Approximately 10-15% of known pregnancies end in miscarriage before week 13, with about 80% of all pregnancy losses occurring during the first trimester, according to the Office on Women's Health and March of Dimes. This means most miscarriages happen in the earliest weeks when you're least likely to have shared the news.
But numbers alone don't tell you what's normal for your situation. Your age, how far along you are, and whether you've detected a fetal heartbeat all shift these odds significantly. Understanding the week-by-week breakdown—not just the overall percentage—helps separate typical early loss from patterns that warrant medical investigation.
Table of Contents
- The Big Picture: Overall Miscarriage Rates
- First Trimester Week by Week: When Risk Is Highest
- After a Fetal Heartbeat: How the Odds Change
- The Second Trimester and Beyond: Lower but Present Risk
- How Your Age Affects Your Miscarriage Risk
- Recurrent Miscarriage: When Losses Happen Multiple Times
- What Causes Miscarriage: The Role of Chromosomal Abnormalities
- Understanding the Data Gap: Why Statistics Vary
- Risk Factors Beyond Age: What Increases Miscarriage Risk
- When to Call Your Doctor: Signs That Warrant Evaluation
- Frequently Asked Questions
The Big Picture: Overall Miscarriage Rates
The most commonly cited statistic comes from March of Dimes research: 10-15% of pregnancies known to be pregnancies end in loss before week 13. The phrase "known to be" matters. The true rate of loss—including pregnancies that end before a positive test—is believed to be higher, but there's no official count because the CDC does not collect federal statistics on losses before 20 weeks.
about 80% of all miscarriages occur in the first trimester. This clustering in early weeks reflects the biology: most miscarriages result from chromosomal problems that prevent normal development. A pregnancy that makes it past week 13 faces dramatically lower risk going forward. The term "miscarriage" refers to any loss before 20 weeks of pregnancy.
After week 20, a loss is termed "stillbirth." This distinction matters for statistics, because different agencies track different timeframes. When you read a statistic, check whether it covers losses through 13 weeks, 20 weeks, or all recognized pregnancies—the numbers change significantly depending on the window. That 10-15% figure is often quoted as the baseline risk for any pregnancy.
But your actual risk depends on specific details: how far along you are right now, your age, whether you've seen a heartbeat, and whether you have a history of previous losses. These details can move your personal risk substantially up or down from the population average. Most people who experience a miscarriage go on to have successful subsequent pregnancies.
Even after one loss, the chance of another loss is not dramatically higher than it was before. This optimistic baseline is worth keeping in mind when you're reading risk statistics that otherwise might feel alarming. Statistics come from several sources: prospective cohort studies following pregnancies from early on, clinical trial data, and hospital records. Because there's no mandatory federal registry, smaller studies and medical institutions provide most of our numbers. The March of Dimes and ACOG (American College of Obstetricians and Gynecologists) synthesize these to provide clinical guidance.
First Trimester Week by Week: When Risk Is Highest
Recent research gives us a clearer picture of how risk changes week to week. A 2025 pooled analysis examined over 12,000 pregnancies from six studies and found miscarriage risk was highest at 6 weeks or earlier from the last menstrual period (4%), dropped to 1.5% by week 8, and fell below 0.5% by weeks 13-19.
This shows risk is not distributed evenly—the earliest weeks carry the highest burden. At 6 weeks, many people have just discovered they're pregnant. That's also when miscarriage risk peaks at 4%—one in 25 pregnancies at that gestational age. Many of these losses happen before a clinical confirmation or before you've scheduled your first appointment.
Some occur so early that a person might mistake the miscarriage for a late period. By week 7, risk has already dropped to about 3%. By week 8, it's down to 1.5%. This rapid decline in the second and third weeks of pregnancy is important to know: if you're past week 8, your risk of miscarriage is already half what it was at week 6, even without other reassuring signs.
Weeks 9-10 see further improvement. By week 10, miscarriage risk is under 1%—far lower than it was just a few weeks earlier. The difference between week 6 and week 10 is dramatic: your risk drops by more than 75%. This is why the first ultrasound appointment is such a turning point emotionally—seeing an age-appropriate heartbeat means you've already passed the highest-risk window.
Weeks 11-13 (still technically the first trimester) carry miscarriage risk below 0.5%. By the time you reach your second trimester, most chromosomal abnormalities that would cause loss have already resulted in miscarriage if they were going to. Pregnancies that make it past week 13 are far more likely to continue. This week-by-week picture explains why "the first trimester" groups weeks with very different risk profiles.
The risk in week 6 is ten times higher than the risk in week 13, even though both are in the first trimester. When you hear "first trimester," understand the earliest weeks carry the highest burden.
After a Fetal Heartbeat: How the Odds Change
Seeing or hearing a fetal heartbeat is a significant reassurance because the presence of a heartbeat strongly predicts ongoing pregnancy. Once a fetal heartbeat is detected at around week 6, miscarriage risk drops to 9%; at week 7 it's 4%; at week 8, approximately 1.5%; and by weeks 9-10, it's under 1%.
These numbers are reassuring because they show that each passing week, especially with a confirmed heartbeat, meaningfully reduces your risk. The presence of a fetal heartbeat matters because it indicates the pregnancy has developed past the stage where most chromosomal problems manifest as loss. The heartbeat is a sign of normal organ development.
A viable heartbeat—one that's present and beating at a normal rate for the gestational age—is one of the strongest predictors of pregnancy continuation. Doppler ultrasound can detect a heartbeat starting around week 6, though it's more reliably visible by week 7. A transvaginal ultrasound (probe placed inside the vagina) can detect heartbeats earlier than an abdominal ultrasound.
Some clinicians use Doppler technology in the office; others refer to ultrasound for confirmation. The timing depends on your provider's protocol and how far along you are. Heartbeat rate also matters. A typical fetal heart rate at week 8-9 is 120-160 beats per minute. A rate significantly slower than this can sometimes signal concern, though a single low reading isn't necessarily predictive of outcome.
Your clinician will track heart rate over time if there's any question, because the trend matters more than a single number. Women who have seen a heartbeat and still miscarry sometimes worry they did something wrong. The presence of a heartbeat does not mean a loss is preventable. If chromosomal abnormalities emerge later in pregnancy, miscarriage can still occur even after a normal heartbeat was documented.
The heartbeat is reassuring, not a guarantee. Some clinicians offer serial ultrasounds in early pregnancy—scans spaced days or a week apart—to track heartbeat development and confirm normal progression. This is common if you've had previous losses or if there's uncertainty about dating. Serial ultrasounds provide reassurance over time and can catch concerning patterns early.
The Second Trimester and Beyond: Lower but Present Risk
Once you reach week 14 (the start of the second trimester), miscarriage risk drops to between 1-5%, according to March of Dimes and clinical literature reviews. This is a significant shift from first-trimester risk. But it's important to know: miscarriage can still happen in the second trimester, and the causes often differ from early losses.
Early second-trimester losses (weeks 14-19) most often result from chromosomal abnormalities that went undetected in the first trimester. Some structural problems—heart defects, kidney problems, neural tube defects—may not show their impact until later. Infections, placental problems, and uterine issues become more common causes as pregnancy advances. The 20-week threshold has medical significance. Before 20 weeks, a loss is classified as miscarriage.
After 20 weeks, it's classified as stillbirth. This distinction affects how your loss is managed medically and how statistics are tracked. Most miscarriage support and research focus on losses through 13-20 weeks. Losses in the second trimester are less common but often more emotionally difficult because they tend to happen after people have started feeling movement, shared the news, and begun preparing.
The miscarriage may require delivery (either medical or surgical management) rather than occurring at home. Recovery is longer and the grief process may be more complicated. Risk continues to decline through weeks 20-24 and into the third trimester. By week 28, miscarriage risk is very low—under 1%. Losses at this stage are typically called stillbirths rather than miscarriages and have different medical and emotional management.
The distinction is partly about viability—whether a baby born at that gestational age could survive with intensive care. If you're in the second trimester and have previously had normal ultrasounds and bloodwork, your risk is considerably lower than it was in the first trimester. Anatomy scans (usually offered around week 20) can detect many structural problems that would increase risk. Normal anatomy and normal bloodwork are significant reassurances at this stage.
How Your Age Affects Your Miscarriage Risk
Your age at conception significantly affects your personal miscarriage risk. Women aged 20-30 face a 9-17% miscarriage risk; at age 35, that risk is 20%; at age 40, it's 40%; and at age 45, it reaches 80%, according to ACOG guidelines. This age-related increase is primarily due to older eggs being more likely to have chromosomal abnormalities.
At age 20-25, miscarriage risk is on the lower end of the range. By age 30, it's risen slightly to around 10-12%. These younger ages all fall well within the baseline population risk and don't warrant any special medical interventions beyond routine prenatal care. At age 35, a key medical milestone, miscarriage risk has risen to about 20%—a noticeable increase from age 30.
Age 35 is when ACOG recommends that genetic screening be offered to all pregnant people, not just those with family history. The risk isn't prohibitively high, but it's high enough that testing options become part of standard counseling. At age 40, the jump is more dramatic: 40% of pregnancies miscarry. This doesn't mean 40% of births end in loss—many pregnancies never implant, and these chemical pregnancies aren't always counted.
But for diagnosed pregnancies, the miscarriage rate is substantially higher. Genetic testing becomes even more important, and some people choose preimplantation genetic testing (PGT) when using IVF to screen embryos before transfer. At age 45, the miscarriage rate reaches approximately 80%. At this age, most chromosomal abnormalities are Down syndrome (trisomy 21), trisomy 18, or trisomy 13.
The biological reality is that continuing pregnancy becomes statistically unlikely, though it's not impossible. These statistics apply to your age at the time of conception, not your age now. If you're 40 and currently 12 weeks pregnant, your risk was determined by your age when you conceived, not by your current age. Many people delay diagnosis testing until weeks 12-15 to allow time to confirm viability before undergoing invasive testing.
Recurrent Miscarriage: When Losses Happen Multiple Times
About 2% of pregnant women experience recurrent miscarriage—defined as two or more consecutive losses, according to March of Dimes. This is different from the baseline population risk. If you've had one miscarriage, your risk of a second is not dramatically elevated. But if you've had two or three losses, medical evaluation is warranted.
The technical definition usually means two consecutive losses, though some clinicians wait for three before starting investigation. The reason for this threshold is that three consecutive losses occur by chance alone in about 1% of the population. Below three, identifying a specific cause becomes harder, and testing may not change management. Causes of recurrent miscarriage include chromosomal abnormalities in one parent (balanced translocation), blood clotting disorders, uterine anatomical problems (septum, fibroids), thyroid disease, and hormonal problems.
Some couples face idiopathic recurrent loss—meaning no specific cause is found despite testing. This doesn't mean nothing's wrong; it means the cause isn't captured by current testing. If you've experienced recurrent loss, your clinician should take you through a workup. This typically includes karyotyping (chromosomal analysis) of both partners, blood clotting studies, thyroid tests, imaging of the uterus (ultrasound or hysterosalpingography), and sometimes genetic counseling.
Some women with blood clotting disorders benefit from anticoagulation therapy in pregnancy. Having a history of recurrent loss changes your medical management in the next pregnancy. You may be offered more frequent ultrasounds, earlier testing, specialized care from a maternal-fetal medicine specialist, or specific treatments based on what was identified. Support groups exist specifically for people navigating recurrent loss.
Finding a cause reduces the psychological burden significantly. Even if the cause doesn't lead to treatment, knowing why the losses happened is emotionally different from facing the losses without explanation. Genetic counselors and reproductive endocrinologists can help interpret results and discuss implications for future pregnancies.
What Causes Miscarriage: The Role of Chromosomal Abnormalities
Chromosomal abnormalities are the most common cause of miscarriage across all gestational weeks, according to the Office on Women's Health and clinical studies. These abnormalities mean the baby has too many or too few chromosomes, or chromosomes with missing or extra pieces. The pregnancy cannot develop normally, and miscarriage typically results.
About half of first-trimester miscarriages involve chromosomal problems. The most common abnormalities are trisomy 21 (Down syndrome), trisomy 18, trisomy 13, and complete loss of a chromosome (monosomy X). These occur randomly during egg or sperm formation, usually not due to anything you did or didn't do. Maternal age increases the likelihood of chromosomal abnormalities in the egg.
Chromosomal problems are more common in early pregnancy losses and become proportionally more common with maternal age. A woman of 20 who miscarries has a lower chance that chromosomality was the cause compared to a woman of 45 miscarrying—because older eggs are simply more likely to have errors. Other causes of miscarriage include uterine anatomical problems (septate uterus, fibroids, scarring), infections, hormonal insufficiency, blood clotting disorders, and autoimmune conditions.
These account for a smaller proportion of early losses but become more common in second-trimester miscarriage. Lifestyle factors (smoking, heavy alcohol use, maternal age) increase miscarriage risk. Diet, exercise, coffee consumption, and stress have been studied but don't show strong causal relationships with miscarriage in the research literature. This doesn't mean you should ignore your health, but it does mean most miscarriages are not caused by something you could have prevented.
Infections can increase miscarriage risk, particularly certain sexually transmitted infections and untreated urinary tract infections. Chronic maternal illnesses like uncontrolled diabetes increase risk. Some medications increase risk; others do not. Your clinician should review your medication list and any health conditions that might affect pregnancy.
Understanding the Data Gap: Why Statistics Vary
The CDC does not collect federal statistics on pregnancy losses before 20 weeks, creating a significant data gap; most available statistics come from medical organizations, research institutions, and prospective cohort studies rather than government surveillance. This is why different sources sometimes cite different numbers. Prospective cohort studies follow pregnancies from early on and record outcomes systematically.
These are considered the most reliable source for miscarriage statistics because they don't rely on memory or retrospective reporting. A 2025 pooled analysis that examined data from six studies representing 12,390 pregnancies provides some of the most current week-by-week risk data available. Clinical trial data comes from trials studying fertility treatments, medications, or genetic conditions.
These studies weren't designed to measure miscarriage risk, but the data gets extracted and analyzed. This source has limitations: participants in trials don't represent the general population, and reporting standards vary. Hospital and insurance records provide another data source. Large insurance databases can track outcomes for hundreds of thousands of pregnancies. These are powerful for asking certain questions but miss home miscarriages and those managed outside the hospital system.
The lack of federal reporting means we don't know the true miscarriage rate in the United States. Some estimates suggest that including chemical pregnancies (losses before a positive test) and other very early losses, the true miscarriage rate might be 30-40% or higher. The 10-15% figure counts only diagnosed pregnancies that end in loss. Because there's no mandatory reporting, definitions vary.
Some studies define miscarriage as loss before 13 weeks; others use 20 weeks. Some include chemical pregnancies; others don't. When you're reading a statistic, checking the source and the definition is crucial. A seemingly simple number like "10% of pregnancies miscarry" becomes clearer when you know exactly what type of pregnancy and what stage of loss are being counted.
Risk Factors Beyond Age: What Increases Miscarriage Risk
Beyond age, several factors increase miscarriage risk enough to be clinically significant. Smoking increases risk by approximately 50%. Heavy alcohol use (more than five drinks per week) increases risk substantially. Uncontrolled maternal diabetes increases risk significantly. Untreated or inadequately treated thyroid disease increases risk. Uterine anatomical problems—a septate uterus (divided uterus), large fibroids, severe scarring from prior procedures—increase miscarriage risk.
Some of these problems are amenable to surgery before pregnancy, which can lower risk. Others require only careful monitoring. An anatomy imaging study can identify these problems. Thrombophilia (blood clotting tendency) increases miscarriage risk, particularly in the second trimester. Some women with blood clotting disorders who have recurrent loss benefit from anticoagulation therapy like low-molecular-weight heparin during pregnancy.
This requires diagnosis first—routine screening for thrombophilia isn't standard, but evaluation is offered after recurrent loss. Polycystic ovary syndrome (PCOS) may increase miscarriage risk slightly, though this remains debated in the literature. The reason isn't clear, though higher androgen levels and insulin resistance have been proposed. Management with metformin or other treatments may lower risk, but evidence isn't definitive.
Luteal phase defect—inadequate progesterone production in the second half of the cycle—was once thought to increase miscarriage risk and warrant supplementation. Current evidence doesn't support this theory, and routine progesterone supplementation isn't recommended for early pregnancy loss prevention in asymptomatic women. Previous miscarriage doesn't substantially increase your risk of future miscarriage, except when losses are recurrent (three or more).
Most people who miscarry once go on to have successful pregnancies. A single miscarriage is not predictive of future problems, though the emotional impact often makes the next pregnancy feel precarious.
When to Call Your Doctor: Signs That Warrant Evaluation
Vaginal bleeding, especially heavy bleeding or bleeding with clots, warrants a call to your clinician. Light spotting in the first trimester is relatively common and not always a sign of miscarriage, but bleeding should be evaluated. Your clinician can offer ultrasound or bloodwork to check for viability. Severe abdominal pain, cramping that doesn't ease with over-the-counter pain medication, or pain with vaginal bleeding should be evaluated urgently.
Pain can indicate miscarriage but also ectopic pregnancy or other problems. Don't wait—call your clinician or go to urgent care or the emergency room. Signs of incomplete miscarriage—heavy bleeding, passing clots or tissue, pain lasting more than a few hours—require medical evaluation. Your clinician may recommend ultrasound to confirm complete loss, or you may need medication or procedures to complete the process safely and reduce infection risk.
Fever during a suspected or confirmed miscarriage could indicate infection and warrants urgent care. Signs of infection include fever above 100.4°F, foul-smelling discharge, or severe pain. Infections after miscarriage can be serious, so don't dismiss this as typical grief-related symptoms. After miscarriage, heavy bleeding that soaks more than one pad per hour, passing clots larger than a golf ball, or symptoms lasting longer than a week should be reported.
These could indicate complications like retained tissue or infection that need treatment. Emotional distress after miscarriage is normal and expected. But if you're having thoughts of harming yourself, feel unable to function day-to-day, or can't stop thinking about the loss weeks or months later, reach out to a mental-health clinician. Pregnancy loss can trigger depression or anxiety that benefits from treatment.
Frequently Asked Questions
What percentage of pregnancies end in miscarriage?
Approximately 10-15% of known pregnancies end in miscarriage before week 13, with about 80% occurring in the first trimester. However, the true rate is believed to be higher when including losses that occur before a positive pregnancy test.
When is miscarriage risk highest?
Miscarriage risk is highest at 6 weeks of pregnancy (4%) and drops sharply through week 8 (1.5%), falling below 0.5% by week 13. Risk continues declining through the second trimester.
Does seeing a fetal heartbeat mean I won't miscarry?
Seeing a fetal heartbeat significantly reduces miscarriage risk—dropping to under 1% by weeks 9-10. However, miscarriage can still occur after a heartbeat is documented, though the risk is much lower. A confirmed heartbeat is one of the strongest predictors of pregnancy continuation.
How does my age affect my miscarriage risk?
Age substantially affects risk. Women aged 20-30 have a 9-17% miscarriage risk; at age 35, it rises to 20%; at age 40, to 40%; and at age 45, to 80%. The age-related increase is primarily due to chromosomal abnormalities in eggs becoming more common with age.
What causes most miscarriages?
Chromosomal abnormalities—having too many or too few chromosomes or chromosome pieces—are the most common cause of miscarriage across all gestational weeks. These occur randomly during egg or sperm formation, usually not due to anything a parent did or didn't do.
If I had one miscarriage, am I at higher risk for another?
Having one miscarriage does not substantially increase your risk of future miscarriage. Your baseline risk returns to what it was before the loss. However, if you experience three or more consecutive losses, medical evaluation for recurrent loss is recommended.
