About 1 in 6 recognized pregnancies ends in miscarriage, with a pooled risk of roughly 15% across all age groups. That number, drawn from a large Lancet analysis, only counts pregnancies that were confirmed through a test or ultrasound. When you include very early losses that happen before a person even knows they’re pregnant, the total is closer to 1 in 4.
The Overall Numbers
The American College of Obstetricians and Gynecologists puts the rate of clinically recognized early pregnancy loss at about 10%. A broader Lancet review, which pooled data from studies worldwide, found a rate of 15.3%. The gap between those figures comes down to how “recognized” is defined and which populations were studied, but either way, miscarriage is one of the most common outcomes in human reproduction.
Around 80% of all miscarriages happen in the first trimester, before 13 weeks. Very early losses, sometimes called chemical pregnancies, account for a large share. These occur when a fertilized egg implants briefly enough to trigger a positive pregnancy test but doesn’t continue developing. A person might experience what seems like a late, heavy period and never realize a pregnancy began at all. When these losses are counted, roughly 25% of all pregnancies end within the first 20 weeks.
How Risk Changes Week by Week
The chance of losing a pregnancy is highest in the earliest weeks and drops steadily as the pregnancy progresses. A study tracking over 12,000 pregnancies found that the weekly risk of miscarriage peaked at around 4% at or before six weeks from the last menstrual period. By week 8, the risk per week had fallen to about 3%. At week 12 it was roughly 1%, and by weeks 13 through 19 it dropped below 0.5%.
This is why seeing a heartbeat on an early ultrasound is reassuring but not a guarantee, while reaching the second trimester represents a genuine shift in risk. For most people, once a pregnancy passes the 12-week mark, the odds of carrying to term are very high.
Age Is the Strongest Risk Factor
Maternal age has a larger effect on miscarriage risk than almost any other single factor. For women between 20 and 30, the chance of miscarriage in any given pregnancy is about 9% to 17%. At 35 it rises to roughly 20%, or 1 in 5. At 40 it reaches 40%. And by 45, the risk climbs to around 80%.
The reason is primarily egg quality. As a person ages, eggs are more likely to have the wrong number of chromosomes. When an embryo has too many or too few chromosomes, it usually cannot develop normally, and the pregnancy ends on its own. This isn’t something a person can prevent through lifestyle changes; it’s a built-in feature of reproductive biology.
The father’s age matters too, though less dramatically. A study of nearly 14,000 women found that pregnancies conceived with fathers aged 40 or older had about 60% higher odds of miscarriage compared to those with fathers aged 25 to 29, even after accounting for the mother’s age. Researchers have described this as a slight increase in risk for any individual couple, but it’s statistically real across large populations.
Why Most Miscarriages Happen
At least half of all first-trimester miscarriages are caused by chromosomal abnormalities in the embryo. These are random errors that occur when egg and sperm cells divide and combine. They’re not inherited conditions and they don’t reflect anything the parents did wrong. The embryo simply received a set of genetic instructions that couldn’t produce a viable pregnancy.
Other causes include problems with the uterine lining, hormonal imbalances, blood clotting disorders, uncontrolled chronic conditions like diabetes or thyroid disease, and structural differences in the uterus. Infections and immune system factors can also play a role. But in a large number of cases, especially one-time losses, no specific cause is ever identified. That uncertainty can be one of the hardest parts of the experience.
Risk After Previous Losses
Having one miscarriage does not mean future pregnancies are doomed. After a single miscarriage, the risk of another one is about 20%, which is only modestly higher than the baseline risk for the general population. After two consecutive miscarriages, the risk rises to about 25%. After three or more in a row, it reaches 30% to 40%.
Those numbers also mean that even after three consecutive losses, the majority of people will go on to have a successful pregnancy. Recurrent miscarriage, defined as two or more consecutive losses, affects a smaller subset of people and sometimes points to a treatable underlying condition like a blood clotting disorder, a uterine abnormality, or a hormonal issue. Testing is typically offered after two or three losses to look for these causes.
Disparities in Pregnancy Loss
Not everyone faces the same risk. While most of the available data on racial disparities focuses on stillbirth (loss after 20 weeks) rather than earlier miscarriage, those numbers reveal significant gaps. Black women in the U.S. experience fetal mortality at more than twice the rate of white and Hispanic women: 11.2 per 1,000 compared to about 5.0 per 1,000. Contributing factors include differences in preconception health, access to quality care, socioeconomic conditions, chronic stress, and the effects of systemic racism on health outcomes.
Women under 20 and over 40 also face elevated rates of fetal loss, and carrying multiples (twins, triplets) more than doubles the risk of a fetal death compared to singleton pregnancies. These patterns reinforce that pregnancy loss is shaped by biology, but also by the circumstances surrounding a pregnancy.
What the Numbers Mean in Practice
If you’ve had a miscarriage, the statistics can feel both comforting and cold. Knowing that 1 in 4 or even 1 in 6 pregnancies ends this way doesn’t erase the grief, but it does make clear that miscarriage is overwhelmingly common and overwhelmingly not your fault. The single most common cause is a random genetic error that no amount of rest, prenatal vitamins, or careful behavior could have prevented.
For people planning a pregnancy after a loss, the data is genuinely encouraging. The vast majority of those who miscarry once go on to have healthy pregnancies. Even after multiple losses, the odds still favor a successful outcome, particularly when underlying conditions are identified and treated.