pregnancy & babyGuide

Recurrent Pregnancy Loss: What Can Cause It?

Today, recurrent pregnancy loss (RPL) is generally defined as two or more spontaneous pregnancy losses, although detailed definitions and evaluation criteria can vary between professional organizations and healthcare systems. The losses do not necessarily have to be consecutive.

A single miscarriage is relatively common. When pregnancy loss happens repeatedly, your healthcare provider may recommend looking for factors that could be contributing. Even after a thorough evaluation, however, no clear cause is found in many cases.

One of the strongest factors affecting miscarriage risk is maternal age. As age increases, chromosomal abnormalities in the egg become more common, which increases the chance of miscarriage. Other factors that may be considered include uterine abnormalities, certain endocrine conditions, antiphospholipid syndrome, genetic or chromosomal factors, and lifestyle factors.

1) Uterine abnormalities

The shape of the uterus or abnormalities within the uterine cavity can sometimes affect the ability to maintain a pregnancy. Congenital conditions include a septate uterus, bicornuate uterus, and uterine didelphys.

Acquired conditions such as submucosal fibroids, endometrial polyps, and intrauterine adhesions may also distort the uterine cavity and affect pregnancy.

How are they evaluated?

Tests may include transvaginal ultrasound, 3D ultrasound, or saline infusion sonohysterography. In some situations, hysterosalpingography (HSG), hysteroscopy, or MRI may also be used. The most appropriate test depends on the suspected condition.

How are they treated?

Hysteroscopic surgery may be considered for selected cases of a uterine septum, cavity-distorting submucosal fibroids, polyps, or adhesions. Not every uterine abnormality requires surgery, and the evidence that surgery reduces recurrent miscarriage varies depending on the condition. Treatment should therefore be individualized.

2) Endocrine conditions

Poorly controlled diabetes and thyroid disease can affect pregnancy outcomes and may be evaluated in people with recurrent pregnancy loss.

If you have diabetes, good blood glucose control before conception and during pregnancy is important. Poorly controlled diabetes can increase the risks of miscarriage, congenital abnormalities, and other pregnancy complications.

Thyroid conditions should also be appropriately treated. Levothyroxine can be used to treat hypothyroidism, with the dose adjusted according to thyroid blood tests and pregnancy needs.

3) Antiphospholipid syndrome (APS)

Antiphospholipid syndrome (APS) is an autoimmune condition associated with abnormal blood clotting and certain pregnancy complications. It is one of the established causes associated with recurrent pregnancy loss.

APS is not diagnosed from a single positive antibody test. Diagnosis is based on specific clinical features together with persistent antiphospholipid antibodies on appropriate blood testing.

For confirmed obstetric APS, treatment during pregnancy may include low-dose aspirin together with heparin or low-molecular-weight heparin (LMWH), depending on your individual situation.

By contrast, routine testing for inherited thrombophilias in everyone with recurrent pregnancy loss is not currently recommended, and aspirin or heparin should not routinely be prescribed solely for unexplained RPL or inherited thrombophilia.

4) Chromosomal and genetic factors

One of the most common causes of miscarriage is a random chromosomal number abnormality (aneuploidy) in the embryo or fetus. Most are not directly inherited from the parents but occur by chance during the formation of the egg or sperm or during early embryonic cell division. The likelihood increases with maternal age.

In recurrent pregnancy loss, chromosome testing of pregnancy tissue may sometimes help explain why a particular pregnancy ended. If a structural chromosome rearrangement such as a balanced translocation is suspected, or an abnormality is found in pregnancy tissue, parental chromosome testing and genetic counseling may be considered.

For patients undergoing IVF, different forms of preimplantation genetic testing (PGT) may be available: PGT-M for monogenic conditions, PGT-SR for structural chromosome rearrangements, and PGT-A for aneuploidy.

However, PGT-A has not been shown to guarantee a lower miscarriage rate or a higher live-birth rate for unexplained recurrent pregnancy loss. Whether it is appropriate depends on factors such as age, previous chromosome results, and ovarian function.

5) Lifestyle factors

Smoking is associated with an increased risk of miscarriage and several other pregnancy complications, so quitting smoking is recommended when planning pregnancy.

Alcohol should be avoided during pregnancy, and excessive caffeine intake should be limited. Maintaining a healthy weight, eating a balanced diet, and staying appropriately active can also support overall pregnancy health.

However, recurrent pregnancy loss should not be attributed to one lifestyle choice alone. Pregnancy loss is usually multifactorial, and it should not be assumed that it occurred because of something the pregnant person did.

Sometimes no cause is found

Even after a complete evaluation, no clear cause is found in many people with recurrent pregnancy loss. An unexplained result does not mean that another miscarriage is inevitable, and many people subsequently have a healthy pregnancy and live birth.

If you have experienced two or more pregnancy losses, consider talking with an obstetrician or reproductive medicine specialist about which tests are appropriate based on your pregnancy history, age, and overall health.