Repeated pregnancy loss has an identifiable cause in roughly half of cases, and even when no cause is found, the odds of eventually carrying to term are strongly in your favor. In a study of 228 couples who had experienced three or more first-trimester miscarriages, 76% delivered a baby within two years. That number won’t erase the grief of losses you’ve already been through, but it’s worth knowing early: this is not a hopeless situation, and there are concrete things worth investigating.
In the U.S., the clinical term “recurrent pregnancy loss” applies after two or more consecutive failed pregnancies confirmed by ultrasound or tissue examination. In the U.K., the threshold is three. Either way, reaching that point warrants a thorough workup to look for treatable causes.
Chromosomal Problems in the Embryo
The single most common reason any pregnancy fails is a random genetic error in the embryo itself. Across a large study of over 7,000 miscarriages, chromosomal abnormalities were found in 67% of lost pregnancies. These aren’t inherited conditions. They’re errors that happen during cell division at or shortly after fertilization, and they make it impossible for the embryo to develop normally.
Age plays a significant role. In women around age 23, about 55% of miscarriages show chromosomal abnormalities. That proportion stays above 60% through the mid-thirties, then jumps sharply: at 37, it’s around 64%, but by 38 it surges to 79%. By age 44, roughly 94% of miscarriages are chromosomally abnormal. This steep climb after 37 is one reason repeated loss becomes more common with age, and it’s also why the prognosis for future pregnancies can be better than it feels. A chromosomally abnormal loss doesn’t mean something is wrong with you. It means that particular embryo was never viable.
If you’ve had multiple losses, your doctor may suggest genetic testing of the pregnancy tissue (if available) to determine whether chromosomal errors were the cause. Parental chromosome testing is not routinely recommended because the chance of finding a structural rearrangement in either partner is low, but it may be considered on a case-by-case basis.
Uterine Shape and Structural Issues
The physical structure of your uterus matters more than most people realize. Some women are born with a uterine shape that makes it harder for a pregnancy to grow, such as a uterus divided by a wall of tissue (a septum), a uterus with an unusual shape, or one that developed incompletely. These variations can restrict blood flow to the area where the embryo implants or limit the space available as it grows.
Acquired structural problems can also play a role. Scar tissue inside the uterus from prior procedures, noncancerous growths (fibroids) that push into the uterine cavity, and polyps on the uterine lining have all been linked to recurrent loss. These conditions distort the cavity in ways that interfere with implantation or disrupt the blood supply the embryo needs. The encouraging part is that many of these are surgically correctable, and an assessment of your uterine anatomy is one of the standard recommendations after recurrent loss.
Thyroid Function
Your thyroid sets the metabolic pace for your entire body, and during pregnancy, even mild dysfunction can raise the risk of miscarriage. The key marker is TSH, the hormone your brain produces to signal your thyroid. During the first trimester, the recommended range is 0.1 to 2.5 mIU/L. Women whose levels fall between 2.5 and 4.87 have about a 47% higher risk of miscarriage compared to those in the normal range. Above 4.87, the risk nearly doubles.
What makes thyroid problems particularly worth investigating is that they’re straightforward to treat. A simple blood test identifies the issue, and medication can bring levels into a safe range before or early in pregnancy. Thyroid screening is one of the standard tests recommended after recurrent loss.
Antiphospholipid Syndrome
Antiphospholipid syndrome (APS) is an autoimmune condition where the body produces antibodies that promote blood clotting. During pregnancy, these antibodies can interfere with the placenta’s development, restrict blood flow to the embryo, and trigger early miscarriage. APS can also cause complications later in pregnancy, including severe preeclampsia and poor fetal growth.
Diagnosis requires both a clinical event (such as recurrent miscarriage) and the presence of specific antibodies in the blood, confirmed on two separate tests at least 12 weeks apart. The repeat testing matters because these antibodies can appear temporarily during infections or other illnesses. The most predictive marker is called lupus anticoagulant, despite having nothing to do with lupus in most cases.
APS is one of the most treatable causes of recurrent pregnancy loss. Treatment typically involves blood-thinning medication during pregnancy, and it substantially improves outcomes for women who have the condition.
Chronic Endometritis
Chronic endometritis is a low-grade, persistent inflammation of the uterine lining. It’s not the dramatic infection you might picture. About 25% of women who have it experience no symptoms at all, and even when symptoms are present, they tend to be vague enough to go unnoticed for long stretches.
This quiet inflammation appears to disrupt the immune environment that a developing embryo depends on for implantation and early growth. A meta-analysis found chronic endometritis in nearly 38% of women with recurrent pregnancy loss, compared to about 16% in women without that history. That’s more than a threefold increase in odds. Diagnosis requires a biopsy of the uterine lining, and treatment with antibiotics can resolve the inflammation, potentially restoring normal conditions for pregnancy.
The Male Factor
Pregnancy loss is often treated exclusively as a female health issue, but the male partner contributes half the embryo’s DNA. Damage to sperm DNA, known as DNA fragmentation, has been associated with higher miscarriage rates. A meta-analysis of 16 studies covering nearly 3,000 patients found that high sperm DNA damage more than doubled the risk of miscarriage compared to low damage.
That said, the research picture is complicated. Prospective studies have not consistently confirmed that sperm DNA fragmentation testing can reliably predict which couples will experience recurrent loss, and it’s not yet part of the standard workup. Still, factors that damage sperm DNA, including smoking, excessive heat exposure, obesity, and advanced paternal age, are modifiable. Addressing them is reasonable even without a formal test result.
When No Cause Is Found
After a full evaluation, roughly half of couples with recurrent pregnancy loss receive no definitive diagnosis. This is called “unexplained” recurrent loss, and while the label is frustrating, the outcomes are actually better than many people expect. The 76% live birth rate within two years mentioned earlier came from a study of couples with three or more unexplained first-trimester losses. For women with fewer prior losses or who are younger, the odds are generally even better.
One treatment that comes up frequently in this situation is progesterone supplementation in early pregnancy. A large randomized trial assigned over 800 women with a history of unexplained recurrent miscarriage to receive either progesterone or a placebo through the first 12 weeks. The live birth rate was 65.8% with progesterone and 63.3% with placebo, a difference too small to be meaningful. Progesterone did not cause harm, but it did not improve outcomes for this group.
What Testing Looks Like
The standard workup after recurrent loss focuses on the causes most likely to be identified and treated. You can expect blood tests to check thyroid function and screen for antiphospholipid antibodies. Imaging of your uterus, often using a saline-infused ultrasound, can reveal structural abnormalities, polyps, fibroids, or adhesions. If chronic endometritis is suspected, a biopsy of the uterine lining may be recommended.
Screening for inherited blood-clotting disorders (thrombophilia) is sometimes discussed but is not routinely recommended. The association between hereditary thrombophilia and recurrent loss is weak, and there is no well-supported treatment for it in this context. Similarly, routine chromosome testing of both partners is not standard, though it may be appropriate in specific circumstances based on family history or the pattern of losses.
The goal of testing is not to find every possible abnormality but to identify the causes that have effective treatments. For many couples, even a single treatable finding can change the trajectory of future pregnancies.