A missed miscarriage happens when an embryo stops developing or never develops at all, but the body doesn’t recognize the loss and continues acting pregnant. Nearly two-thirds of missed miscarriages are caused by chromosomal abnormalities in the embryo, meaning the most common cause is a random genetic error that occurs at or shortly after conception. The remaining cases involve a mix of hormonal, immune, and maternal health factors.
What makes a missed miscarriage different from other types is the silence. There’s no cramping, no bleeding, no obvious warning. You may still feel pregnant because the placenta can continue producing hormones even after the embryo has stopped growing. Most people learn about a missed miscarriage only at a routine ultrasound, when no heartbeat is detected.
Chromosomal Errors Are the Leading Cause
When researchers analyze the genetic material of embryos from missed miscarriages, about 64.8% have chromosomal abnormalities. For comparison, only 3.9% of embryos from other types of miscarriage show these same errors. This means missed miscarriages are disproportionately tied to genetic problems in the embryo itself, not to anything the mother did or didn’t do.
These abnormalities typically happen during the earliest cell divisions after fertilization. An embryo might end up with too many or too few chromosomes, or with structural defects in its DNA that make continued development impossible. When this happens, the embryo either stops growing very early or never forms properly inside the gestational sac (sometimes called a blighted ovum). Because these are random errors in cell division, they’re largely unpredictable and unpreventable.
Why the Body Doesn’t Recognize the Loss
In a typical miscarriage, falling hormone levels trigger the uterus to contract and pass the pregnancy tissue. In a missed miscarriage, this signal gets delayed or disrupted. The placental tissue, even without a viable embryo, can keep producing hormones like hCG and progesterone for days or weeks. Progesterone in particular works to keep the uterine muscles relaxed and suppresses the immune response that would otherwise reject the pregnancy tissue. As long as progesterone levels remain high enough, the body stays in “pregnancy mode,” which is why symptoms like nausea or breast tenderness can persist.
Eventually hormone levels do drop, and the body will usually recognize the loss on its own. But this process can take weeks, and during that time many people have no idea anything has gone wrong.
Maternal Age and Miscarriage Risk
Age is one of the strongest predictors of miscarriage risk overall, and that includes missed miscarriages. A large registry-based study published in The BMJ found a clear J-shaped pattern: miscarriage risk is lowest at age 27 (about 9.5%), rises modestly through the early 30s, and then climbs steeply. By age 45 and older, the risk reaches 53.6%. Women under 20 also face a slightly elevated risk at 15.8%.
The age connection traces back to egg quality. As eggs age, they become more prone to the chromosomal division errors described above. This is why older maternal age increases the risk of not just miscarriage in general but missed miscarriage specifically, since chromosomal problems are the dominant cause of this type of loss.
Health Conditions That Raise the Risk
Beyond chromosomal factors and age, several maternal health conditions can contribute to missed miscarriage. These don’t cause the majority of cases, but they meaningfully increase the odds:
- Thyroid disorders. Both an overactive and underactive thyroid can disrupt the hormonal environment needed to sustain early pregnancy. The thyroid helps regulate metabolism and energy processes in the uterus, and imbalances can interfere with embryo implantation and growth.
- Uncontrolled diabetes. Poorly managed blood sugar creates a hostile environment for early embryonic development. The risk is tied to blood sugar control, not to having diabetes itself, which is why preconception management matters.
- Autoimmune conditions. Disorders like lupus can cause the immune system to attack the pregnancy tissue or disrupt blood flow to the developing placenta.
- Blood clotting disorders. Conditions that cause abnormal clotting can block the tiny blood vessels supplying the placenta, cutting off nutrients and oxygen to the embryo.
In many of these cases, the embryo may initially develop normally but fails because the uterine environment can’t support continued growth. The placenta may develop what’s called placental insufficiency, where it can’t produce adequate hormones or deliver sufficient blood flow. When hCG production drops, progesterone and estrogen follow, eventually destabilizing the pregnancy.
How a Missed Miscarriage Is Diagnosed
Because there are no outward symptoms, missed miscarriages are diagnosed by ultrasound. A doctor looks for specific signs: a gestational sac with no embryo inside, or an embryo that measures at a certain size but has no detectable heartbeat. When findings are borderline, a follow-up ultrasound is typically scheduled one to two weeks later to confirm the diagnosis and rule out the possibility that dates were simply off.
Blood tests measuring hCG levels can also help. In a healthy early pregnancy, hCG roughly doubles every two to three days. Levels that plateau or decline suggest the pregnancy is no longer progressing, though ultrasound remains the definitive diagnostic tool.
What Happens After Diagnosis
Once a missed miscarriage is confirmed, there are three paths forward: waiting for the body to pass the tissue naturally, using medication to speed the process, or a surgical procedure.
Expectant management (waiting) works for some people, but the timeline is unpredictable. It can take days to weeks for the body to complete the process, and there’s a risk of complications the longer tissue remains in the uterus. These include heavy bleeding that leads to anemia, infection that can damage reproductive organs or in rare cases progress to sepsis, chronic pelvic pain, and scarring inside the uterus known as Asherman’s syndrome.
Medication, typically a drug called misoprostol, prompts the uterus to contract and expel the tissue. Success rates range from 77% to 92% depending on how the medication is given, with about 78.5% of patients achieving complete evacuation confirmed by ultrasound in one study. The process involves cramping and heavy bleeding, usually over one to several days. About half of patients treated with medication are discharged from the hospital within one day, while roughly 14% need stays of four or more days.
Surgical evacuation (a D&C procedure) has the highest success rate at about 95%. It’s a brief outpatient procedure, and most people go home the same day. Recovery typically involves a few days of mild cramping and light bleeding. Some people choose this option because it offers the fastest resolution and the most certainty that the process is complete. It also allows the tissue to be sent for genetic testing, which can provide answers about whether a chromosomal abnormality was the cause.
Why It Usually Isn’t Preventable
The hardest part for many people is accepting that a missed miscarriage, in most cases, couldn’t have been avoided. When the cause is a chromosomal error in the embryo, no amount of rest, nutrition, or medical intervention would have changed the outcome. These are biological accidents during cell division.
For people with identifiable health conditions like thyroid disease or diabetes, optimizing treatment before conception can reduce the risk. And for those who experience recurrent miscarriages (three or more), specialized testing for clotting disorders, immune factors, and uterine abnormalities can sometimes uncover a treatable cause. But for a single missed miscarriage, the overwhelming likelihood is that it was caused by a one-time genetic error that won’t necessarily repeat in a future pregnancy.