Recurrent miscarriage can be an upsetting and difficult experience. Although miscarriage is relatively common, repeated pregnancy loss is much less common and may need further investigation.
This article explains what recurrent miscarriage means, the factors that may increase the risk, the tests that may be offered and the treatments that may help.
What is recurrent miscarriage?
Recurrent miscarriage is traditionally defined as having three or more miscarriages during the first trimester of pregnancy.
It affects around 1 in 100 women.
Having recurrent miscarriages does not necessarily mean that you will be unable to have a successful pregnancy in the future. In many cases, no clear cause is found, and many women will still go on to have a healthy pregnancy.
What increases the risk of miscarriage?
Several factors can increase the chance of miscarriage.
These include:
- Increasing maternal age
- Increasing paternal age, although the effect is less marked than maternal age
- Smoking
- Excessive alcohol intake
- High caffeine intake
- Being underweight or overweight
- Having had previous miscarriages
- Black ethnic background
A healthy weight is generally considered to be a BMI between 19 and 25 kg/m² when trying to reduce potentially modifiable risk factors.
How does age affect miscarriage risk?
The chance of miscarriage rises considerably as a woman gets older, particularly after the age of 35.
Approximate miscarriage risks by age are:
| Age | Risk of miscarriage |
| 12–19 years | 13% |
| 20–24 years | 11% |
| 25–29 years | 12% |
| 30–34 years | 15% |
| 35–39 years | 25% |
| 40–44 years | 51% |
| 45 years or older | 93% |
One important reason for this increase is that chromosomal abnormalities in eggs become more common with age.
Does having one miscarriage increase the risk of another?
The risk does rise as the number of previous miscarriages increases.
Approximate risks are:
| Previous miscarriages | Risk of another miscarriage |
| 1 | 11.3% |
| 2 | 17.0% |
| 3 | 28.0% |
| 4 | 39.6% |
| 5 | 47.2% |
| 6 | 63.9% |
These figures describe overall risk and cannot predict exactly what will happen in an individual pregnancy.
What causes recurrent miscarriage?
There are several possible causes. Sometimes more than one factor may be involved, and in some women no clear
explanation is found.
1. Blood-clotting conditions
Certain conditions affecting the way the blood clots may be associated with miscarriage.
Antiphospholipid syndrome — APS. 15% of recurrent miscarriages occur as a result of APS, and it is now recognised as the most common, treatable cause.
Antiphospholipid syndrome is an acquired condition in which the immune system produces abnormal antibodies that can increase the tendency for blood to clot.
These antibodies include:
- Lupus anticoagulant
- Anticardiolipin antibodies
- Anti-beta-2-glycoprotein-I antibodies
APS can be associated with pregnancy complications including:
- Three or more consecutive miscarriages before 10 weeks
- One or more losses of a normally formed baby after 10 weeks
- One or more premature births before 34 weeks because of problems with the placenta
Among these antibodies, lupus anticoagulant has the strongest association with recurrent miscarriage.
2. Inherited blood-clotting conditions
Some people inherit conditions that make their blood more likely to clot. These are known as inherited thrombophilias.
Examples include:
- Factor V Leiden
- Prothrombin gene mutation
- Protein S deficiency
- Protein C deficiency
- Antithrombin deficiency
The relationship between these conditions and miscarriage is complicated.
The association appears to be stronger with second-trimester miscarriage than with early first-trimester miscarriage.
Factor V Leiden and the prothrombin gene mutation have both been associated with recurrent miscarriage, while the evidence for some other inherited thrombophilias is less consistent.
Importantly, finding an inherited thrombophilia does not automatically mean that treatment will prevent miscarriage.
3. Genetic and chromosome problems
Chromosome problems are one of the most common causes of miscarriage.
Around half of isolated or sporadic miscarriages are associated with a chromosomal abnormality in the pregnancy.
Approximately half of these chromosomal abnormalities are due to a condition called trisomy, where the pregnancy has an extra copy of a chromosome.
Sometimes one of the parents carries a rearrangement of their chromosomes without being affected themselves. This can occasionally result in an embryo receiving an unbalanced set of chromosomes.
4. Abnormalities in the shape of the womb
Some women are born with a differently shaped uterus.
Examples include:
- Septate uterus
- Bicornuate uterus
- Unicornuate uterus
A septate uterus occurs when a wall of tissue divides part or all of the inside of the womb.
Certain uterine abnormalities may increase the risk of miscarriage, particularly miscarriage occurring later in pregnancy.
5. Thyroid and hormonal factors
Thyroid problems may also be relevant in women experiencing recurrent miscarriage.
Tests may therefore include:
- Thyroid-stimulating hormone — TSH
- Thyroid peroxidase antibodies — TPO antibodies
The presence of thyroid antibodies does not necessarily mean that thyroid treatment is required.
What tests may be offered?
Women with recurrent first-trimester miscarriages or one or more second-trimester miscarriages may be offered several investigations.
Tests for antiphospholipid syndrome
Blood testing may include:
- Lupus anticoagulant
- Anticardiolipin antibodies
To confirm APS, the abnormal antibody test generally needs to be positive on two separate occasions at least 12 weeks apart.
Testing should also usually be performed at least six weeks after a miscarriage.
Testing for inherited thrombophilia
Women who have experienced a second-trimester miscarriage may sometimes be offered testing for:
- Factor V Leiden
- Prothrombin gene mutation
- Protein S deficiency
However, the evidence that treating these conditions improves the chance of a successful pregnancy remains limited.
Chromosome testing
Testing of the pregnancy tissue may be offered following:
- The third or subsequent miscarriage
- Any second-trimester miscarriage
If the pregnancy tissue shows a particular structural chromosome abnormality, both parents may be offered blood tests to examine their chromosomes.
If a chromosome abnormality is found in one of the parents, referral to a clinical geneticist or genetic counsellor may be recommended.
Ultrasound examination of the womb
Women with recurrent miscarriage may be offered an ultrasound scan to assess the shape of the uterus.
A 3D ultrasound scan is particularly useful for identifying congenital abnormalities such as a uterine septum.
Thyroid tests
Blood tests may include:
- TSH
- Thyroid peroxidase antibodies
These can help identify thyroid disease or thyroid autoimmunity that may require monitoring.
How is recurrent miscarriage treated?
Treatment depends on whether a particular cause has been identified.
Lifestyle changes
Women experiencing recurrent miscarriage are generally advised to:
- Aim for a BMI between 19 and 25 kg/m²
- Stop smoking
- Limit alcohol
- Keep caffeine intake below 200 mg per day
These changes cannot prevent every miscarriage, but they may help reduce avoidable risks and improve general pregnancy health.
Treatment for antiphospholipid syndrome
Women diagnosed with APS may be offered a combination of:
- Low-dose aspirin
- Heparin injections, usually low-molecular-weight heparin
For example, treatment may involve low-dose aspirin together with daily enoxaparin injections beginning after a positive pregnancy test.
The exact medication, dose and duration should be decided by the woman’s specialist team.
What about inherited thrombophilia?
There is currently insufficient evidence to routinely prescribe blood-thinning treatment simply to prevent miscarriage in women with conditions such as:
- Factor V Leiden
- Protein S deficiency
- Prothrombin gene mutation
However, treatment may still be recommended for some women because these conditions can also increase the risk of developing blood clots.
The decision therefore needs to be individualised.
Treatment when a chromosome problem is found
If one partner carries a chromosome rearrangement, several reproductive options may be discussed.
These may include:
- Trying naturally again
- IVF with preimplantation genetic testing for structural rearrangements — PGT-SR
- Using donated eggs or sperm
Not every couple needs assisted reproduction. Management should be personalised after discussion with a genetics and fertility specialist.
Treatment for uterine abnormalities
Women with recurrent miscarriage who have a uterine septum may be offered surgery to remove the septum.
This is usually performed using a small camera passed through the cervix into the womb, known as hysteroscopic surgery.
The potential benefits and uncertainties should be discussed with a specialist.
Thyroid treatment
Women who have normal thyroid function but positive thyroid antibodies do not routinely need thyroxine treatment simply because of a history of miscarriage.
Treatment may be considered when thyroid-stimulating hormone levels are more significantly raised, particularly when TSH is above 4 mIU/L.
Women with thyroid antibodies or subclinical hypothyroidism may need their thyroid function checked during early pregnancy, often beginning around 7–9 weeks.
Can progesterone help?
Progesterone may help a particular group of women.
Women who:
- Have previously experienced recurrent miscarriages, and
- Develop vaginal bleeding during a new early pregnancy
may be offered micronised vaginal progesterone.
A commonly used regimen is:
400 mg vaginal progesterone twice daily, continued until 16 weeks of pregnancy where appropriate.
Women experiencing bleeding in early pregnancy should contact their healthcare team for assessment rather than starting medication themselves.
What about endometrial scratching?
Endometrial scratching is not recommended as a treatment for recurrent miscarriage.
There is insufficient evidence that deliberately scratching the lining of the womb improves the chances of a successful pregnancy.
The most important message
Recurrent miscarriage can have several possible causes, including chromosome abnormalities, antiphospholipid syndrome, abnormalities of the uterus and some hormonal or medical conditions.
For many couples, however, extensive investigation does not identify a definite cause.
This does not mean that a successful pregnancy is impossible.
Specialist recurrent miscarriage services can provide investigations, treatment where appropriate, early pregnancy monitoring and emotional support during future pregnancies.
If you have experienced repeated miscarriages, speak to your GP, gynaecologist or early pregnancy team about whether referral to a recurrent miscarriage clinic is appropriate.
This article is intended for general education and does not replace individual medical advice from your healthcare professional.