Chance of Miscarriage Calculator

Reviewed by David Chen, MD, MPH, a specialist in Women’s Health and Biostatistics, ensuring accuracy and clinical relevance.

Use this tool to estimate the probabilistic chance of miscarriage based on key factors like gestational age, maternal age, and prior pregnancy history.

Chance of Miscarriage Calculator

Detailed Risk Analysis

Enter your data and click ‘Calculate Risk’ to see the detailed breakdown.

Chance of Miscarriage Calculator Formula

$$ \text{Risk}(\%) = \text{Base Risk}(\text{Week}, \text{Age}) + (\text{Prior Miscarriages} \times \text{Factor}) $$ *Note: This calculation uses a simplified statistical model based on large cohort studies for illustrative purposes. Formula Source 1 | Source 2 (ACOG)

Variables

The calculation is based on the following key inputs:

• Maternal Age (Years): A primary factor, as risk increases significantly with age, particularly after 35.
• Gestational Week (Weeks): The most crucial variable. Risk is highest around Week 5 and drops sharply after Week 8. The calculator focuses on Weeks 5-12.
• Number of Previous Miscarriages: History of prior losses is a known risk multiplier, increasing the probability of a future event.

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What is Chance of Miscarriage Calculator?

The Chance of Miscarriage Calculator is a tool designed to provide an estimated probability of early pregnancy loss (defined as a non-induced embryonic or fetal death before 20 weeks of gestation). It takes into account well-established risk factors that modify an individual’s baseline probability, such as age and gestational week.

It is important to understand that this tool provides a statistical estimate, not a diagnosis. The risk of miscarriage changes daily; the greatest period of risk occurs before 8 weeks, decreasing substantially once a fetal heartbeat is detected and as the pregnancy progresses into the second trimester.

How to Calculate Chance of Miscarriage (Example)

Here is an illustrative step-by-step example of how the risk is estimated:

1. Determine Baseline Risk by Week: A 30-year-old woman at 7 weeks has a statistical baseline risk of, for example, 8%.
2. Adjust for Age Factor: Since she is 30 (within the average risk bracket), the age factor adjustment is 0%. Total risk remains 8%.
3. Adjust for Prior History: If she had one previous miscarriage, a risk factor of +3% is added.
4. Final Estimate: The total estimated risk is 8% (Baseline) + 0% (Age) + 3% (Prior History) = 11%.
5. Interpretation: This means for every 100 pregnancies with identical characteristics, 11 statistically result in miscarriage.

Frequently Asked Questions (FAQ)

Is the miscarriage risk calculator accurate?
It is statistically derived and clinically relevant, but it cannot account for all unique medical conditions or genetic factors. It should only be used for informational purposes and not as a substitute for professional medical advice.

How does age affect the probability of miscarriage?
Maternal age is one of the strongest predictors. For women over 40, the risk can be significantly higher than for women in their twenties, primarily due to increased prevalence of chromosomal abnormalities.

Does seeing a heartbeat guarantee a successful pregnancy?
Detection of a fetal heartbeat is highly reassuring. After detecting a heartbeat at 8 weeks, the risk drops dramatically to less than 5%, though some risk remains until the end of the first trimester.

What is the typical timeframe the risk covers?
The calculator provides the risk of having a miscarriage *from the current gestational day forward*. The greatest overall risk is typically concentrated in the first trimester (up to 12 weeks).