Roughly 10% to 20% of all known pregnancies end in miscarriage, with the most commonly cited figure falling around 15%. That number only counts pregnancies a person already knows about. Many losses happen so early that they’re mistaken for a late period, which means the true rate is almost certainly higher.
How Risk Changes Week by Week
About 80% of all miscarriages happen within the first 12 weeks of pregnancy. The risk is highest in the earliest weeks: at six weeks or earlier, the weekly probability of loss is around 4%. By eight weeks, it drops to roughly 3%. By twelve weeks it falls to about 1.3%, and after 13 weeks the chance dips below 0.5% per week. Each passing week with a confirmed heartbeat meaningfully lowers the odds.
This steep decline is one reason early pregnancy can feel so anxiety-filled. The reassurance is real, though: once you’ve seen a heartbeat on ultrasound and reached the second trimester, the vast majority of pregnancies continue normally.
Why Most Early Miscarriages Happen
More than half of early pregnancy losses are caused by random chromosomal problems in the embryo. The fertilized egg ends up with too many or too few chromosomes, or pieces of chromosomes get rearranged in ways that prevent normal development. This is essentially a biological lottery that happens at the moment of conception, not something caused by stress, exercise, or anything a person did or didn’t do.
Other contributing factors include hormonal imbalances, uterine structural issues, blood clotting disorders, and poorly controlled chronic conditions like diabetes or thyroid disease. But for a single, isolated miscarriage, the cause is most often chromosomal and unlikely to repeat.
The Role of Maternal Age
Age is the single biggest factor affecting miscarriage risk, and the numbers shift substantially after 35. In studies tracking pregnancies confirmed by ultrasound, the miscarriage rate breaks down roughly like this:
- Under 35: below 15%
- Around 40: approximately 29%
- At 44: around 60%
- Over 44: higher still
The reason ties back to chromosomes. As eggs age, the cellular machinery that divides chromosomes evenly becomes less reliable. The older the egg, the more likely an embryo will have a chromosomal imbalance that makes it nonviable. This isn’t a reflection of overall health; it’s a basic feature of egg biology.
Paternal Age Matters Too
The father’s age gets far less attention, but it plays a measurable role. A study published in Human Reproduction compared pregnancy outcomes when the father was over 45 to outcomes when the father was 45 or younger. The miscarriage rate was 23.8% in the older group versus 16.3% in the younger group. After adjusting for other variables, fathers over 45 had about 60% higher odds of a pregnancy ending in miscarriage. Sperm accumulates DNA damage over time, which can contribute to embryos that don’t develop normally.
Risk After a Previous Miscarriage
Having one miscarriage does not dramatically change your odds for the next pregnancy. According to the Mayo Clinic, the risk breaks down this way:
- After one miscarriage: about 20% chance of another (only slightly above the baseline)
- After two consecutive miscarriages: about 25%
- After three or more in a row: 30% to 40%
Even after three consecutive losses, the odds still favor a successful pregnancy. Recurrent miscarriage (typically defined as two or three losses in a row) does warrant investigation, because treatable causes like clotting disorders or uterine abnormalities become more likely in that group. But the majority of people who experience a single loss go on to have a healthy pregnancy next time.
Racial Disparities in Pregnancy Loss
Most miscarriage statistics don’t break down neatly by race because national surveillance data only captures fetal deaths after 20 weeks (stillbirths). But those later-pregnancy numbers reveal stark gaps. CDC data from 2015 to 2017 shows that Black women experienced fetal death at a rate of 11.2 per 1,000 pregnancies, more than double the rate among white women (5.0) and Hispanic women (5.1).
The disparity isn’t explained by genetics. Black mothers had significantly higher rates of pregnancy loss tied to pre-existing maternal health conditions and pregnancy complications, including placental and umbilical cord problems. These patterns reflect broader inequities in healthcare access, chronic disease management, and the quality of prenatal care. Congenital malformations, by contrast, showed no significant racial differences.
How Miscarriage Is Confirmed
If you’re experiencing bleeding or cramping in early pregnancy, a single ultrasound doesn’t always give a definitive answer. Doctors look for specific markers: whether an embryo is visible inside the gestational sac, whether a heartbeat is detectable, and how large the sac and embryo are. A small or empty sac on an early scan can simply mean the pregnancy is earlier than expected.
Because of this uncertainty, a follow-up ultrasound at least seven days later is common. If the sac was empty on the first scan and still shows no embryo or yolk sac on the second, that consistently confirms a loss. The waiting period between scans can be agonizing, but it exists to prevent misdiagnosis of a pregnancy that’s simply too early to see clearly.
The Numbers People Don’t Talk About
The 10% to 20% figure only captures losses that happen after a positive pregnancy test or missed period. Research using sensitive hormone testing suggests that up to 30% to 50% of all fertilized eggs never make it to a clinical pregnancy. They fail to implant or stop developing within days, often before a person has any idea conception occurred. In practical terms, this means pregnancy loss is one of the most common events in human reproduction, and the vast majority of the time, a single miscarriage carries no long-term implications for fertility.