Note: These figures are based on general population statistics and do not account for individual medical history, genetic factors, or lifestyle. This tool is for educational purposes only and is not a substitute for professional medical advice.
function calculateMiscarriageStats() {
var weekInput = document.getElementById("gestationWeek");
var ageInput = document.getElementById("maternalAge");
var historyInput = document.getElementById("previousHistory");
var resultsArea = document.getElementById("results-area");
var successRateDisplay = document.getElementById("successRateDisplay");
var riskRateDisplay = document.getElementById("riskRateDisplay");
var successBar = document.getElementById("successBar");
// Parse inputs
var week = parseInt(weekInput.value);
var age = parseFloat(ageInput.value);
var historyCount = parseInt(historyInput.value);
if (isNaN(week) || isNaN(age)) {
alert("Please enter valid numbers for week and age.");
return;
}
// Base Risk Data (approximate aggregates from medical literature)
// Format: Week: Base Probability Percentage
var baseRisks = {
3: 30.0,
4: 24.0,
5: 21.0,
6: 14.0, // Significant drop often seen after heartbeat
7: 8.5,
8: 5.0,
9: 3.0,
10: 2.0,
11: 1.5,
12: 1.0,
13: 0.8,
14: 0.7,
15: 0.6,
16: 0.5,
17: 0.5,
18: 0.4,
19: 0.4,
20: 0.3
};
var currentRisk = baseRisks[week] || 0.5;
// Age Adjustment Factors
var ageMultiplier = 1.0;
if (age = 30 && age = 35 && age = 40 && age = 45) {
ageMultiplier = 5.0;
}
// History Adjustment Factors (slight increase for recurrent loss history)
var historyMultiplier = 1.0;
if (historyCount === 1) historyMultiplier = 1.2;
if (historyCount === 2) historyMultiplier = 1.4;
if (historyCount >= 3) historyMultiplier = 1.6;
// Calculate Final Risk
var adjustedRisk = currentRisk * ageMultiplier * historyMultiplier;
// Cap risk at realistic maximums (it rarely exceeds 50-60% even in high risk unless biochemical)
if (adjustedRisk > 70) adjustedRisk = 70;
// Ensure risk doesn't drop below a baseline minimum (0.1%)
if (adjustedRisk < 0.1) adjustedRisk = 0.1;
// Calculate Success Rate
var successRate = 100 – adjustedRisk;
// Display Results
successRateDisplay.innerHTML = successRate.toFixed(1) + "%";
riskRateDisplay.innerHTML = adjustedRisk.toFixed(1) + "%";
// Update Bar Width
successBar.style.width = successRate + "%";
// Show the results area
resultsArea.style.display = "block";
}
Understanding Miscarriage Rates by Week
Pregnancy is a journey filled with excitement and anxiety. One of the most common concerns for expectant parents is the risk of miscarriage. Statistical data shows that the risk of pregnancy loss drops significantly as the pregnancy progresses.
Our Miscarriage Rate Calculator by Week uses aggregated data from medical studies to provide an estimated probability of pregnancy continuation based on gestation week, maternal age, and previous history.
The "Danger Zone" vs. The Safety Zone
The majority of miscarriages occur within the first trimester (the first 12 weeks).
Weeks 3-5: This is the period of chemical pregnancies. The risk is highest here (20-30%) as implantation is still establishing.
Weeks 6-7: Once a heartbeat is detected via ultrasound, the risk of miscarriage often drops dramatically, often falling below 10%.
Weeks 8-12: As the placenta takes over hormone production and the fetus develops, the risk steadily declines to roughly 1-2% by the end of the first trimester.
Week 13+ (Second Trimester): The risk of loss in the second trimester is statistically very low, usually less than 1%.
Factors Influencing Pregnancy Loss Risk
While the week of gestation is the primary indicator of risk reduction, other factors play a crucial role in the statistical likelihood of miscarriage.
1. Maternal Age
Age is the most significant risk factor for miscarriage due to the decline in egg quality over time, which increases the chance of chromosomal abnormalities.
Under 35: The risk is generally aligned with the baseline average (roughly 10-15% overall risk for confirmed pregnancies).
Age 35-39: The risk increases moderately to approximately 20-25%.
Age 40-44: The risk rises significantly, often reaching 40-50%.
Age 45+: The risk is substantially higher, often exceeding 50%.
2. Previous History
While one previous miscarriage does not significantly increase the risk for the next pregnancy, recurrent pregnancy loss (3 or more consecutive losses) can indicate underlying issues that may elevate the statistical risk slightly.
How to Interpret the Results
This calculator provides a statistical estimate, not a diagnosis. A result showing a "95% Probability of Continuing Pregnancy" is very reassuring, but it is based on population averages.
Success Rate: This percentage represents the likelihood that the pregnancy will continue to the next week safely.
Miscarriage Risk: This represents the statistical probability of loss at this specific stage of gestation.
Frequently Asked Questions
Does hearing the heartbeat lower the risk?
Yes. Studies indicate that once a fetal heartbeat is detected (usually around week 6 or 7), the risk of miscarriage drops significantly, often to below 10%, provided there are no other complications (like bleeding).
Why is the risk higher in the first few weeks?
Many early losses (chemical pregnancies) occur due to chromosomal abnormalities that prevent the embryo from developing properly. This is nature's way of ending a pregnancy that would not be viable.
When can I feel "safe"?
While no pregnancy is 100% risk-free, most medical professionals agree that passing the 12-week mark (the end of the first trimester) is a major milestone where the risk of miscarriage becomes negligible for most women.