Recurrent miscarriage, usually defined as two or more pregnancy losses, affects roughly 1 in 50 couples trying to conceive. The frustrating reality is that in about half of cases, no single cause is ever identified. But that doesn’t mean nothing can be done. A growing number of treatable and identifiable factors are now part of the standard workup, and even among women with three or more unexplained losses, about 70% go on to have a live birth.
Chromosomal Problems in the Embryo
The most common reason any individual pregnancy ends in miscarriage is a random chromosomal error in the embryo. The fertilized egg ends up with too many or too few chromosomes, making normal development impossible. These errors become more frequent with age, which is why miscarriage rates climb sharply after 35 and especially after 40. Most of the time, this is pure chance and doesn’t repeat.
In a smaller number of couples, about 2% to 5% of those with recurrent losses, one partner carries a structural rearrangement in their own chromosomes called a balanced translocation. Their health isn’t affected, but when their chromosomes are passed to an embryo, the reshuffling can produce unbalanced combinations that end the pregnancy. A simple blood test called a karyotype, done on both partners, can detect this. If a translocation is found, IVF with preimplantation genetic testing can screen embryos before transfer.
Uterine Shape and Structure
The shape of your uterus plays a surprisingly large role in whether a pregnancy can be sustained. A septate uterus, where a wall of tissue partially divides the uterine cavity, is the most common structural issue linked to recurrent loss. Women with a septate or bicornuate (heart-shaped) uterus have second-trimester miscarriage rates around 13%, compared to just 1% in women with a normally shaped uterus. The septum has poor blood supply, so an embryo that implants on it may not get the nourishment it needs.
Fibroids that press into the uterine cavity and polyps can also interfere with implantation and early pregnancy. These structural issues are typically found through a saline-infusion ultrasound or a hysteroscopy, where a thin camera is inserted through the cervix. A uterine septum can often be surgically removed in a straightforward outpatient procedure, which significantly improves outcomes in subsequent pregnancies.
Antiphospholipid Syndrome
Antiphospholipid syndrome (APS) is one of the most important treatable causes of recurrent miscarriage. It’s an autoimmune condition where your immune system produces antibodies that make blood more likely to clot. During pregnancy, these tiny clots can form in the placenta, cutting off the blood supply to the developing baby.
APS is diagnosed when specific antibodies are found in your blood on two separate occasions at least 12 weeks apart. The key antibodies tested are lupus anticoagulant, anticardiolipin antibodies, and anti-beta-2 glycoprotein I antibodies. A pattern of three or more very early losses (before 10 weeks) or even a single loss after 10 weeks can point toward APS. Once diagnosed, treatment with low-dose aspirin and a blood-thinning injection during pregnancy dramatically improves live birth rates.
Hormonal and Thyroid Factors
Uncontrolled diabetes and thyroid disorders are well-established risk factors for pregnancy loss. Thyroid function is part of any standard recurrent miscarriage workup because both an overactive and underactive thyroid can disrupt pregnancy. What’s less clear is the role of thyroid antibodies in women whose thyroid hormone levels are actually normal. Research shows that women who test positive for thyroid peroxidase antibodies are about seven times more likely to develop subclinical hypothyroidism, so monitoring thyroid function early in pregnancy makes sense even if levels are fine beforehand.
Progesterone, the hormone that sustains early pregnancy, has long been debated as a treatment. The largest trial on the subject found that vaginal progesterone given to women with early pregnancy bleeding and a history of miscarriage improved live birth rates by about 5 percentage points overall. For women with three or more previous losses who were also bleeding in early pregnancy, the benefit jumped to 15 percentage points: 72% had a live birth with progesterone compared to 57% with placebo. This is one of the few interventions with strong evidence for a specific subgroup.
Chronic Infection of the Uterine Lining
Chronic endometritis is a low-grade, persistent inflammation of the uterine lining caused by bacteria. It usually produces no obvious symptoms, which is why it’s easy to miss. Studies of women with recurrent loss have found chronic endometritis in about 16% of cases. The condition is diagnosed through a biopsy of the uterine lining, where a pathologist looks for specific immune cells that shouldn’t be there in large numbers. When identified, a course of antibiotics can clear the infection, though research is still working out the best treatment protocols and how much this improves pregnancy outcomes.
Sperm DNA Damage
Recurrent miscarriage investigations have traditionally focused almost entirely on the woman, but the male partner’s contribution is becoming harder to ignore. Sperm DNA fragmentation, where the genetic material inside sperm is broken or damaged, has been consistently linked to recurrent pregnancy loss in multiple studies. Men whose partners experience repeated miscarriages tend to have higher levels of sperm DNA damage even when their standard semen analysis (count, motility, shape) looks completely normal.
The likely explanation is that a damaged sperm can still fertilize an egg and produce a positive pregnancy test, but the genetic errors it carries may be too severe for normal embryonic development, leading to loss after implantation. Greater sperm DNA damage has also been correlated with a higher number of losses. Sperm DNA fragmentation testing isn’t yet part of every standard workup, but it’s increasingly offered by fertility clinics, particularly when no maternal cause has been found. Lifestyle changes like quitting smoking, reducing alcohol, treating infections, and avoiding excessive heat exposure can improve sperm DNA quality.
What Testing Looks Like
Most specialists will begin a full evaluation after two consecutive losses, though some start after three. The workup typically includes blood tests for both partners’ chromosomes (karyotype), screening for antiphospholipid antibodies, thyroid function and thyroid antibodies, and sometimes tests for blood clotting disorders. An imaging study of the uterus, either a saline-infusion ultrasound or hysteroscopy, checks for structural problems like a septum, fibroids, or polyps. Some clinics will also test for chronic endometritis and sperm DNA fragmentation, especially when initial results come back normal.
If a pregnancy is lost during the evaluation process, genetic testing of the miscarriage tissue itself can be extremely informative. Finding a chromosomal abnormality in the tissue suggests that particular loss was likely random rather than caused by an ongoing problem in either parent.
The Odds Are Better Than You Think
One of the most important things to know is that the prognosis for recurrent miscarriage is genuinely good, even without a clear diagnosis. In a large study tracking women with unexplained recurrent loss, about 70% eventually had a live birth. Within the first year of follow-up, 40% had delivered a baby. By two years, that number rose to 61%. Women with exactly two prior losses had somewhat better odds than those with three or more, but the majority in both groups succeeded.
Age remains the strongest predictor of future success. The decline in egg quality after 35 increases both the per-pregnancy miscarriage risk and the time it may take to achieve a healthy pregnancy. For younger women with unexplained recurrent loss, time and supportive early pregnancy monitoring are often the most effective approach. For those with an identified cause, targeted treatment can shift the odds even further in your favor.