Miscarriage Risk Calculator
Compare published miscarriage-risk figures by maternal age and by gestational week after a normal heartbeat scan, without combining different studies into false precision.
View published miscarriage-risk figures by maternal age and, after a normal ultrasound with fetal cardiac activity, by completed gestational week. The calculator keeps these studies separate rather than inventing a combined personal probability.
Published miscarriage-risk context
Use this miscarriage risk calculator to compare two published research findings: miscarriage risk by maternal age in a large population study, and miscarriage risk by completed gestational week after fetal cardiac activity was seen in an asymptomatic singleton pregnancy. The calculator deliberately keeps these results separate because the studies measured different populations and should not be blended into a single “personalized” probability.
Miscarriage risk by maternal age
A large Norwegian register study published in the BMJ analyzed 421,201 pregnancies from 2009 through 2013. After accounting for induced abortions as described by the researchers, overall miscarriage risk was 12.8%, but risk differed substantially by age.
| Maternal age | Published miscarriage risk |
|---|---|
| Under 20 | 15.8% |
| 20–24 | 11.3% |
| 25–29 | 9.8% |
| 30–34 | 10.8% |
| 35–39 | 16.7% |
| 40–44 | 32.2% |
| 45 and older | 53.6% |
This is the evidence used by the miscarriage risk calculator by age. It is a population statistic from all recognized pregnancies in that study, not a prediction for one pregnancy. The researchers found the lowest risk in ages 25–29 and a rapid increase after age 30.
Miscarriage risk calculator after heartbeat
A separate prospective study followed 696 asymptomatic women with a singleton pregnancy after fetal cardiac activity was seen at their first antenatal ultrasound. The risk of a subsequent miscarriage fell sharply with advancing gestation:
| Completed week at heartbeat scan | Published subsequent miscarriage risk | Pregnancy continued past 20 weeks |
|---|---|---|
| 6 weeks | 9.4% | 90.6% |
| 7 weeks | 4.2% | 95.8% |
| 8 weeks | 1.5% | 98.5% |
| 9 weeks | 0.5% | 99.5% |
| 10 weeks | 0.7% | 99.3% |
The 10-week figure is slightly higher than the 9-week figure in the published data. This calculator preserves the reported values rather than smoothing them into an artificial downward curve. The study was relatively small and should be interpreted as approximate group evidence.
Why the age and heartbeat percentages are not combined
The age study included hundreds of thousands of pregnancies from the general population. The heartbeat study included only asymptomatic women with one fetus and cardiac activity already seen on ultrasound. These are different starting populations. Multiplying or averaging the two percentages would create a number that neither study actually measured.
For that reason, the calculator may show an age-group figure and a post-heartbeat week figure side by side, but it never labels a blended number as “your miscarriage risk.” This is more defensible than a calculator that gives a highly precise percentage without a validated model covering all of the entered factors together.
Miscarriage risk calculator by week in the first trimester
The strongest week-specific evidence included here applies only after a normal scan has shown fetal cardiac activity and only for completed weeks 6 through 10. It should not be used to interpret a scan in which cardiac activity was not found, because timing, embryo size, scan type, and dating uncertainty can all matter.
ACOG notes that when cardiac activity is not detected, it may simply be too early, while in other circumstances it can indicate that a pregnancy has stopped developing. Ultrasound and sometimes serial hCG testing are used by clinicians to distinguish viable from nonviable pregnancy safely.
What symptoms mean for this calculator
The Tong heartbeat study recruited women who were asymptomatic at the visit. If you currently have bleeding or significant cramping, this calculator does not display that post-heartbeat percentage because the study population is not a good match. ACOG advises contacting an obstetric clinician for vaginal bleeding, fluid loss, passage of tissue, or concerning pain/cramping. Heavy bleeding or severe pain requires prompt medical evaluation.
Age, prior miscarriage, and other risk factors
The 2019 Norwegian study also found that previous miscarriage history was associated with higher risk in a later pregnancy. After adjustment for maternal age, the odds ratio was 1.54 after one prior miscarriage, 2.21 after two consecutive miscarriages, and 3.97 after three or more. Those are odds ratios rather than direct risk percentages, so this calculator does not convert them into an individualized probability without a validated model.
ACOG likewise identifies advanced maternal age and prior early pregnancy loss as important risk factors, while emphasizing that most early pregnancy loss is due to chromosomal abnormalities and is generally not caused by ordinary activities such as exercise, work, sex, stress, or past contraceptive use.
Frequently asked questions
How accurate is a miscarriage risk calculator?
It can accurately reproduce the published percentages from the studies it uses, but those population statistics cannot predict exactly what will happen in one pregnancy. Ultrasound findings, symptoms, medical history, pregnancy dating, and other clinical information matter.
What is the miscarriage risk after a heartbeat at 8 weeks?
In the Tong et al. prospective cohort of asymptomatic women with singleton pregnancies, the reported subsequent miscarriage risk at 8 completed weeks was 1.5%. That figure applies to the study population and is not a guarantee for an individual pregnancy.
Does miscarriage risk decrease each week?
In general, miscarriage risk falls as a viable pregnancy advances. In the heartbeat study used here, risk fell from 9.4% at 6 completed weeks to 0.5% at 9 weeks. The published 10-week estimate was 0.7%, slightly above 9 weeks because of sampling variation.
How does age affect miscarriage risk?
The Norwegian study reported 9.8% at ages 25–29, 16.7% at 35–39, 32.2% at 40–44, and 53.6% at age 45 or older. These are general population figures and should not be substituted for an individual clinical assessment.
Is this a miscarriage risk calculator first trimester tool?
Yes, the page is designed for first-trimester risk context. The heartbeat-specific study values shown by week apply to weeks 6–10 after cardiac activity was documented in asymptomatic singleton pregnancies.
Methodology and sources
The maternal-age table comes from Magnus et al., BMJ 2019, a prospective register-based analysis of 421,201 Norwegian pregnancies. The heartbeat-by-week table comes from Tong et al., Obstetrics & Gynecology 2008, which followed 696 asymptomatic women after fetal cardiac activity was documented. ACOG guidance is used for clinical context, symptoms, and the limitations of early-pregnancy diagnosis. The calculator performs table lookup only; it does not create a combined risk model, diagnose miscarriage, or replace prenatal care.