An estimated 750,000 to 1 million clinically recognized miscarriages occur in the United States each year. That figure is based on the roughly 10% to 20% of known pregnancies that end in loss before 20 weeks of gestation, applied to the approximately 3.6 million annual births. The true number is almost certainly higher, because many pregnancies end before a person ever realizes they’ve conceived.
Why the True Number Is Hard to Pin Down
The 10% to 20% figure cited by both the Mayo Clinic and March of Dimes only counts pregnancies that were already confirmed, typically through a positive home test or a doctor’s visit. But a large share of pregnancies fail in the earliest days, sometimes before a missed period even registers. These very early losses, often called chemical pregnancies, happen when a fertilized egg implants briefly enough to trigger a faint positive test but stops developing within days. About 25% of all pregnancies end within the first 20 weeks, and roughly 80% of those losses occur very early. Some researchers estimate that more than 30% of all conceptions end in miscarriage when these earliest losses are included.
Because so many of these losses go undetected or unreported, the United States has no centralized registry that tracks every miscarriage. Hospitals and clinics are not required to report pregnancy losses before 20 weeks to vital statistics offices. That reporting threshold is the dividing line: losses before 20 weeks are classified as miscarriages, while losses at 20 weeks or later are classified as stillbirths and are tracked through death certificates.
When Most Miscarriages Happen
The vast majority of miscarriages, about 80%, occur in the first trimester, before the 12th week of pregnancy. The risk drops steeply as the weeks progress. By around 16 to 20 weeks, the weekly rate of loss levels off to a very low baseline of roughly 0.3 per 100 ongoing pregnancies per week. Once a heartbeat is confirmed on ultrasound, typically around 6 to 7 weeks, the overall odds of carrying to term rise significantly.
The Leading Cause Is Chromosomal
Most first-trimester miscarriages are caused by chromosomal abnormalities in the embryo. Depending on the study, somewhere between 40% and 76% of early losses involve the wrong number of chromosomes, a random error during cell division that prevents normal development. This is not something either parent can prevent. It is essentially a biological quality-control process: the pregnancy stops progressing because the embryo was never viable.
The rate of chromosomal problems in miscarriages climbs with the age of the egg. Among women aged 23 to 37, roughly 55% to 65% of miscarried tissue shows abnormal chromosomes. After 37, that proportion rises sharply. By age 44, chromosomal abnormalities account for more than 90% of losses. A study of over 7,000 miscarriage cases identified age 37 to 38 as the point where the rate of chromosomally abnormal losses jumps most dramatically, from about 64% to 79%.
How Risk Changes With Age
Maternal age is the single strongest predictor of miscarriage risk. The numbers shift substantially across a woman’s reproductive years:
- Ages 20 to 30: 9% to 17% chance of miscarriage
- Age 35: about 20%, or 1 in 5 pregnancies
- Age 40: about 40%, or 4 in 10 pregnancies
- Age 45: about 80%, or 8 in 10 pregnancies
These numbers reflect the increasing likelihood of chromosomal errors in eggs as they age. They are population-level averages, not individual guarantees. Plenty of people over 35 carry healthy pregnancies to term, but the statistical reality is that the odds of loss roughly double between 30 and 40.
Racial Disparities in Pregnancy Loss
Pregnancy loss does not affect all communities equally. Most of the detailed tracking applies to stillbirths (losses at 20 weeks or later), but the patterns reveal significant gaps. During 2015 to 2017, Black women experienced fetal deaths at a rate of 11.2 per 1,000 births, more than double the rate among White women (5.0) and Hispanic women (5.1). Black mothers had substantially higher rates of loss linked to pre-existing health conditions and pregnancy complications, roughly three times the rate of White mothers in both categories.
Hispanic mothers also faced elevated risks in certain areas, particularly losses related to diabetes-related conditions during pregnancy, at about twice the rate of White mothers. These disparities reflect broader inequities in access to prenatal care, chronic disease burden, and the quality of care received during pregnancy.
Stillbirth Numbers: What the CDC Tracks
While miscarriages before 20 weeks go largely uncounted in official records, the CDC does track fetal deaths from 20 weeks onward. In 2024, there were an estimated 19,756 stillbirths in the United States, down slightly from 20,005 in 2023 and 20,202 in 2022. The overall fetal mortality rate was 5.41 per 1,000 births in 2024, a modest 2% decline from the year before. Late fetal deaths (at 28 weeks or beyond) saw the largest improvement, dropping 4% between 2023 and 2024.
These roughly 20,000 annual stillbirths are separate from, and in addition to, the estimated 750,000-plus miscarriages that happen earlier in pregnancy. Combined, they represent a significant burden of pregnancy loss that touches hundreds of thousands of families each year.
Other Factors That Raise Risk
Beyond age and chromosomal chance, several other factors increase the likelihood of miscarriage. Chronic conditions like uncontrolled diabetes, thyroid disorders, and autoimmune diseases can interfere with early pregnancy. Uterine abnormalities, such as fibroids or a septum dividing the uterine cavity, sometimes prevent proper implantation or blood supply. Smoking, heavy alcohol use, and certain infections also raise risk.
Having one miscarriage does not meaningfully change your odds for the next pregnancy. Most people who experience a single loss go on to have a healthy pregnancy afterward. Recurrent miscarriage, defined as three or more consecutive losses, affects about 1% to 2% of couples and typically prompts testing for underlying causes like blood-clotting disorders, hormonal imbalances, or structural issues in the uterus.