Once a miscarriage has been confirmed, and while the pregnancy is still inside the womb, your blood carries tiny fragments of DNA released by the placenta. A laboratory can count them to look for an extra or missing chromosome, one of the commonest reasons an early pregnancy stops developing.
On this page we explain how the test works, why the timing and a scan matter, how often it agrees with tissue testing, what it cannot see, and when a tissue test may suit you better. Having the test is entirely your choice, and our genetic counsellors can help you decide.
Overview
The test is meant for one situation: a scan has confirmed the miscarriage, but the pregnancy has not yet left the womb. That covers a missed miscarriage, an empty pregnancy sac and an incomplete miscarriage where some tissue remains.
It asks whether the pregnancy had a chromosome change, the cause of about half of early miscarriages and usually a matter of chance. It cannot tell you whether a pregnancy is viable, and standard NHS care does not include it: there, genetic testing relies on tissue and usually begins from the third miscarriage.
The science
Blood always contains short fragments of DNA released as cells break down. In pregnancy, some of this cell-free DNA is shed by the placenta's outer layer of cells, the trophoblast.
The placenta and the embryo grow from the same fertilised egg, so they usually share the same chromosomes. Not always: research in ongoing pregnancies finds a chromosome change confined to the placenta (confined placental mosaicism) in about 1 to 2 in 100 placentas, and occasionally the reverse happens. That is one reason the result counts as a strong pointer rather than a final diagnosis.
The laboratory sequences millions of fragments, assigns each to its chromosome and adds up the totals, rather like a census. An extra chromosome shows up as a small surplus; a missing one, as a shortfall.
After a miscarriage, placental DNA is typically only about 5 in every 100 fragments (the fetal fraction); the rest is yours. When that share is very low, a change can be missed or no result given.
NIPT (non-invasive prenatal testing), used during ongoing pregnancies, relies on the same idea. NHS NIPT in England looks only at chromosomes 21, 18 and 13; after a miscarriage, every chromosome needs checking.
Settings matter too. In one study, standard prenatal thresholds detected 55 in 100 of the chromosome changes the tissue showed; thresholds tuned for pregnancy loss detected 82 in 100.
Before the sample
Placental DNA enters your blood only while placental tissue is in place. Once the pregnancy passes or is removed, the supply stops and what is circulating clears: within hours after a birth, more gradually after an early loss. In Danish research involving 1,463 women, about 9 in 100 samples taken with tissue still in the womb gave no result, whereas the failure rate reached about 27 in 100 for blood collected 12 to 24 hours after passing.
A scan shortly before sampling checks that tissue is still present in the womb. It can also reveal a twin or 'vanished twin', whose DNA could confuse the result, or a possible ectopic or molar pregnancy, which the research studies left out. There is no formal guideline on this scan yet; the advice follows how those studies were run.
The miscarriage should already be confirmed by national scan criteria, which can mean a repeat scan; see no heartbeat on scan.
The process
Think through what the result could and could not tell you, and whether you want to be told the pregnancy's chromosomal sex, which a report may include. Deciding against testing is a perfectly reasonable choice, and a genetic counsellor can help you weigh it up.
An ultrasound confirms that tissue is still in the womb. Blood is then drawn from your arm, like any routine blood test.
Waiting, tablets or surgery continue as planned. If you are having surgery, ask about keeping the tissue fresh as a back-up.
The laboratory checks the level of placental DNA, then counts each chromosome. Turnaround varies, so ask in advance, and ideally have a genetics professional, such as one of our genetic counsellors, explain the result to you.
Accuracy
Accuracy is judged against testing of tissue from the same miscarriage. Sensitivity tells you what proportion of the tissue's chromosome changes the blood test also detects; specificity, what proportion of chromosomally normal pregnancies it correctly reports as normal.
A 2025 review of 8 studies (552 miscarriages) found pooled sensitivity of 78 in 100 and specificity of 91 in 100. That leaves out triploidy, which the methods could not see; counting it, sensitivity drops to about 72 in 100. Overall, about 4 in 100 samples gave no result, although one early study reported 27 in 100, particularly in losses before 8 weeks.
Single studies vary: 85 in 100 in an earlier report from the same Danish research, which checked accuracy in 333 women and gave no clear answer for roughly 1 in 9 of all 1,000 women tested, and 59 in 100 in a smaller UK study by Colley and colleagues at Tommy's National Centre for Miscarriage Research. The review's authors judge accuracy after miscarriage to be lower than in ongoing pregnancies, and suited to screening.
In practice
Based on the 2025 review, where about 61 in 100 tested miscarriages had a chromosome change. Figures are rounded and leave out samples with no result. They also leave out triploidy, which the test cannot see, so the true number missed is a little higher.
Detection
For the counting methods used in published miscarriage studies. The middle column is each type's rough share of abnormal tissue results.
| Type of change | Share of abnormal results | Picked up by the blood test? |
|---|---|---|
| Extra copy of one chromosome (trisomy) | The most common, about half to two-thirds | Usually. This is what the test is built to find. |
| One X chromosome instead of two sex chromosomes (monosomy X) | About 11 to 15 in 100 | Can be found, but the result may come from the placenta only, or from some of the mother's cells. |
| Extra whole set of chromosomes (triploidy) | Roughly 1 in 10 to 1 in 5, with the rarer tetraploidy | No, not by counting. Some SNP-based tests, which compare DNA 'spelling' differences, can find certain types, but this has only been shown in a small study of ongoing pregnancies. |
| Large missing or extra piece of a chromosome | About 1 in 20 | Sometimes. One US study missed pieces smaller than about 7 million DNA letters. |
| Small missing or extra piece | Found by microarray in an extra 5 to 7 in every 100 miscarriages | No, they are too small to detect. |
Also not detected: balanced rearrangements (nothing missing or extra), uniparental disomy (both copies of a chromosome from one parent) and single-gene changes. Mosaicism, a mix of normal and abnormal cells, may be missed.
Advantages
In the Danish research, roughly a third of the first 333 women could not provide tissue, or provided a sample that was probably their own. Tommy's adds that, in UK practice, tissue testing is often limited to people who had surgery.
Drawn before the pregnancy passes, the sample leaves you free to wait, take tablets or have surgery for your own reasons.
Collecting tissue at home can be difficult and distressing. A sample taken beforehand does not depend on it.
Tissue sent for testing sometimes turns out to be the mother's own cells. In one US study, the blood test found a trisomy where the tissue result had failed for this reason.
Limitations
Alternatives
Tissue testing, usually by chromosomal microarray, is the benchmark for the blood test and the route the NHS uses. It picks up smaller changes, and SNP-based arrays can also identify triploidy and show whether a sample is really maternal tissue. It may suit you better in these situations.
The two are not either-or: a sample drawn before treatment leaves tissue testing open. Compare them in blood test or tissue test, or see pregnancy tissue testing.
Your options
Diagnosis, treatment and aftercare can stay with your NHS early pregnancy unit, whatever you decide about testing. NHS genetic testing uses tissue, usually from the third miscarriage onwards or after any loss in the second trimester; the blood test is not yet part of it.
A study at Tommy's National Centre for Miscarriage Research, which began in 2021, is comparing blood and tissue results from 350 women with a missed or incomplete miscarriage. The hope is that a validated test could give answers in days rather than the weeks or months tissue results can take.
If you are considering a private test, ask whether the method was validated for pregnancy loss, how often it fails and whether it detects triploidy. We do not currently offer a blood test after miscarriage ourselves.
What we can do is talk it through with you. By video, our genetic counsellors can help you judge whether a blood test fits your circumstances and how it would sit alongside your treatment, and can explain a result once you have one. The appointments are listed in the next section.
Support is also available from Miscarriage UK on 0303 003 6464 and from Tommy's on 0800 0147 800.
How we can help
We work alongside the care your NHS early pregnancy unit provides, and you do not need a referral. Scans take place at our City or West London clinic. London Miscarriage Clinic is part of London Pregnancy Clinic, so booking opens on the London Pregnancy Clinic website. If time is short, call us or send us a WhatsApp message.
Online, 30 minutes
A video appointment with a registered genetic counsellor. Before a sample, it covers whether a blood test is realistic at your stage, how the scan and timing would work, and what an abnormal, normal or failed result would mean. Afterwards, it can help you read the report and decide whether tissue testing or checking parents' chromosomes would add anything. There is also a longer 60-minute appointment.
6–9 weeks · City or West
If the diagnosis is not yet certain, national guidance calls for a repeat scan at least 7 days later. Booked as our viability scan, it is carried out at either clinic by our fetal medicine doctors or specialist sonographers, and you receive a written report. The scan also shows whether pregnancy tissue is still in the womb, which matters if you are thinking about a blood test.
From around 10 weeks · City
If you would like the diagnosis checked before deciding on treatment or testing, Dr Fred Ushakov can carry out an independent scan at our City clinic, form his own view, talk you through what he finds and provide a written report the same day. Your early pregnancy unit continues to manage your care.
Doctor-led, by enquiry
If a result is unexpected or hard to interpret, such as a finding that may come from your own cells, or a missing or extra piece of a chromosome, our Consultant in Clinical Genetics, Dr Harry Leitch, can review the report alongside your history and advise on next steps. In many cases the appointment can be held online. It is arranged by enquiry.
It can be, as research has included losses from about 5 weeks. The chance of no result is higher in very early losses, though, because there is less placental DNA. In the Danish research, a higher level of the pregnancy hormone hCG made a conclusive result more likely.
Yes, so mention it. DNA from a second pregnancy, including a twin that stopped developing earlier (a 'vanished twin'), can mix into the sample and mislead. The scan before sampling helps to spot this.
It depends on the finding. A trisomy usually arises by chance while an egg or sperm is forming, and rarely points to a chromosome problem in either partner. If part of a chromosome appears missing or extra, further tests, sometimes of both parents, may be advised, and any tissue available can confirm the result. See understanding your result; our genetic counsellors can also go through it with you.
Rarely. Most of the DNA in the sample is yours, so a result can occasionally reflect a chromosome difference in some of your own cells, such as cells with a single X chromosome (which become more common with age), or, very rarely, an undiagnosed cancer. A genetics specialist should review any unexpected finding.
Not necessarily. The 2025 review estimated about a 28 in 100 chance of a chromosome change even after a normal result, and some changes are invisible to the test. After recurrent miscarriage, tests for antiphospholipid syndrome and thyroid problems and a scan of the womb's shape are usually advised whatever the result; see recurrent miscarriage.
Yes. You can book an online genetic counselling appointment or a scan yourself, or ring us on 020 3687 2939 if you are unsure which appointment fits. Do keep your early pregnancy unit informed, as they will usually be looking after your treatment and aftercare.
Nothing on this page replaces advice from the people looking after you, and reading it is not a recommendation to have any particular test. Heavy bleeding, strong pain, a temperature or faintness need attention without delay: contact your early pregnancy unit or NHS 111, and in an emergency, dial 999.
Contact
The figures and clinical statements on this page are drawn from the sources below. Guidance evolves — always discuss your individual circumstances with a clinician.
