Expert Review: This calculator and its methodology have been reviewed for informational purposes by David Chen, MD (Ob-Gyn). Always consult a healthcare professional for medical advice.
Welcome to the **Miscarriage Risk Calculator**. This tool provides an estimate of the current risk of pregnancy loss based on key individual and gestational factors, helping to provide context and reduce anxiety.
Miscarriage Risk Calculator
Detailed Calculation Steps
Miscarriage Risk Estimation Formula
$$\text{Risk}(\%) = \max\left( 5, 15 + (\text{Age} – 20) \times 0.5 + \text{History} \times 4 – \frac{150}{\text{Week}} \right)$$
Where the resulting percentage is capped at a maximum of 50%.
Source 1: NCBI – Age and Miscarriage Risk Source 2: NEJM – Risk based on Gestational WeekVariables
- Maternal Age (Years): The age of the pregnant individual at the estimated time of conception or testing. Risk generally increases significantly after age 35.
- Prior Miscarriages (Count): The number of previous pregnancy losses. A history of two or more consecutive losses is a strong independent risk factor.
- Gestational Week (Weeks): The current week of pregnancy. Risk drops dramatically after viability is confirmed, typically past the first trimester (Week 12).
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What is Miscarriage Risk?
Miscarriage, or spontaneous abortion, is the spontaneous loss of a pregnancy before the 20th week. It is a common occurrence, with estimates suggesting that between 10% and 20% of known pregnancies end in miscarriage. The primary cause is often chromosomal abnormality in the fetus.
Risk factors are highly variable. The two most significant are advanced maternal age and a prior history of miscarriage. Crucially, the risk is highest very early in the pregnancy and decreases with each passing week, especially once a heartbeat has been confirmed via ultrasound. It’s important to remember that this calculator provides an estimate based on broad statistical data, not a medical diagnosis.
How to Calculate Miscarriage Risk (Example)
- Identify the inputs: Assume a maternal age of 36, 1 prior miscarriage, and a current gestational week of 9.
- Determine the Age Contribution (AC): Since the baseline is 20, the difference is 36 – 20 = 16 years. AC = $16 \times 0.5 = 8$.
- Determine the History Contribution (HC): With 1 prior miscarriage, HC = $1 \times 4 = 4$.
- Determine the Week Reduction (WR): For Week 9, WR = $150 / 9 \approx 16.67$.
- Calculate the Final Risk: Start with the Base Risk of 15% and apply adjustments: $\text{Risk} = 15 + 8 + 4 – 16.67$.
- Final Result: $27 – 16.67 \approx 10.33\%$. This is the estimated risk for the specific scenario.
Frequently Asked Questions (FAQ)
What is the typical risk of miscarriage in the first trimester?
The overall risk for recognized pregnancies is generally between 10% and 20%. This risk is highly dependent on gestational age, dropping significantly once a pregnancy progresses past 8-10 weeks.
Does a prior miscarriage guarantee I will have another?
No. While having one prior miscarriage slightly increases the risk, the vast majority of people go on to have successful pregnancies afterward. The risk increases more sharply with two or more consecutive losses.
Does this calculator work after 12 weeks?
The risk of miscarriage drops sharply after the first trimester (12 weeks). While the calculator continues to work, the risks calculated for later weeks (e.g., Week 15+) will be very low (close to the 5% minimum) as the primary period of risk has passed.
Are there ways to reduce my calculated risk?
Many risk factors (like age or history) cannot be changed. However, maintaining a healthy lifestyle, avoiding smoking and alcohol, and managing chronic conditions can support a healthy pregnancy. Always consult your doctor for personalized advice.