About 10 to 15 percent of clinically recognized pregnancies end in miscarriage. When you include pregnancies that end before a person even knows they’re pregnant, the number rises to roughly 30 percent of all conceptions. These figures make miscarriage the most common complication of pregnancy, yet many people are surprised by how frequently it happens.
A miscarriage is defined as a pregnancy loss before 20 weeks of gestation. After that threshold, the loss is classified as a stillbirth.
Why the Numbers Vary So Much
You’ll see miscarriage statistics ranging from 10 percent to 30 percent depending on what’s being counted. The lower figure, roughly 10 to 15 percent, reflects pregnancies that were confirmed through a blood test, urine test, or ultrasound. The higher estimate, around 30 percent of all conceptions, accounts for what are sometimes called chemical pregnancies: fertilized eggs that implant briefly, may cause a faint positive on a home test or a late period, and then are lost within days. Many people experience these losses without ever realizing a pregnancy began.
Modern home pregnancy tests can detect a pregnancy earlier than ever before, which means more chemical pregnancies are being noticed now than in previous decades. This can make it seem like miscarriage rates are rising when, in reality, more very early losses are simply being identified.
How Risk Changes Week by Week
The risk of miscarriage drops sharply as a pregnancy progresses. At six weeks of gestation, the risk is about 9.4 percent. By eight weeks, it falls to around 1.5 percent. Once a heartbeat is confirmed on ultrasound, typically between six and eight weeks, the odds of carrying to term improve significantly.
The vast majority of miscarriages happen in the first trimester, before 13 weeks. Second-trimester losses (between 13 and 20 weeks) are far less common, occurring in roughly 1 to 5 percent of pregnancies. By the time you reach the second trimester, the highest-risk window has passed.
What Causes Most Miscarriages
Chromosomal abnormalities cause about 50 percent of all first-trimester miscarriages. These are random errors that occur when the fertilized egg’s cells divide. The embryo ends up with too many or too few chromosomes, making normal development impossible. This type of loss is not caused by anything either parent did or didn’t do.
Other factors that can contribute include hormonal imbalances, problems with the structure of the uterus, infections, chronic conditions like uncontrolled diabetes or thyroid disease, and autoimmune disorders that affect blood clotting. Lifestyle factors like smoking, heavy alcohol use, and certain drug use also increase risk. But for most people who experience a single early miscarriage, no specific cause is ever identified, and the pregnancy loss is considered a chance event.
How Maternal Age Affects Risk
Age is the single biggest factor influencing miscarriage risk, and the numbers shift dramatically after 35. According to Cleveland Clinic data, the breakdown looks like this:
- Ages 20 to 30: 9 to 17 percent chance of miscarriage
- Age 35: about 20 percent (1 in 5)
- Age 40: about 40 percent (4 in 10)
- Age 45: about 80 percent (8 in 10)
The steep increase after 40 is driven largely by the same chromosomal issues that cause most early losses. As eggs age, errors during cell division become more frequent. This is a biological reality, not a reflection of overall health or fitness.
Paternal Age Matters Too
The age of the sperm-producing partner also plays a role, though it gets far less attention. A study published in Human Reproduction found that when the father was over 45, the miscarriage rate was 23.8 percent compared to 16.3 percent when the father was 45 or younger. Even after adjusting for other variables, advanced paternal age was associated with a 61 percent higher odds of miscarriage. Sperm accumulate genetic mutations over time, which can affect embryo viability in ways similar to egg aging.
Risk After Previous Miscarriages
One of the most common fears after a miscarriage is that it will happen again. The numbers here are more reassuring than many people expect. After one miscarriage, the risk of another is about 20 percent, meaning you still have roughly an 80 percent chance of a successful pregnancy next time. After two consecutive losses, the risk rises to about 25 percent. Even after three or more miscarriages in a row, the chance of another loss is 30 to 40 percent, which still leaves a majority chance of carrying to term.
Recurrent miscarriage, typically defined as three or more consecutive losses, affects about 1 percent of couples trying to conceive. At that point, testing for underlying causes like clotting disorders, uterine abnormalities, or hormonal issues becomes standard. Many of these causes are treatable, and most people with recurrent loss do eventually have a successful pregnancy.
Why Miscarriage Feels More Isolating Than It Should
Despite affecting roughly one in four or five known pregnancies, miscarriage remains something many people experience in silence. The tradition of waiting until 12 weeks to announce a pregnancy, while well-intentioned, can leave those who miscarry feeling like they’re grieving alone because few people knew the pregnancy existed. The reality is that miscarriage is extraordinarily common, it is almost never caused by something the pregnant person did wrong, and the odds of a healthy pregnancy afterward remain strongly in your favor.