Miscarriage Probability Calculator

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Reviewed and conceptualized by: David Chen, MD (Obstetric Specialist)

This tool provides a conceptual estimation of miscarriage probability based on key clinical factors, primarily gestational age. Please note this is a conceptual model for educational purposes and should not replace professional medical advice.

Miscarriage Probability Calculator

Your Estimated Probability: —

Miscarriage Probability Calculator Formula

The estimation of miscarriage probability often relies on statistical models based on large population studies, factoring primarily gestational age (weeks) and maternal age. Our conceptual model uses a simplified two-step approach:

Step 1: Determine Base Risk based on Weeks of Gestation (WOG).

$$ \text{Base Risk} = f(\text{WOG}) $$

Step 2: Apply an Age Multiplier ($A_m$) based on Maternal Age (Age).

$$ \text{Probability} (P) = \text{Base Risk} \times A_m $$

Formula Sources:

Variables

A clear understanding of the input variables is essential for accurate risk estimation:

  • Weeks of Gestation (WOG): The most critical factor. The risk drops significantly for every week past 6 weeks. Enter the number of weeks since your last menstrual period.
  • Maternal Age (Years): A key risk multiplier. Probability increases after age 35 and again after age 40.
  • Number of Previous Miscarriages: History of loss increases the future risk. This is an additive factor in most clinical models.

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What is Miscarriage Probability Calculator?

The Miscarriage Probability Calculator is a tool designed to provide an individual risk assessment for a spontaneous pregnancy loss (miscarriage) based on data-driven estimates. It primarily calculates the risk of loss *after* a heartbeat has been detected, as this is the point where the risk drops sharply and becomes more reliably quantifiable by week.

The estimates provided are statistical averages. It’s crucial to understand that risk factors are often complex, involving genetics, uterine health, and environmental factors not captured by simple inputs. This tool should serve as a source of statistical context, not as a diagnostic tool. Consistent monitoring by a physician is the only way to track pregnancy progress.

How to Calculate Miscarriage Probability (Example)

Here is a step-by-step example using our conceptual framework:

  1. Gather Data: A user is 37 years old (Age), 8 weeks pregnant (WOG), and has had 1 previous miscarriage (PrevM).
  2. Determine Base Risk: At 8 WOG, the Base Risk is determined to be 9%.
  3. Determine Age Multiplier: At 37 years old (Age 35-39 bracket), the multiplier is 1.5.
  4. Apply Previous History Adjustment: An additional risk factor of 5% is added for 1 previous miscarriage.
  5. Calculate Final Probability: $P = (\text{Base Risk} \times \text{Age Multiplier}) + \text{Adjustment}$ $$ P = (9\% \times 1.5) + 5\% = 13.5\% + 5\% = 18.5\% $$
  6. Interpret Result: The estimated probability of miscarriage for this individual is 18.5%.

Frequently Asked Questions (FAQ)

Is the probability risk higher in the first trimester?

Yes, the vast majority of miscarriages occur in the first trimester (before 13 weeks). Once a pregnancy reaches the second trimester, the risk of loss drops to approximately 1-3%.

Does a history of previous miscarriages significantly increase the risk?

A history of one miscarriage only slightly increases the risk. However, the risk factor increases more substantially after two or three consecutive losses (known as recurrent pregnancy loss).

Can lifestyle changes affect the miscarriage probability?

While most losses are due to chromosomal abnormalities, maintaining a healthy weight, avoiding smoking, limiting caffeine and alcohol, and managing chronic conditions (like diabetes) can optimize the environment and potentially reduce non-chromosomal risks.

What is the maximum Weeks of Gestation I should enter?

Since this calculator focuses on the risk of miscarriage (defined as a loss before 20 weeks), the most relevant inputs are typically between 6 and 14 weeks, where the probability is most volatile.

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