Miscarriage is far more common than most people realize. About 10% of all clinically recognized pregnancies end in miscarriage, and for women in their 20s, the rate ranges from 9% to 17%. When you include very early losses that happen before a missed period, the true number is likely higher, since many of those pregnancies are never detected by a test.
Miscarriage Risk by Age
Maternal age is the single biggest factor in how likely a miscarriage is. For women between 20 and 30, roughly 9 to 17 out of every 100 recognized pregnancies end in loss. At 35, that number climbs to about 20%, or 1 in 5. By 40, the risk is 40%, and by 45 it reaches 80%.
This steep increase is largely driven by egg quality. As eggs age, they are more likely to have the wrong number of chromosomes, which makes a viable pregnancy less likely. Paternal age plays a role too, though a smaller one. A study of over 1,700 donor-egg fertility cycles found that when the father was older than 45, the miscarriage rate was about 24%, compared to 16% when he was 45 or younger. That’s a meaningful difference, roughly 1.6 times the risk, even when the eggs came from younger donors.
When Most Miscarriages Happen
The vast majority of miscarriages occur in the first trimester, before 13 weeks of pregnancy. The risk drops significantly once certain milestones are reached. Research on women with a history of recurrent loss shows that reaching six weeks of pregnancy gave a 78% chance of the pregnancy continuing. Once a heartbeat was visible on ultrasound at eight weeks, the chance of continuing rose to 98%. By ten weeks, it climbed to 99.4%.
These numbers come from a higher-risk group (women with previous losses), so for someone without that history, the odds after seeing a heartbeat are even more reassuring. Still, the pattern holds broadly: risk is highest in the earliest weeks and falls sharply as the pregnancy progresses.
The Most Common Cause
Chromosomal abnormalities cause about 50% of all first-trimester miscarriages. These are random errors that happen when the fertilized egg divides, resulting in too many or too few chromosomes. The embryo simply can’t develop normally. This type of loss is not caused by anything the parent did or didn’t do, and in most cases it’s a one-time event that doesn’t predict future pregnancies.
The other half of early losses stem from a mix of factors, including hormonal imbalances, uterine abnormalities, immune system issues, and infections. In some cases, no specific cause is ever identified.
Medical Conditions That Raise Risk
Several underlying health conditions are linked to higher miscarriage rates. The most well-established include:
- Thyroid disease: Both autoimmune thyroid problems and even mild underactive thyroid function are strongly associated with miscarriage and preterm birth.
- Polycystic ovary syndrome (PCOS): Women with PCOS who also have insulin resistance face elevated miscarriage rates. Insulin resistance on its own is considered an independent risk factor.
- Diabetes and poor blood sugar control: Consistently high blood sugar can cause problems with placental development, increasing the chance of loss at various stages of pregnancy.
- Low progesterone: Insufficient progesterone in the second half of the menstrual cycle can prevent the uterine lining from supporting implantation, contributing to recurrent loss.
Many of these conditions are manageable with treatment, which is one reason that evaluation after recurrent losses can be so valuable. Identifying and addressing an underlying hormonal issue can meaningfully change outcomes in a future pregnancy.
Recurrent Miscarriage Is Less Common
While a single miscarriage is very common, experiencing repeated losses is not. Fewer than 5% of women will have two consecutive miscarriages, and only about 1% experience three or more in a row. Having one miscarriage does not significantly raise your odds of having another. Most people who miscarry go on to have a healthy pregnancy afterward.
When losses do recur, it often prompts testing for treatable causes like hormonal imbalances, blood clotting disorders, or structural issues with the uterus. Recurrent pregnancy loss, defined as two or more consecutive losses, affects roughly 1 to 2% of couples worldwide.
Racial Disparities in Pregnancy Loss
Not everyone faces the same level of risk. CDC data from 2015 to 2017 shows that Black women experienced stillbirth (fetal death after 20 weeks) at more than twice the rate of white and Hispanic women: 11.2 per 1,000 compared to about 5.0. Black mothers also had substantially higher rates of pregnancy loss linked to pre-existing health conditions and placental complications.
These disparities aren’t explained by biology alone. Differences in access to quality healthcare, preconception health, socioeconomic stress, and the documented effects of institutional racism all contribute. Hispanic women also showed elevated rates of loss related to pregnancy complications and diabetes compared to white women, though the gap was narrower than for Black women.
Losses Before You Know You’re Pregnant
The 10% figure covers pregnancies that are clinically recognized, meaning a positive pregnancy test or ultrasound confirmation. But a significant number of pregnancies end before a person even misses a period. These are sometimes called chemical pregnancies: a fertilized egg implants briefly, may produce just enough hormone to trigger a faint positive test, and then is lost within days. Because most of these go unnoticed, exact numbers are hard to pin down, but some estimates suggest the total rate of all conception losses, including these very early ones, is considerably higher than what clinical statistics capture.
The widespread use of highly sensitive home pregnancy tests means more people are now detecting pregnancies earlier than in past decades. This can mean more awareness of very early losses that previously would have been experienced as a slightly late or heavy period.