Miscarriage is common
Around 15 of every 100 known pregnancies end in miscarriage. You are far from alone.
Miscarriage: Can We Understand Why It Happened?
A miscarriage often happens by chance, for reasons outside anyone's control, yet the question of why can stay with you for a long time. This guide explains the known causes, which genetic tests exist, what the NHS offers and why timing matters, and where our genetic counsellors and fetal medicine team can help.
About half of early miscarriages happen because of a chromosome difference in the pregnancy, usually one that arose by chance. Testing cannot always find a cause, but when it does, it can replace self-blame with an explanation and help you plan what comes next.
Is the pregnancy still in the womb?
If a scan has confirmed a miscarriage but the pregnancy has not yet come away, and you have not had tablets or a procedure, some testing choices are time-sensitive. While pregnancy tissue remains in the womb, placental DNA is still in your blood, so a blood-based test may be possible. To have the tissue itself tested, ask your early pregnancy unit before treatment: it must be sent fresh, not in formalin. Read testing before a miscarriage completes. A test should never delay care you need.
Start here
Looking for a reason is natural
After a miscarriage, nearly everyone asks why. Often the honest answer is chance: an extra, missing or rearranged chromosome that arose as the egg or sperm formed, or in the first cell divisions. In most cases this is a one-off event, and it was not caused by anything either parent did.
Genetic testing looks at the chromosomes of the pregnancy itself, using pregnancy tissue or, in some situations, a blood sample taken while pregnancy tissue remains in the womb. A result can explain a loss, show whether the parents' own chromosomes need checking, and inform plans for another pregnancy. It cannot always find a cause.
This page maps all our guides on miscarriage and genetics. Begin with whichever question feels most pressing, or go straight to What can I test now? to see which tests fit your situation.
The essentials
Six things worth knowing
The rest of this guide builds on these six points. Each card links to the page that explains it in more depth.
Chromosomes are the most common known cause
Around half of early miscarriages are caused by a chromosome change in the pregnancy: too many, too few or a rearranged chromosome. The parents' own chromosomes are usually normal.
Age plays a part
As eggs get older, more of them carry chromosome errors, so miscarriage becomes more likely, especially from the late 30s. It still happens at every age.
Testing may explain why
About 6 in 10 miscarriages that are tested show a chromosome abnormality. A normal chromosome result leaves other causes possible, so no test can promise an answer.
Where the pregnancy is now matters
Your options depend on timing: the pregnancy may still be inside the womb, it may have passed with tissue saved, or no tissue may have been collected.
Timing matters
Placental DNA in your blood falls once the pregnancy has passed, and tissue must reach the laboratory fresh. Asking before treatment keeps more options open.
The numbers behind miscarriage
These are figures for large groups of people, not predictions for any one pregnancy. Age estimates vary. The RCOG patient leaflet gives around 1 in 4 at 35 to 39 and around 1 in 2 at 40 to 44, figures that match a large Danish study of pregnancies from 1978 to 1992. Newer pooled data, shown below, give lower figures, probably because the studies differ in country, decade and how losses were counted. Our statistics guide compares them.
About 15 in 100 Share of recognised pregnancies ending in miscarriage when many studies are pooled (Lancet 2021, Quenby et al.). The RCOG estimates up to 1 in 5 in the first three months.
About 1 in 2 Miscarriages that happen because the pregnancy developed with abnormal chromosomes (RCOG patient information, 2023)
12 vs 37 in 100 Miscarriage risk for women aged 20 to 29 compared with women aged 40 to 44, in pooled data (Quenby et al., Lancet 2021)
3 to 6 in 100 Couples with recurrent miscarriage in whom one partner carries a balanced chromosome rearrangement (RCOG patient information, 2023; NICE CKS)
Your path through this guide
Seven questions, in the order most people ask them
Something has happened
Bleeding has led to a miscarriage, or a scan shows the pregnancy has stopped developing, sometimes confirmed only on a repeat scan. Your early pregnancy unit explains the options for care.
Why did it happen?
Often a chance chromosome difference in the pregnancy, though other causes exist and sometimes none is found.
Can it be investigated?
Often, yes: from pregnancy tissue, or in some situations from a blood sample taken before the pregnancy has passed.
Which test is possible now?
It comes down to timing and history: where the pregnancy is now, whether tissue was kept fresh, and how many losses you have had.
What does the result mean?
A whole chromosome too many or too few, a small piece lost or gained, or a normal result: each points to different next steps.
Could it happen again?
After a chance chromosome difference, the outlook for the next pregnancy is generally better than after a loss with normal chromosomes at the same age. Repeated losses or a parental rearrangement need specialist advice.
What about the next pregnancy?
Planning can include reviewing earlier results, an early scan, and choices about screening such as NIPT or diagnostic testing.
Guides
Just diagnosed
For the first days after a scan finding or a miscarriage: what the words mean, and what you can still decide.
Just been diagnosed
What to do in the first days, and the question to ask before any treatment.
Missed miscarriage
When a pregnancy stops developing without symptoms, how it is confirmed and the choices that follow.
No heartbeat on the scan
What the finding can mean at different stages, and when a repeat scan is needed first.
Pregnancy stopped growing
Why development can stop, and how often chromosomes are involved.
Empty sac (blighted ovum)
A pregnancy sac without an embryo: what the term means and whether testing is possible.
Testing before treatment
Why some tests need to happen before the pregnancy passes or is treated.
Guides
Why it happened
The causes of miscarriage, the chromosome changes involved and the numbers behind them.
Why did I miscarry?
Whether knowing the cause matters, and the everyday things people worry about.
Chromosomal and genetic causes
Extra or missing chromosomes, lost or gained segments, and which changes can run in families.
Miscarriage statistics
The figures for frequency and age, and why different studies reach different numbers.
Guides
Genetic testing
Which tests exist, how they differ and how to read the result.
What can I test now?
A step-by-step guide to the test that fits your situation today.
Blood-based genetic testing
How placental DNA in the mother's blood can be analysed after a miscarriage is diagnosed, and its limits.
Pregnancy tissue testing
Chromosome testing of tissue after a miscarriage, and how samples should be handled.
Blood test or tissue test?
The two approaches side by side, and which may be possible for you.
Parental karyotype
When testing the parents' chromosomes helps, and when it is not needed.
Understanding your result
What trisomy, monosomy, a missing piece or a normal result means for you.
Guides
Recurrent miscarriage
When pregnancy loss happens more than once.
Recurrent miscarriage
Genetic testing alongside the wider investigations, including antiphospholipid syndrome, thyroid tests and the shape of the womb, plus our recurrent miscarriage tests.
Guides
Next pregnancy
Planning ahead, at your own pace.
Preparing for your next pregnancy
Results to gather, health checks before trying again and planning an early scan.
After a chromosomal miscarriage
Genetics advice, early scans, NIPT and diagnostic testing in the pregnancy that follows.
NHS and private care
What the NHS offers, and where private testing fits
Your NHS early pregnancy unit assesses bleeding and pain in early pregnancy free of charge, confirms a miscarriage on scan and looks after treatment. NICE recommends waiting 7 to 14 days for the pregnancy to pass naturally as the usual first option, with tablets or a procedure offered when that is unsuitable or not what you want.
NHS genetic testing follows national criteria. The RCOG recommends offering chromosome testing of pregnancy tissue from the third miscarriage onwards and after any miscarriage in the second trimester. In England, tissue from a third or later miscarriage is tested for the commonest chromosome changes and with a chromosomal microarray, which looks across all the chromosomes. A single miscarriage can also be tested when there are features that suggest a chromosome condition.
In the UK, recurrent miscarriage means three or more miscarriages, although doctors may investigate after two if they suspect an underlying cause; European guidance uses two. Roughly 1 woman in 100 has three or more miscarriages. Recurrent miscarriage clinics check for antiphospholipid syndrome, thyroid problems and the shape of the womb, and test the parents' chromosomes only when tissue shows an unbalanced rearrangement or could not be tested.
Many people would like answers sooner, after a first or second miscarriage. European guidance for people who have had two or more losses says testing pregnancy tissue is not routinely needed but can be done to help explain a loss. NHS testing uses tissue rather than blood. Private testing suits some people and not others, and a genetic counsellor can help you weigh what a result could change.
London Pregnancy Clinic
How we can help
We are a private clinic with sites in the City of London and in West London. Our miscarriage care page covers scans, aftercare and emotional support; the services below are the ones most relevant to genetic questions. NHS care remains available alongside any of them.
Online, by video
Genetic counselling
A 30-minute appointment with a registered genetic counsellor, through our partner Jeen Health, to talk through what can be tested now, what a result might mean and how pregnancy tissue testing is arranged. A 60-minute appointment (£140) suits more complex histories.
If a finding is unclear
Second-opinion scan
From around 10 weeks, a detailed scan with Dr Fred Ushakov if a scan finding is uncertain or you would like another specialist view before deciding on treatment.
Parents' chromosomes
Karyotype test
A blood test of one or both partners' chromosomes, arranged with Jeen Health, used when pregnancy tissue has shown an unbalanced rearrangement, or when tissue could not be tested. £290 for one person or £550 for a couple.
After repeated losses
Recurrent miscarriage tests
A consultant gynaecologist consultation and pelvic scan, with blood tests including lupus anticoagulant, anticardiolipin antibodies and a thyroid profile. You book with a £300 deposit, which is deducted from the total.
After your first period
Post-miscarriage scan
A recovery scan and review, usually after your first period, to check the womb has returned to normal and look for any remaining pregnancy tissue. It is not a scan for diagnosing a miscarriage.
Doctor-led genetics
Clinical genetics consultation
For complex or unexpected results, a known chromosome rearrangement in the family, or detailed planning for a future pregnancy, with Dr Harry Leitch, Consultant in Clinical Genetics. Enquire to book.
Miscarriage and genetic testing: your questions
Will genetic testing definitely tell us why the miscarriage happened?
No test can promise an answer. Testing the pregnancy can find a chromosome difference when there is one. When none is found, the cause may lie elsewhere or remain unknown, because a normal chromosome result does not rule out other causes in the pregnancy or in the mother.
A genetic counselling appointment before testing can help you decide whether it is worthwhile for you.
Is genetic testing available on the NHS after a first miscarriage?
Not usually. The RCOG recommends offering chromosome testing of pregnancy tissue from the third miscarriage onwards and after any second-trimester miscarriage. In England, a single miscarriage can be tested on the NHS when there are features suggesting a chromosome condition.
Outside those situations, testing is a private choice. European guidance for people who have had two or more losses says tissue testing is not routinely needed but can be done to help explain a loss.
If the pregnancy had a chromosome problem, does one of us carry a genetic condition?
Usually not. Most chromosome differences found after a miscarriage happen by chance while the egg or sperm is forming, and the parents' own chromosomes are normal. Occasionally one partner carries a balanced rearrangement that causes them no health problems; this is found in around 3 to 6 in 100 couples who have had recurrent miscarriages.
Testing the parents is offered when tissue shows an unbalanced rearrangement or could not be tested. Our guide to parental karyotype after miscarriage explains when it helps.
Why does it matter whether the pregnancy has passed yet?
Two kinds of sample can be tested. While pregnancy tissue is still in the womb, placental DNA circulates in your blood and a blood-based test can analyse it. Once the tissue has passed or been removed, this DNA falls away: in one large Danish study, levels had dropped significantly after about 12 hours, and the share of tests giving no result rose from about 1 in 11 while tissue was in the womb to more than 1 in 4 at 12 to 24 hours after it passed.
A blood result is also less certain than a tissue result. Across eight studies, it found nearly 4 in every 5 of the chromosome changes that tissue testing found, so it is treated as a screening result rather than a diagnosis.
Tissue testing needs a fresh sample sent without formalin preservative. Both routes depend on planning before treatment; see testing before a miscarriage completes.
Does my age explain the miscarriage?
Not on its own. As eggs age, chromosome errors become more common, so the chance of miscarriage rises with age, more steeply from the late 30s. But miscarriage happens at every age, and only testing the pregnancy can show whether a chromosome difference was present in your case. Our miscarriage statistics guide sets out the age figures.
Could a test result change what happens in my next pregnancy?
It can. When a miscarriage was caused by a chance chromosome difference, the outlook for the next pregnancy is generally better than when the chromosomes were normal, although age still matters. A result that points to a rearrangement in a parent leads to genetics advice about the options. A normal result after several losses is a reason to look at other causes.
See preparing for your next pregnancy and pregnancy after a chromosomal miscarriage.
Do I need to live in London to see your genetic counsellors?
No. Genetic counselling takes place online by video, so you do not need to travel to London: a 30-minute appointment costs £80 and a 60-minute appointment costs £140. Scans take place in person at our London clinics.
Support
Support for you, whatever the results
Grief after miscarriage is real, whether or not a cause is found, and it can affect partners too. Miscarriage UK (the Miscarriage Association's working name) runs a support line on 0303 003 6464.
If you would like your loss formally recognised, our baby loss certificate guide explains how to apply in England, and our miscarriage care page lists other organisations that offer support.
About this information
This page gives general information about miscarriage and genetic testing. It is not a substitute for advice from a clinician who knows your history. If you have heavy bleeding, severe pain or a fever, or you feel faint, get help straight away from your early pregnancy unit or NHS 111. In an emergency, call 999.
Contact
Questions about testing after a miscarriage?
Sources & clinical references
The figures and clinical statements on this page are drawn from the sources below. Guidance evolves — always discuss your individual circumstances with a clinician.
- The Lancet (Quenby et al.)Miscarriage matters: the epidemiological, physical, psychological, and economic costs of early pregnancy loss2021
- RCOGPatient information: Recurrent miscarriage2023
- RCOGPatient information: Early miscarriage2016
- BMJ (Nybo Andersen et al.)Maternal age and fetal loss: population based register linkage study2000
- RCOGRecurrent Miscarriage (Green-top Guideline No. 17)2023
- ESHRERecurrent pregnancy loss guideline, update 20222023
- NICE Clinical Knowledge SummariesMiscarriage: risk factors2023
- NHS EnglandNational Genomic Test Directory: testing criteria for rare and inherited disease (v9.1)2026
- NICEEctopic pregnancy and miscarriage (NG126): management of miscarriage2026
- Human Reproduction (El Sammaa-Aru et al.)How big is the time window for cell-free fetal DNA testing after pregnancy loss and which factors are associated with a successful result?2026
- Prenatal Diagnosis (Pauta et al.)Genome-Wide Cell-Free DNA Analysis for Aneuploidy Detection in Miscarriages: Test Performance Meta-Analysis2025
- North West Genomic Laboratory Hub (Manchester University NHS FT)Acceptance criteria, requirements for cytogenetic analysis, and tissue disposal policy for solid tissue samples following loss or termination of pregnancy (Revision 15)2025