher body weight. A scan before the blood test confirms your dates, the number of babies and that the pregnancy is ongoing, which is why we do one with every NIPT.
What is NIPT actually measuring?
NIPT (non-invasive prenatal testing) is a blood test taken from the mother’s arm. It looks at tiny fragments of DNA floating freely in the bloodstream, known as cell-free DNA. Most of that DNA is yours. According to the NHS Fetal Anomaly Screening Programme handbook, around 90% of the cell-free DNA in a pregnant woman’s blood is maternal and around 10% comes from the placenta.
That second detail is the one people tend to miss. The “baby’s DNA” in an NIPT sample is really placental DNA. In the vast majority of pregnancies the placenta and the baby share the same genetic make-up, so the placenta is a very good stand-in. The laboratory counts DNA fragments from each chromosome, and if chromosome 21, 18 or 13 is slightly over-represented, that raises the chance of Down’s syndrome, Edwards’ syndrome or Patau’s syndrome.
It is a screening test, not a diagnostic one. NIPT gives you a higher-chance or lower-chance result. It cannot tell you for certain that a baby does or does not have a condition. Only a diagnostic test such as CVS or amniocentesis can do that.
Why 10 weeks? Can I have NIPT at 9 weeks?
Placental DNA can be picked up in the mother’s blood from about 5 weeks of pregnancy, the same NHS handbook notes. So why wait?
Because “detectable” and “readable” are not the same thing. In the first weeks the amount of placental DNA is small and it rises as the placenta grows. Laboratories need a minimum proportion, the fetal fraction, before they can call a result with confidence. Ten weeks is the point at which most pregnancies have reached that level reliably, which is why it is the standard starting point. The charity Antenatal Results and Choices (ARC) describes NIPT as available from 10 weeks, and within the NHS the clinical genomics pathway for people with a previous affected pregnancy also uses 10+0 weeks as its minimum, according to NHS England’s GeNotes guidance for clinicians.
There is also a quieter point here. When someone tells me they are “nine and a half weeks”, what they usually mean is nine and a half weeks since their last period. That is an estimate. Cycles vary, ovulation varies, and a pregnancy can easily be a week behind the calendar. If you have NIPT at what you think is ten weeks but is really nine, you are more likely to be in the low fetal fraction zone without knowing it.
So no, we would not take an NIPT sample at nine weeks. And even at ten, I would rather know the dates are right than assume.
Why does NIPT sometimes come back with no result?
This is the part that causes the most worry, so let me be plain about it. A “no result” (sometimes called a no-call or an uninformative result) is not the same as a bad result. It means the laboratory could not get a confident reading from that sample.
It is not rare. ARC estimates that around 3% of samples do not yield enough cell-free DNA for a result. A large laboratory study published in PLoS One in 2024, looking at more than 5,500 pregnancies, found a similar figure: about 3.4% of first samples were uninformative because the fetal fraction was below 5%.
That same study found two things that matter for anyone booking a test. Fetal fraction tended to be lower in women with a higher BMI, and the chance of a failed test fell with each extra week of pregnancy. That is not a judgement about anyone’s body. It is simply arithmetic. A larger blood volume and more maternal cell-free DNA dilute the placental share, so the same placental signal is harder to find.
The common reasons for a no result are:
- Early gestation. The placenta is still small, so its share of the DNA is low.
- Higher maternal weight. More maternal DNA dilutes the placental fraction.
- Sample problems. A tube that is damaged, delayed or underfilled in transit.
- Certain medicines or medical histories. Some treatments and conditions can affect the DNA in the blood, which is why we ask detailed questions before we take a sample.
What happens if my NIPT has no result?
In most cases, a second sample a week or two later gives a result. In the 2024 PLoS One study, just under 60% of women who had a repeat draw after a low fetal fraction then got an informative result. The extra time lets the placenta grow and the fetal fraction rise.
For some, the second sample also fails. The NHS handbook is clear that this can happen, and in the NHS programme the options after a no result are a further NIPT sample, a diagnostic test, or no further testing. That is a reasonable framework privately too. ARC notes that most providers offer a repeat test without extra charge, and it is worth checking that with any clinic before you book.
One honest caveat. A small number of studies have suggested that a persistently low fetal fraction can, in some pregnancies, be associated with a higher chance of certain chromosomal conditions, because some of those pregnancies have smaller placentas. The NHS handbook also cautions that NIPT is less accurate in some situations involving Edwards’ and Patau’s syndromes. So a repeated no result is not something to brush aside. It is a reason to sit down with a clinician and talk about the next step, which might be a detailed scan or referral for diagnostic testing.
Why do we scan before every NIPT?
Every NIPT at our clinic in Bradford includes a pregnancy ultrasound before the blood sample is taken. People sometimes assume that is an upsell. It is not. It is there because a scan answers questions that the blood test silently depends on.
Are the dates right?
A measurement of the baby from head to bottom (the crown-rump length) gives a far more accurate gestational age than counting from a period. If the scan shows you are less far along than you thought, we can wait a few days rather than send a sample with a higher chance of failing. You can read more about what an early scan can and cannot show in our guide to how early a private scan can show a heartbeat.
Is there more than one baby?
Twins change things. NIPT can be used in twin pregnancies, and both the NHS and private laboratories do so, but it is interpreted differently. A higher-chance result means one or both babies may be affected. A 2021 meta-analysis in Ultrasound in Obstetrics & Gynecology on cell-free DNA screening in twins found detection of Down’s syndrome in twins was high, at around 99%, but appeared slightly lower than in singleton pregnancies, and there was not enough data to be confident about Edwards’ and Patau’s syndromes. Twin pregnancies also need a different scan and care pathway, so finding out early matters for reasons well beyond NIPT.
Is there a vanished twin?
This is the one that most people have never heard of. Sometimes a scan shows a second pregnancy sac that is empty, or a second baby that has stopped developing. This is called a vanishing twin, and it is more common in early pregnancy than many realise.
It matters for NIPT because, as the NHS handbook explains, the placenta can continue to shed cell-free DNA even after the baby has died. That leftover DNA can confuse the test and produce a misleading result. For this reason the NHS does not offer NIPT where a vanished twin is seen, and uses other screening approaches instead. Without a scan beforehand, nobody would know to raise it.
Is the pregnancy ongoing?
It is a difficult thing to write, but early pregnancy loss is common. A scan before the blood test means nobody pays for, or waits anxiously on, a screening result for a pregnancy that sadly has not continued. If a scan does show a problem, our team will talk you through it calmly and help you take the right next step with your GP or the early pregnancy unit.
Can NIPT give a false result?
Yes, though it is uncommon. Because the DNA comes from the placenta, a rare situation called confined placental mosaicism can mean the placenta carries a chromosome change that the baby does not. That can produce a higher-chance NIPT result in a healthy baby. NHS England’s GeNotes clinical guidance lists this as a known cause of false positives, alongside the reason every higher-chance result needs confirming with a diagnostic test.
False negatives, where the result is lower chance but the baby is affected, are rarer still, but they do happen. A lower-chance result is very reassuring. It is not a guarantee. Your routine NHS scans, including the anomaly scan at around 20 weeks, still matter.
If you would like to understand what a higher-chance result really means in numbers, I wrote about it in detail in What does a higher-chance NIPT result actually mean?
Who should not have NIPT?
NIPT is not suitable for everyone. The NHS summary information on NIPT lists several situations where it is not appropriate, including:
- triplets or more
- a blood transfusion in the previous four months
- an organ transplant, bone marrow transplant or stem cell therapy
- a current cancer diagnosis, unless in remission
- a vanished twin
The NHS handbook also lists a balanced chromosomal translocation in the mother, or the mother herself having Down’s syndrome or mosaicism for one of the conditions screened. This is exactly why we take a careful history first. As a pharmacist I pay particular attention to medicines and recent treatments, because these are the details people rarely think to mention unless someone asks.
Private NIPT or the NHS route?
In England, the NHS offers NIPT to people whose combined or quadruple test shows a higher chance (between 1 in 2 and 1 in 150). Everyone else is offered the combined test as standard. Private NIPT is a choice some people make to screen earlier or as a first-line test. Neither route replaces your NHS antenatal care, and anyone with a higher-chance private result should be referred into NHS fetal medicine for diagnostic testing and support.
We have covered the differences in more depth in NIPT or the NHS combined test: do you need both?
What I tell people who ask on WhatsApp
I tell them that ten weeks is the starting line, not the finish. If they are unsure of their dates, a scan first will save them time and worry. If they have a higher BMI, I tell them that a no result is more likely but still usually resolved with a second sample, and that it says nothing bad about them. If they are expecting twins, or the scan shows something unexpected, we will slow down and talk it through before any blood is taken.
And I tell them that whatever the result, they will have someone to explain it. That part matters more than the laboratory method.
Our clinic is at Listerhills Science Park in Bradford, a few minutes from the University of Bradford, with free private parking. We see families from across BD postcodes as well as Halifax, Huddersfield, Keighley and Leeds. You can read about our packages and what is included on our NIPT page, or see our full range of pregnancy and baby scans.
Frequently asked questions
How early can I have NIPT?
From 10 weeks of pregnancy. Before that, the amount of placental DNA in your blood is often too low for a reliable result. A dating scan helps confirm you have genuinely reached 10 weeks.
What does “no result” on NIPT mean?
It means the laboratory could not get a confident reading, most often because the fetal fraction was too low. It happens in around 3% of samples and is usually resolved with a repeat sample a week or two later.
Does a higher BMI affect NIPT?
It can. Research shows the fetal fraction tends to be lower at a higher BMI, which makes a no result more likely. Testing a little later in pregnancy can help, and a repeat sample often gives a result.
Can I have NIPT with twins?
Yes. NIPT can be used in twin pregnancies, although it is interpreted differently and appears slightly less sensitive than in single pregnancies. It is not suitable for triplets or more, or where a twin has vanished.
Is NIPT a diagnostic test?
No. NIPT is a screening test that gives a higher-chance or lower-chance result. A higher-chance result should be confirmed with a diagnostic test such as CVS or amniocentesis before any decisions are made.
Why do you scan before taking NIPT blood?
To confirm your dates, check how many babies there are, look for a vanished twin and make sure the pregnancy is ongoing. All of these affect whether NIPT is suitable and how the result should be read.
Sources
- NHS England: Fetal Anomaly Screening Programme handbook, screening for Down’s, Edwards’ and Patau’s syndromes
- NHS England: NIPT for Down’s syndrome, Edwards’ syndrome and Patau’s syndrome, summary information
- NHS England Genomics Education Programme: GeNotes, non-invasive prenatal testing
- Antenatal Results and Choices (ARC): Non-invasive prenatal testing explained
- Gazdarica J et al. Insights into non-informative results from non-invasive prenatal screening. PLoS One, 2024
- Judah H et al. Cell-free DNA testing in screening for trisomies in twin pregnancy: cohort study and meta-analysis. Ultrasound Obstet Gynecol, 2021
Salim Miah MPharm is a GPhC-registered pharmacist and independent prescriber (GPhC 2081653), and the founder of Pulse and Clarity Clinic in Bradford. He graduated from the University of Bradford in 2014 and has worked across community pharmacy, hospital and general practice, where he continues to practise as a prescribing pharmacist. His specialist interests are diabetes and women’s health.