Why Do I Keep Miscarrying What Doctors Look For?

Miscarriage is the most common complication of early pregnancy. It happens in roughly 1 in 5 known pregnancies, and the true number is likely higher because many losses occur before a person even knows they are pregnant. If you have had more than one, you are almost certainly asking why — and that question deserves a real answer, not a vague reassurance.

Doctors look for a pattern. A single miscarriage is usually treated as bad luck, because most early losses are caused by random chromosomal errors that are unlikely to repeat. Two or more losses shift the search toward identifiable causes: chromosome problems in the parents, uterine shape, blood-clotting disorders, thyroid and other hormone conditions, and, less often, immune factors. The specific tests depend on your history, your age, and whether the losses were early or late.

Here is what that evaluation actually involves, and what the evidence does and does not support.

How common is miscarriage, really?

Miscarriage is defined as pregnancy loss before 20 weeks. The great majority happen in the first trimester.

The risk is highest very early. Some research indicates that a large share of fertilized eggs never implant or are lost within days of implantation, often without a missed period. Among pregnancies that are confirmed by a positive test, the chance of loss falls steadily as the pregnancy progresses. Age is the strongest single factor. The risk rises noticeably after age 35 and more steeply after 40, largely because egg quality declines with age and chromosomal errors become more common.

This matters for how you read your own history. One loss is common. Recurrent miscarriage — generally defined as two or more consecutive losses, or three or more total losses — is far less common and is the point at which a structured evaluation becomes worthwhile.

Why do most early miscarriages happen?

Most first-trimester miscarriages are caused by chromosomal abnormalities in the developing embryo. These are almost always random events, not something inherited from either parent.

When an egg and sperm combine, the resulting cell needs exactly the right number of chromosomes. Sometimes it ends up with too many or too few. The pregnancy may start, produce a positive test, and then stop developing because the genetic instructions cannot support life past a certain point. This is not caused by exercise, stress, sex, lifting, or a fall. It is not caused by a single cup of coffee or one glass of wine.

That is why a single miscarriage is usually not investigated. If the cause was a random chromosomal error, the chance it repeats is low. The picture changes when losses stack up, because random events become a less convincing explanation.

Why do I keep miscarrying what doctors look for first?

When there is a pattern, doctors work through a short list of causes that are known to repeat. The order depends on your history, but the usual starting points are these.

Chromosome problems in the parents. A blood test can check whether either partner carries a balanced translocation — a rearrangement of chromosomes that causes no symptoms in the carrier but can lead to unbalanced, non-viable pregnancies. This is an uncommon cause of recurrent loss, but it is testable and it changes counseling, so it is often checked early.

Testing the pregnancy tissue itself. If tissue from a loss is available, testing it can show whether that particular miscarriage was chromosomal. A normal result points away from random error and toward another cause. This is one of the most useful pieces of information in the whole workup, and it is often not offered unless you ask.

Uterine structure. A uterus divided by a band of tissue (a septum), scar tissue, fibroids that distort the cavity, or polyps can interfere with implantation or blood supply. These are found with imaging — typically a saline infusion sonogram or hysteroscopy. Some, like a septum, can be surgically corrected, though whether correction improves live birth rates is debated and the evidence is mixed.

Antiphospholipid syndrome. This is a blood-clotting disorder and one of the few causes of recurrent miscarriage with a clear, established treatment. It is diagnosed through specific blood antibody tests, and confirmation requires repeat testing because a single positive result can be transient.

Thyroid and metabolic conditions. Poorly controlled thyroid disease and uncontrolled diabetes are associated with higher miscarriage risk. These are checked with blood tests and are treatable.

Several other factors are investigated less consistently, including hormonal conditions such as polycystic ovary syndrome, and certain immune and clotting factors. Evidence for some of these is weaker, and practice varies between clinics.

What does the evaluation actually involve?

A recurrent miscarriage workup is mostly blood tests and imaging. It is not usually invasive, and it can often be done between pregnancies.

• Blood tests for parental chromosomes (karyotype)
• Antibody tests for antiphospholipid syndrome, repeated after a set interval to confirm any positive result
• Thyroid function and blood sugar testing
• Imaging of the uterus — saline sonogram or hysteroscopy
• Testing of pregnancy tissue from a prior loss, when available

One thing worth knowing: in a substantial share of couples, this full evaluation finds no clear cause. That is called unexplained recurrent miscarriage. It is frustrating, and it is common. It does not mean nothing can be done, but it does mean the evidence for the remaining options is weaker.

What treatments have real evidence behind them?

This is where honesty matters most, because recurrent miscarriage is a field where unproven treatments are widely offered.

For antiphospholipid syndrome, treatment with low-dose aspirin plus a blood thinner (heparin) is well established and improves outcomes. This is the clearest example of a cause-and-treatment match in the entire field.

For thyroid disease, correcting thyroid levels before and during pregnancy is standard and supported.

For a uterine septum, surgical removal is commonly performed, but the evidence that it improves live birth rates is genuinely mixed. Some clinicians recommend it; others are more cautious. It is reasonable to ask your doctor what the data show for your specific situation.

For unexplained recurrent miscarriage, several treatments are used in practice without strong trial support. Progesterone supplementation is being studied and some guidelines now suggest it may help in certain cases of early pregnancy bleeding, but it is not a proven fix for recurrent loss across the board. Immunologic treatments, including intralipid infusions and intravenous immunoglobulin, are offered by some clinics. No large, well-controlled human trials have confirmed that these improve live birth rates, and they carry cost and risk. If a clinic offers them as established fact, that is a reason for caution.

The honest position: for many people with recurrent loss, the most evidence-based path is careful monitoring, treatment of any specific cause that is found, and time. That is not a satisfying answer, but it is the accurate one.

Does age change the picture?

Yes, and it is the factor most outside anyone’s control. Advancing maternal age raises the chance that any given pregnancy will have a chromosomal error, which raises the chance of loss. This is biology, not blame.

Because age affects the odds independently of any other cause, a doctor will weigh it when interpreting your history. Two losses at 42 and two losses at 28 are not the same clinical situation, even though the number is identical. Age also affects how quickly a doctor may move to testing, since time matters if you want to try again.

What can I actually do?

Ask for the evaluation rather than waiting for a third or fourth loss. If you have had two or more consecutive losses, you are entitled to ask what testing is appropriate for you.

Ask specifically whether tissue from a prior loss can be tested, if it was not already. That single result can redirect the entire workup.

Ask which of your findings have a treatment with proven benefit, and which do not. A good clinician will tell you the difference. If a treatment is described as a sure thing, ask what trial supports that.

Take care of the things that are genuinely within reach: manage thyroid disease and diabetes, avoid smoking and heavy alcohol use, and work with a doctor on any chronic condition before trying again. These steps are supported. They are not guarantees.

And know that recurrent miscarriage, even when no cause is found, does not mean you will never carry a pregnancy. Many people with unexplained recurrent loss go on to have a successful pregnancy. That is not a promise, but it is a real and common outcome.