Most miscarriages at 11 weeks are caused by chromosomal abnormalities in the embryo, accounting for roughly 50 to 60 percent of all first-trimester losses. These are random genetic errors that prevent the pregnancy from developing normally, and they are not caused by anything the parent did or didn’t do. Other causes include maternal health conditions, uterine structural problems, infections, and placental development failures.
Chromosomal Abnormalities Are the Leading Cause
When cells divide in the earliest stages of embryo development, chromosomes sometimes end up with extra copies or missing pieces. The most common type is trisomy, where the embryo has three copies of a chromosome instead of two. In one study of 162 miscarriages, chromosomal abnormalities were found in over 62 percent of cases, and among those, single autosomal trisomy accounted for more than 76 percent of the abnormal results.
These errors are largely random. They become more common with age, particularly after 35, but they happen at every age. An embryo with a major chromosomal abnormality typically cannot develop functioning organs, and the pregnancy ends because the embryo was never viable. This is the body recognizing that normal development has stopped.
Even the placenta shows physical signs of these genetic problems. Pathology studies of unexplained miscarriages found that over 86 percent had abnormally shaped structures in the placental tissue, a marker strongly associated with genetic abnormalities including trisomies and other chromosomal conditions. In many cases, the same genetic errors that disrupt placental cell growth also affect the development of critical organs like the heart.
Maternal Health Conditions
Several chronic health conditions increase the risk of pregnancy loss at 11 weeks. Uncontrolled diabetes, thyroid disorders, and polycystic ovary syndrome (PCOS) all raise the likelihood of miscarriage. High blood pressure and autoimmune disorders, where the immune system mistakenly attacks the body’s own tissues, are also significant risk factors. The National Institute of Child Health and Human Development identifies managing these conditions before conception as one of the most effective ways to reduce risk.
Thyroid problems deserve special attention because they’re common and often go undiagnosed. Both an overactive and underactive thyroid can interfere with the hormonal environment the pregnancy depends on. Similarly, uncontrolled blood sugar in diabetes can disrupt early fetal development during exactly the period leading up to 11 weeks, when organs are forming.
Uterine Structural Problems
The shape and condition of the uterus matters. Fibroids, which are noncancerous growths in the uterine wall, have been reported to increase miscarriage risk by approximately 60 percent, with some estimates putting the risk as high as three times greater than normal. The location of the fibroid matters more than its size. Fibroids that grow into the uterine cavity (submucous fibroids) are more likely to interfere with implantation and blood supply to the developing pregnancy than those growing outward from the uterine wall.
A uterine septum, which is a wall of tissue dividing the uterine cavity, is another structural issue. It reduces the available space for the pregnancy to grow and can limit blood flow to the implantation site. Both conditions can be identified through ultrasound and, in many cases, treated before a future pregnancy.
Infections That Can Trigger Loss
Certain infections pose a particular threat during early pregnancy. Listeria, the bacteria found in unpasteurized dairy, deli meats, and some ready-to-eat foods, can cross the placenta and cause spontaneous abortion and preterm labor. Toxoplasmosis, spread through undercooked meat or contact with infected cat litter, can lead to stillbirth and severe neurological damage. Cytomegalovirus (CMV), a common virus that many people carry without symptoms, can damage the fetal nervous system, kidneys, lungs, and liver if transmitted during pregnancy.
These infections are preventable with basic precautions: cooking meats thoroughly, avoiding unpasteurized products, washing produce, and having someone else handle cat litter during pregnancy.
Body Weight and Lifestyle Factors
Being significantly underweight or overweight increases miscarriage risk. A large meta-analysis found that both underweight women and those with a BMI over 25 had about 20 percent higher odds of recurrent pregnancy loss. For women who had already experienced repeated miscarriages, having a BMI over 30 raised the odds of another loss by 77 percent.
The evidence on caffeine and alcohol is less definitive than often reported. Current guidelines generally recommend limiting caffeine to around 200 milligrams per day (roughly one 12-ounce cup of coffee), though researchers have noted that larger, better-designed studies are still needed to fully clarify the relationship between caffeine, alcohol, and recurrent loss. What is clear is that heavy alcohol use and smoking both increase risk.
Subchorionic Hematoma
A subchorionic hematoma is a collection of blood between the placenta and the uterine wall. It’s a common finding on early ultrasounds and often causes vaginal bleeding that can be alarming. However, recent research in a large singleton pregnancy study found that the size of the hematoma was not directly linked to pregnancy loss before 20 weeks. Small hematomas were actually more likely to cause noticeable bleeding than larger ones, even though larger ones (those covering more than 25 percent of the gestational sac) did carry a fivefold increased risk of placental abruption later in pregnancy.
If you’ve been told you have a subchorionic hematoma, it doesn’t necessarily mean the pregnancy is in danger. Most resolve on their own without affecting the outcome.
How Risk Changes by 11 Weeks
By 11 weeks, the overall risk of miscarriage has already dropped significantly compared to earlier in the first trimester. Research on women with a history of recurrent miscarriage showed that seeing a heartbeat at 8 weeks gave a 98 percent chance of the pregnancy continuing, and by 10 weeks that rose to 99.4 percent. For women without a history of previous losses, the numbers are likely even more favorable.
This means that while miscarriage at 11 weeks does happen, it is uncommon once a heartbeat has been confirmed. When it does occur this late in the first trimester, it is more likely to be a “missed miscarriage,” where the embryo has stopped developing but the body hasn’t yet recognized the loss. This is typically discovered at a routine ultrasound rather than through sudden symptoms.
What Happens After a Loss at 11 Weeks
When a miscarriage is confirmed at 11 weeks by ultrasound, there are three options: waiting for the body to pass the tissue naturally, using medication to help the process along, or having a minor procedure called uterine aspiration.
Medication management typically involves taking one pill in a clinic followed by a second medication at home 24 to 72 hours later, which causes cramping and bleeding as the uterus empties. When both medications are used together, about 84 percent of women complete the process within four days without needing any procedure. Using only one of the two medications drops that success rate, with up to 30 percent of women needing an additional dose or a procedure afterward.
Uterine aspiration is a brief outpatient procedure that is highly effective and carries low complication rates. Medical and surgical approaches have similar overall effectiveness. The choice often comes down to personal preference: some people prefer the privacy of managing at home, while others want the certainty and speed of a procedure. Both are safe, and neither affects the ability to become pregnant again.