After a miscarriage, the pregnancy's chromosomes can be checked in one of two ways: by reading placental DNA in your blood, or by testing the pregnancy tissue itself. Which is possible for you depends mainly on timing, and on whether any tissue was kept.
In short: before the pregnancy has passed, a blood sample can sometimes be tested. After it has passed, the question becomes whether tissue was collected and kept fresh. Where both can be done, the tissue result is the firmer answer. If you are unsure where you stand, our genetic counsellors can work it out with you.
The basics
Both tests ask the same question: did this pregnancy have a chromosome change, such as an extra or missing chromosome, that could explain why it stopped developing? About half of early miscarriages have a chromosomal cause, usually a chance event. Neither test checks your own chromosomes or your partner's. That needs a separate test, a parental karyotype.
The blood test relies on the placenta. As long as pregnancy tissue remains inside the womb, it sheds tiny fragments of DNA into your bloodstream, often around 5 in every 100 fragments in the sample; the rest are your own. A laboratory counts them chromosome by chromosome, using the same kind of technology as NIPT in ongoing pregnancies, ideally with settings adapted for pregnancy loss.
The tissue test analyses the pregnancy tissue itself once it has come away or been removed, usually the chorionic villi, which are the tiny finger-like parts of the early placenta. On the NHS this means a rapid check for the commonest changes, usually followed by a chromosomal microarray that scans every chromosome for extra or missing material.
The deciding difference is when each sample exists. Placental DNA fades from the blood within hours to days of the tissue passing, while tissue that is collected and kept fresh can be tested afterwards. That is why we always start by asking where things stand for you now.
Your situation
Find the description closest to yours. Each label is a starting point for a conversation with your care team or one of our genetic counsellors, not a decision.
Placental DNA is still circulating, so this is the window for a blood test, ideally before tablets or surgery and after a scan confirms the tissue is still in place. If you will have surgery, or can collect tissue at home, a tissue test can be added.
A blood sample may still work, but fails more often. In a Danish study, about 9 in 100 samples gave no result with tissue still in the womb, against about 27 in 100 drawn 12 to 24 hours after the tissue came away. If you collected the tissue, testing it is usually the stronger option.
The tissue can go to a genetics laboratory, promptly and with no formalin or other preservative. A microarray gives a result in about 9 in 10 suitable samples. See testing pregnancy tissue for how samples are handled.
Unless it passed within about the last day (see the second card), this pregnancy usually can no longer be tested: placental DNA fades from the blood over the following days, and there is nothing to send to a laboratory. What still helps depends on how many losses you have had and whether earlier pregnancies were tested, as explained further down this page.
If a repeat scan is still due, the pregnancy's location is unknown or a molar pregnancy is suspected, genetic testing usually waits until the picture is clear. The largest blood-test study included only confirmed losses inside the womb and excluded molar pregnancies. A scan can also reveal a vanished twin, which can confuse a blood result.
Side by side
Figures come from research studies, mostly of first-trimester losses. A particular laboratory's test may perform differently, so ask any provider for its own figures.
| At a glance | Blood test (cell-free DNA) | Pregnancy tissue test |
|---|---|---|
| Timing | While pregnancy tissue remains in the womb, preferably before treatment. Less reliable from about 12 hours after it passes; in a small Danish group sampled after surgery, about 3 in 10 samples were inconclusive by day 3. | After the tissue has passed or been removed, if it was collected and kept fresh. It should reach the laboratory promptly. |
| Sample | An ordinary blood sample. Often only around 5 in 100 of its DNA fragments come from the placenta. | Pregnancy tissue in a sterile pot, without formalin, sometimes with a sample of your blood as well. |
| What it looks at | Extra or missing whole chromosomes, such as trisomies and monosomy X; in some tests, large missing or extra sections. | A rapid check for common changes, then a microarray of every chromosome, including smaller missing or extra pieces. SNP-based arrays also detect triploidy. |
| What it can miss | Triploidy, with the counting methods used in studies; changes under about 7 million DNA letters (7 Mb) in one study; mosaicism; uniparental disomy; balanced rearrangements; single-gene changes. | Balanced rearrangements; single-gene changes; changes below the array's resolution; some low-level mosaicism. It may also find a change of uncertain meaning. |
| Accuracy | Against tissue, it detected about 78 in 100 chromosome changes (not counting triploidy, which it cannot see) and wrongly flagged about 9 in 100 losses with normal chromosomes (8 studies, 552 miscarriages). | The reference standard that blood-test studies are judged against, provided genuine pregnancy tissue was tested. |
| Common reasons for no result | Too little placental DNA (a low 'fetal fraction'), especially once the tissue has passed. In a Danish study of 1,000 women, 11 in 100 were inconclusive. | No tissue collected, tissue put in formalin, a sample that proves to be maternal tissue, or cells failing to grow for karyotyping (about 1 in 5). |
| Maternal contamination | Most of the DNA is yours by design, and the test allows for it. Rarely, a variation in your own chromosomes is mistaken for the pregnancy's. | Common with karyotyping: about 22 in 100 samples in one study. SNP-based arrays, or comparison with your blood, can detect it. |
| Practicalities | One blood test, ideally just after a scan confirms tissue is still in place and checks for a second sac. Not part of standard NHS care. | Tissue has to be kept: in theatre after surgery, or at home after tablets or waiting. On the NHS, usually offered from the third miscarriage. |
Both tests describe the pregnancy's chromosomes, not yours. Your own are checked only by a separate parental karyotype, when there is a reason to.
Certainty
Testing the tissue reads the pregnancy's own cells, which is why research on the blood test measures it against a tissue result. European guidance (ESHRE) prefers an array-based tissue test to traditional karyotyping, partly because it is less affected by the mother's cells.
The blood test reads a faint signal, and laboratory settings matter. One study found about 82 in 100 changes using thresholds designed for pregnancy loss, but only 55 in 100 with standard NIPT settings. The largest single study, from Copenhagen, reported about 85 in 100, while a smaller UK study by Tommy's researchers found about 6 in 10.
The two kinds of blood result also carry different weight. A 2025 pooled analysis, in which about 6 in 10 losses were chromosomal, estimated that an abnormal result is correct about 93 times in 100, but that around 28 in 100 pregnancies with a normal result still have a chromosome change. A normal blood result lowers the chance of a chromosomal cause without ruling it out.
That does not make the blood test a poor relation when it is the only option. Around one woman in three in the Copenhagen study was unable to collect usable tissue, or collected tissue that was probably her own. When we talk the options through with you, this is the balance we help you weigh.
No sample left
If the pregnancy passed more than a few days ago and no suitable tissue was kept, it can no longer be tested. Many people are in this position, often because nobody mentioned testing at the time. What helps now depends on your history.
Most chromosome changes happen by chance and are not inherited, so no further genetic test is usually needed; UK guidance offers tissue testing from the third miscarriage. If a future pregnancy ends in miscarriage, ask early about keeping tissue or giving a blood sample before treatment. Preparing for your next pregnancy covers this.
You should be offered wider investigations whatever happened with genetic testing, including tests for antiphospholipid syndrome, thyroid tests and a scan of the womb (see recurrent miscarriage). If no tissue could be tested, the RCOG advises offering both partners a chromosome blood test. NHS criteria are narrower, and favour testing the tissue from any future loss.
Earlier results still count. An unbalanced rearrangement in a previous loss is the main reason to offer both partners a parental chromosome test, while a previous trisomy usually points to chance. Keep copies of any reports; our genetic counsellors can go through them with you side by side.
A known chromosome rearrangement in your family, a relative born with an unbalanced chromosome condition, or a previous baby born with congenital abnormalities may justify checking your own chromosomes. European guidance recommends deciding this after an individual assessment of risk.
Next steps
On the NHS, tissue testing is arranged through your early pregnancy unit or a recurrent miscarriage clinic. If you might qualify, say so before treatment, so that tissue is sent fresh. The NHS does not currently provide the blood test as routine care after miscarriage; Tommy's-funded researchers are among those still evaluating it in the UK.
Privately, tissue testing can be arranged after a first or second miscarriage too, provided suitable fresh tissue was kept. With us, it is arranged through a genetic counselling appointment rather than booked online, so that how and when the tissue was collected, and what a result could and could not explain, are talked through before anything is sent.
If you are weighing up a private blood test, check that it was designed and validated for pregnancy loss, and ask who will explain the result. Our genetic counsellors can help you decide whether it is likely to tell you anything useful in your situation, and whether planning for tissue testing instead would serve you better.
Support does not depend on testing. Miscarriage UK and Tommy's both help anyone affected by pregnancy loss, whatever they decide.
How we can help
You can book any of these yourself, without a referral, and your NHS care carries on alongside. London Miscarriage Clinic is part of London Pregnancy Clinic, so booking opens on the London Pregnancy Clinic website. If a treatment date is close, call us or message us on WhatsApp rather than waiting for a reply to the form.
Online, 30 minutes
A video appointment with one of our registered genetic counsellors to work out which sample is realistic for you now, whether any tissue you kept is worth sending, and what a blood or tissue result could and could not explain. Private tissue testing is arranged through this appointment. Partners are welcome to join, and nothing is arranged unless you want it.
Online, 60 minutes
More time when the picture is complicated: a blood result and a tissue result that disagree, reports from more than one pregnancy, three or more losses, or a family history of a chromosome rearrangement. Your counsellor goes through everything with you and explains whether testing either parent would add anything.
Only when indicated
A blood test for one or both parents, looking for a balanced rearrangement. It is mainly advised when a pregnancy's tissue showed an unbalanced rearrangement, or after recurrent miscarriage when no tissue could be tested, so we suggest a counselling appointment first. Results typically take two to three weeks. Testing a couple costs £550.
After repeated losses
Whether or not any pregnancy could be tested, a consultant gynaecologist sees you at our City clinic for a consultation and pelvic scan, with blood tests that include lupus anticoagulant and anticardiolipin antibodies (checks for antiphospholipid syndrome) and a thyroid profile. You book with a £300 deposit, deducted from the package price.
Usually the tissue result, provided the laboratory confirmed it tested the pregnancy's cells rather than yours. Results can differ because the blood test missed a change when little placental DNA was present, because the part of the placenta that releases DNA into the blood carried a change the rest of the pregnancy did not, or because the tissue sample was mostly maternal. One of our genetic counsellors can review both reports with you.
Often the choice is not really between the two. When a miscarriage is managed with tablets or by waiting at home, tissue can be hard to recognise and collect. A blood sample taken before treatment sidesteps that problem, and some people have both: the blood test as a safety net, the tissue if it can be collected.
Usually only if part of it was kept fresh. Tissue for routine examination under the microscope is normally put in formalin, and NHS genetics laboratories class formalin-preserved samples as unsuitable. One large US laboratory obtained results from about 86 in 100 preserved samples, but that is not standard UK practice. If testing matters to you, ask what will be kept before treatment.
It may well be right, but it is worth checking how it was reached. With traditional karyotyping, a normal female result (46,XX) cannot by itself be told apart from the mother's own cells having been tested. Ask whether the laboratory checked for this, for example with a SNP-based microarray or a sample of your blood. If it did, the result is far more reliable.
Not the blood test. Its accuracy has been studied in samples taken before the tissue passed or within a day of it, and in a small Danish group sampled after surgery, about 3 in 10 samples were already inconclusive by day 3. Tissue can sometimes be tested later if it was stored suitably, for example frozen, because a microarray does not need living cells. Tissue that was not kept cannot be tested, and NHS laboratories do not accept tissue kept in formalin.
It can. NHS genetic testing for recurrent miscarriage is built around tissue, and a tissue result showing an unbalanced rearrangement is what usually leads to both partners being tested. A blood result can still inform discussions, but as a screening-type result it is no substitute for tissue that can be collected. Chromosome changes remain common even after repeated losses: European guidance puts them at roughly 4 in 10 tested miscarriages.
No. You can book a genetic counselling appointment yourself, without a GP or hospital referral, and your early pregnancy unit stays in charge of your NHS care. If you can, have any scan reports, treatment dates and earlier genetic results to hand, so the counsellor can see what is still possible. If you are unsure which appointment fits, call us on 020 3687 2939.
This page summarises research and guidance for general information. It is not a diagnosis or a plan for your care; those come from a clinician familiar with your history, whether in your NHS team or ours. Heavy bleeding, severe pain, a raised temperature or feeling faint all need prompt attention from your early pregnancy unit or NHS 111; 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.
