Recurrent Miscarriage: Causes, Risk Factors, and What You Can Do

In short: Recurrent miscarriage is defined in recent European guidance as two or more pregnancy losses, not necessarily in a row, while other guidance uses three or more. Causes include genetic errors, abnormalities of the uterus, and hormonal, immune and clotting disorders; in many couples no cause is found. Treatment depends on the cause, and supportive care alone gives good results in unexplained cases.

Recurrent miscarriage can be an emotionally difficult experience, and many patients want to understand why it happens. Below we explain the main known causes of recurrent miscarriage (abortion), based on current medical understanding.

1- Parental chromosome abnormalities causing Recurrent Miscarriage (Abortion):

Identified in between 3-5% of couples with recurrent miscarriage. The most common cause is a balanced or reciprocal translocation. Twice as many females compared with males are identified as carrying a structural chromosome abnormality; this is most likely because structural abnormalities in males are more often associated with infertility.

2- Fetal aneuploidy: -

Trisomy or monosomy is the most common chromosome abnormality identified in human miscarriage; about 30% of miscarriages involve trisomy, and this risk increases with maternal age.

3- Endocrinopathy causing Recurrent Miscarriage (Abortion): -

Luteal phase defect is seen in some women with recurrent miscarriage. Testing for ‘luteal phase defect’ with progesterone levels or endometrial biopsy is no longer recommended, because the results are unreliable. However, women who have had a previous miscarriage and have bleeding in early pregnancy benefit from vaginal progesterone (400 mg twice daily) until 16 weeks. Patients with PCOS are associated with a higher rate of pregnancy loss, as hormonal changes affect how receptive the endometrium is to the embryo.

4- Antiphospholipid syndrome: -

This is one of the most important treatable causes of recurrent miscarriage. Most miscarriages linked to this condition occur in the first trimester of pregnancy, after the fetal heartbeat is seen, and are thought to result from thrombosis (clotting) of the uteroplacental blood vessels. The recommended treatment is low-dose aspirin together with heparin injections, started early in pregnancy; with this combination about 70% or more of pregnancies end in a live birth, compared with about 40% with aspirin alone. As always, treatment should be personalized and discussed with your doctor.

5- Thrombophilic defects

6- Immune dysfunction which causes Recurrent Miscarriage (Abortion):-

• (NK) Natural killer cells: Lymphocytes that are part of the immune system, present in peripheral blood, and which have more killing ability than uterine natural killer (NK) cells.
• The embryo must be receptive to implantation. This requires continuous interaction between the embryo and the uterus, mainly through cytokines secreted by the immune cells of the uterus. If the immune cells do not respond properly to the signals from the embryo, adhesion and implantation may not occur.

Tests of natural killer (NK) cells or cytokines are not recommended routinely, and immune treatments (such as steroids, intralipid or immunoglobulin infusions) have not been shown to improve live birth rates, so international guidelines (ESHRE 2022) advise using them only in research settings.

7- Structural uterine abnormalities causing Recurrent Miscarriage (Abortion): -

The prevalence of uterine abnormalities among women with recurrent miscarriage ranges from 1.8% to 37.6%.

8- Uterine environment that inhibits embryo implantation, classified as anatomic, hormonal, and immunological:

• Endometrial polyps: Benign outgrowths of the endometrium in the uterine cavity.
• Sub mucous fibroids: Benign tumors which protrude from the uterine wall into the uterine cavity.
• Uterine synechiae: Scarring or adhesions in the uterine cavity.

9- Infectious agents causing Recurrent Miscarriage (Abortion)

10- Environmental factors: - tobacco, alcohol, radiation, chemotherapy

11- Psychological causes of Recurrent Miscarriage (Abortion).

12- Idiopathic (unknown cause): - accounts for about 40% of recurrent pregnancy loss cases

Frequently asked questions:

Why does early miscarriage occur?

In most cases, no specific cause can be identified, but the most common suspected cause is a chromosomal abnormality in the fetus.

Is two miscarriages considered recurrent miscarriage?

According to the European (ESHRE 2022) and American guidelines, two or more pregnancy losses are considered recurrent pregnancy loss, and a medical evaluation is reasonable after two miscarriages.

What does recurrent miscarriage indicate?

It may indicate an underlying issue with the mother — such as blood clotting disorders, a uterine problem, or a genetic issue causing chromosomal abnormalities in the fetus. A proper evaluation with your doctor can help identify the cause in your specific case.

How can I maintain a pregnancy after recurrent miscarriages?

Continuous follow-up with your doctor before trying to conceive again is essential to help determine the underlying cause and reduce the chance of it happening again.

Does recurrent miscarriage affect the uterus?

It can, especially if it was followed by a dilation and curettage (D&C) procedure.

What are the risks of recurrent miscarriage for the mother?

• Weak or damaged uterus, which may delay future pregnancy.

• Reproductive tract infections and pelvic inflammatory disease.

• Psychological effects that may persist for up to 6 months, such as anxiety and depression.

In which month is the risk of miscarriage lowest?

By around the 12th week of pregnancy, the risk of miscarriage generally decreases to around 5%.

Can artificial insemination help treat miscarriage?

Insemination itself does not prevent miscarriage. If one partner carries a chromosome translocation, IVF with genetic testing of the embryos (PGT) may be an option, although many such couples also have a healthy baby naturally. Testing embryos for chromosome number (PGT-A) is not recommended for unexplained recurrent miscarriage. This should be discussed individually with your fertility specialist.

Can the husband be a cause of recurrent miscarriage?

Yes, this is possible if there is a chromosomal abnormality on the father’s side.

Is it a hereditary disease?

Usually not. However, if one parent carries a balanced chromosome translocation, it can be passed on and can cause recurrent miscarriage; this is why chromosome testing of the couple may be offered.

What factors increase the chances of miscarriage?

Age over 30

Uncontrolled health conditions such as diabetes

Maternal obesity

When is a dilation and curettage (D&C) procedure necessary?

• Heavy, persistent bleeding
• Signs of infection
• If medications are ineffective

Is intercourse safe during pregnancy?

Yes. Intercourse does not cause miscarriage and is safe in pregnancy, unless you have bleeding or your doctor has advised against it for a specific reason. Your doctor can give guidance tailored to your situation.

If you have experienced recurrent miscarriage, know that you are not alone, and that a thorough evaluation can help guide the next steps in your journey toward a healthy pregnancy.

The embryo testing carried out with the laboratory is described in our article on preimplantation genetic diagnosis (PGD).

Dr. Najeeb Layyous and his team are available to discuss your individual case and possible options.

Dr Najeeb Layyous F.R.C.O.G

Consultant Obstetrician, Gynecologist and Infertility Specialist