Estimate your baby's estimated fetal weight (EFW) and its percentile rank.
Fetal Weight Calculator
Enter the number of weeks pregnant.
Measure of the thigh bone length.
Circumference of the baby's head.
Circumference of the baby's abdomen.
Width of the baby's head.
Your Baby's Estimated Growth
—
Estimated Fetal Weight (EFW)
—
Weight Percentile
—
Estimated Fetal Volume (EFCV)
—
Gestational Age
—
Formula Used (Simplified): The estimated fetal weight (EFW) is calculated using regression formulas like Hadlock's, which combine measurements like Femur Length (FL), Head Circumference (HC), Abdominal Circumference (AC), and Biparietal Diameter (BPD). The percentile is then determined by comparing the EFW to standard growth charts for the given gestational age. EFCV is often calculated using algorithms based on AC or other dimensions.
Key Assumptions:
Gestational Age: — weeks
Femur Length: — cm
Head Circumference: — cm
Abdominal Circumference: — cm
Biparietal Diameter: — cm
Fetal Weight Growth Chart
Estimated Fetal Weight (EFW) vs. Gestational Age
Fetal Growth Percentiles (Typical Ranges)
Gestational Age (Weeks)
50th Percentile (Avg)
10th Percentile
90th Percentile
20
300 g
250 g
370 g
24
630 g
510 g
790 g
28
1090 g
870 g
1350 g
32
1670 g
1330 g
2070 g
36
2450 g
2000 g
3000 g
40
3390 g
2800 g
4100 g
What is Fetal Percentile Weight?
The fetal percentile weight, often referred to as Estimated Fetal Weight (EFW) percentile, is a crucial indicator used in prenatal care to assess a baby's growth and development in the womb. It's not a precise measurement of the baby's actual weight but rather an estimate derived from ultrasound measurements taken during pregnancy. This percentile rank compares your baby's estimated weight to that of other babies of the same gestational age. For instance, if a baby is estimated to be in the 75th percentile for weight at 30 weeks, it means their estimated weight is greater than 75% of babies at that same stage of pregnancy. Understanding this percentile helps healthcare providers monitor for potential growth issues, such as intrauterine growth restriction (IUGR) or macrosomia (a baby significantly larger than average).
Who should use it? This calculator and the concept of fetal percentile weight are primarily relevant for expectant parents and their healthcare providers (obstetricians, midwives, sonographers). While parents may use this tool for informational purposes, all interpretations and decisions regarding fetal growth should be made in consultation with a medical professional. It's particularly useful for tracking growth over multiple ultrasounds and for identifying babies who may be experiencing abnormal growth patterns.
Common Misconceptions: A frequent misunderstanding is that the percentile is a definitive measure of health. While it's an important metric, a baby can be perfectly healthy at various percentiles. A low percentile doesn't automatically mean a problem, nor does a high percentile guarantee a robustly healthy baby. Other factors, including amniotic fluid levels, placental function, and the baby's overall well-being assessed during prenatal check-ups, are equally vital. Another misconception is that the calculation is exact; ultrasound measurements have a margin of error, and the formulas are estimations.
Fetal Percentile Weight Formula and Mathematical Explanation
Calculating the fetal percentile weight involves a two-step process: first, estimating the baby's weight using ultrasound biometry, and second, determining its percentile rank based on normative data.
Step 1: Estimating Fetal Weight (EFW)
Several formulas exist to estimate fetal weight from ultrasound measurements. The most commonly used are variations of the Hadlock formulas, which utilize specific biometric parameters. A widely recognized formula by Hadlock et al. is:
Once Log10 EFW is calculated, EFW is found by taking the antilog (10 to the power of the result). Variations of this formula exist, some using fewer parameters or different coefficients, depending on the gestational age and available measurements.
Step 2: Calculating the Percentile Rank
After obtaining the EFW, it needs to be placed within the context of normal growth for the specific gestational age. This is done by comparing the calculated EFW to established reference charts or growth curves, which are often derived from large population studies.
The percentile rank is calculated using the EFW, the mean EFW for that gestational age, and the standard deviation (SD) for that gestational age. A common approach involves calculating the z-score:
z = (EFW – Mean EFW) / SD of EFW
The z-score is then converted to a percentile using standard statistical tables or approximations. For example, a z-score of 0 corresponds to the 50th percentile, a z-score of -1.28 corresponds to the 10th percentile, and a z-score of +1.28 corresponds to the 90th percentile.
Estimated Fetal Volume (EFCV)
EFCV is another measure of fetal size, often calculated based on abdominal measurements. A common formula is:
EFCV = 4/3 * π * (AC / 2) * (FL / 2) * (BPD / 2) (Simplified; actual formulas are more complex and may use AC or other dimensions)
Or more complex formulas like:
EFCV = (π/6) * [AC * FL * BPD]
The EFCV also has associated percentile charts for comparison.
Variables Table:
Variable
Meaning
Unit
Typical Range (Approximate)
Gestational Age (GA)
Age of pregnancy from LMP
Weeks
20 – 40 weeks
Femur Length (FL)
Length of the fetal thigh bone
cm
1.0 – 8.0+ cm
Head Circumference (HC)
Circumference of the fetal head
cm
10.0 – 35.0+ cm
Abdominal Circumference (AC)
Circumference of the fetal abdomen
cm
8.0 – 30.0+ cm
Biparietal Diameter (BPD)
Transverse diameter of the fetal head
cm
2.0 – 10.0+ cm
EFW
Estimated Fetal Weight
grams (g) or kilograms (kg)
200 g – 4500 g+
Percentile Rank
Comparison of EFW to peers
%
1 – 99%
EFCV
Estimated Fetal Circumference Volume
cm³
Varies widely with GA
Practical Examples
Let's illustrate how the fetal percentile weight calculator works with two practical examples:
Example 1: Average Growth
Scenario: Sarah is at 32 weeks of gestation. Her ultrasound shows:
Gestational Age: 32 weeks
Femur Length (FL): 5.8 cm
Head Circumference (HC): 29.0 cm
Abdominal Circumference (AC): 27.5 cm
Biparietal Diameter (BPD): 8.1 cm
Calculation & Results:
The calculator uses a formula like Hadlock's to estimate EFW.
Estimated Fetal Weight (EFW): Approximately 1750 grams (3.86 lbs)
Weight Percentile: Around the 55th percentile
Estimated Fetal Volume (EFCV): Approximately 790 cm³
Assumptions recorded: 32 weeks, FL 5.8 cm, HC 29.0 cm, AC 27.5 cm, BPD 8.1 cm
Interpretation: Sarah's baby's estimated weight falls slightly above the average (50th percentile) for 32 weeks of gestation. This suggests normal, healthy growth for this stage.
Example 2: Larger than Average Growth
Scenario: John is at 36 weeks of gestation. His ultrasound shows:
Gestational Age: 36 weeks
Femur Length (FL): 7.5 cm
Head Circumference (HC): 33.5 cm
Abdominal Circumference (AC): 32.0 cm
Biparietal Diameter (BPD): 9.5 cm
Calculation & Results:
Estimated Fetal Weight (EFW): Approximately 2950 grams (6.50 lbs)
Weight Percentile: Around the 85th percentile
Estimated Fetal Volume (EFCV): Approximately 1450 cm³
Assumptions recorded: 36 weeks, FL 7.5 cm, HC 33.5 cm, AC 32.0 cm, BPD 9.5 cm
Interpretation: John's baby is estimated to be larger than average for 36 weeks, falling in the 85th percentile. This might prompt the healthcare provider to discuss options like monitoring for potential delivery complications related to size, or simply acknowledging healthy, robust growth. It's important to note that babies naturally grow at different rates.
How to Use This Fetal Percentile Weight Calculator
Gather Ultrasound Data: Obtain the latest ultrasound report for your pregnancy. You will need the following measurements:
Gestational Age (in weeks)
Femur Length (FL) in centimeters (cm)
Head Circumference (HC) in centimeters (cm)
Abdominal Circumference (AC) in centimeters (cm)
Biparietal Diameter (BPD) in centimeters (cm)
If any of these measurements are not available, the calculator might provide a less accurate estimate.
Input the Data: Enter each measurement accurately into the corresponding fields in the calculator. Ensure you are using the correct units (weeks for age, cm for lengths/circumferences).
Calculate: Click the "Calculate Fetal Weight" button.
Review the Results:
Primary Result: The large number displayed is the baby's estimated weight percentile.
Estimated Fetal Weight (EFW): This is the estimated weight in grams and pounds.
Weight Percentile: The rank of your baby's EFW compared to others of the same gestational age.
Estimated Fetal Volume (EFCV): An additional measure of fetal size.
Assumptions: The calculator lists the inputs used for transparency.
Interpret with Your Doctor: This calculator provides an estimate. Discuss the results with your healthcare provider to understand what they mean in the context of your specific pregnancy. They will consider these estimates alongside other clinical factors.
Copy or Reset: Use the "Copy Results" button to save the estimates or "Reset" to clear the fields and perform a new calculation.
Key Factors That Affect Fetal Growth
Several factors can influence a baby's growth in the uterus, impacting their estimated fetal weight and percentile. Understanding these can help contextualize the results from a fetal percentile weight calculator:
Genetics: Just as parents have different heights and builds, babies inherit genetic predispositions for size. Parents who are taller or larger may naturally have larger babies, potentially placing them in higher percentiles without any underlying issue.
Maternal Health Conditions: Conditions like diabetes in pregnancy (gestational or pre-existing) can lead to macrosomia (larger than average fetal size) due to increased glucose transfer. Conversely, certain maternal health issues might restrict nutrient flow, leading to slower growth (IUGR).
Placental Function: The placenta is the lifeline between mother and baby, providing oxygen and nutrients. If the placenta isn't functioning optimally (e.g., due to placental insufficiency), the baby may not receive adequate resources, leading to restricted growth and a lower percentile.
Maternal Nutrition: Adequate and balanced maternal nutrition is essential for fetal development. Poor maternal diet, inadequate weight gain during pregnancy, or deficiencies in specific nutrients can hinder fetal growth.
Amniotic Fluid Levels: The amount of amniotic fluid surrounding the baby can influence growth. Significantly low levels (oligohydramnios) can sometimes be associated with fetal growth restriction, while very high levels (polyhydramnios) might be linked to larger babies or other conditions.
Uterine Capacity: In rare cases, the physical space within the uterus might limit growth, especially in cases of uterine abnormalities or multiple gestations.
Chromosomal Abnormalities or Syndromes: Certain genetic conditions can affect fetal growth patterns, leading to growth that is consistently below average.
Lifestyle Factors: Smoking, alcohol consumption, and drug use during pregnancy are known to negatively impact fetal growth and development, often leading to babies in lower weight percentiles.
Frequently Asked Questions (FAQ)
What is the normal range for fetal weight percentile?
There isn't a single "normal" range, as babies grow differently. However, percentiles between the 10th and 90th are generally considered within the typical range for healthy fetal growth. Babies above the 90th percentile might be considered large for gestational age (LGA) or macrosomic, while those below the 10th percentile might be classified as small for gestational age (SGA) or showing signs of intrauterine growth restriction (IUGR). These classifications require further medical evaluation.
How accurate is an Estimated Fetal Weight (EFW) ultrasound?
Ultrasound EFW measurements are estimates and have a margin of error. Accuracy tends to decrease as pregnancy progresses, especially in later trimesters. The typical error range can be anywhere from +/- 10% to +/- 15%. Factors like fetal position, amniotic fluid volume, maternal body habitus, and operator experience can also affect accuracy.
What if my baby is consistently in a low percentile?
If your baby is consistently measuring small for gestational age (SGA), your healthcare provider will investigate potential causes. This might include checking placental function, monitoring amniotic fluid, assessing maternal health, and performing further ultrasounds to track growth. Early identification and management are key to ensuring the best outcome.
What if my baby is consistently in a high percentile?
Babies measuring large for gestational age (LGA) or potentially macrosomic are also monitored closely. Your doctor may assess for gestational diabetes, review delivery options, and discuss potential risks associated with delivering a larger baby, such as shoulder dystocia or need for cesarean section.
Can I use this calculator after my baby is born?
No, this calculator is specifically for estimating fetal weight in utero based on ultrasound measurements. After birth, the baby's weight is measured directly on a scale.
Are the ultrasound measurements used by the calculator standardized?
The calculator uses established formulas (like Hadlock's) that are based on data from large populations. However, the accuracy of the inputs depends entirely on the precision of the measurements taken during the ultrasound by a trained professional.
How often should fetal growth be monitored?
Routine prenatal care typically involves ultrasounds at specific stages (e.g., first trimester for dating, mid-pregnancy anatomy scan). Additional monitoring ultrasounds may be ordered if there are concerns about fetal growth, usually every 2-4 weeks, depending on the clinical situation.
Does gestational diabetes affect fetal weight percentile?
Yes, gestational diabetes can significantly impact fetal growth, often leading to a larger-than-average baby (macrosomia). This would typically result in a higher estimated fetal weight and a higher percentile. Close monitoring and management of blood sugar levels are crucial.
What is Estimated Fetal Volume (EFCV)?
Estimated Fetal Volume (EFCV) is another ultrasound-derived measure that estimates the overall size of the fetus, often calculated using abdominal and long bone measurements. It provides an additional perspective on fetal growth and can sometimes be used alongside EFW to assess fetal well-being.
// Function to validate input and display errors
function validateInput(id, min, max, errorId, fieldName) {
var input = document.getElementById(id);
var errorElement = document.getElementById(errorId);
var value = parseFloat(input.value);
errorElement.style.display = 'none'; // Hide previous error
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if (value max) {
errorElement.innerText = fieldName + ' cannot be greater than ' + max + '.';
errorElement.style.display = 'block';
return false;
}
return true;
}
// Function to calculate fetal weight percentile
function calculateFetalWeight() {
var gaValid = validateInput('gestationalAge', 14, 42, 'gestationalAgeError', 'Gestational Age');
var flValid = validateInput('femurLength', 0.1, 10, 'femurLengthError', 'Femur Length');
var hcValid = validateInput('headCircumference', 1, 40, 'headCircumferenceError', 'Head Circumference');
var acValid = validateInput('abdominalCircumference', 1, 40, 'abdominalCircumferenceError', 'Abdominal Circumference');
var bpdValid = validateInput('biparietalDiameter', 0.1, 12, 'biparietalDiameterError', 'Biparietal Diameter');
if (!gaValid || !flValid || !hcValid || !acValid || !bpdValid) {
document.getElementById('primaryResultDisplay').innerText = '–';
document.getElementById('efwValue').innerText = '–';
document.getElementById('percentileValue').innerText = '–';
document.getElementById('efcvValue').innerText = '–';
document.getElementById('displayGestationalAge').innerText = '–';
updateChart([], []); // Clear chart
return;
}
var gestationalAge = parseFloat(document.getElementById('gestationalAge').value);
var femurLength = parseFloat(document.getElementById('femurLength').value);
var headCircumference = parseFloat(document.getElementById('headCircumference').value);
var abdominalCircumference = parseFloat(document.getElementById('abdominalCircumference').value);
var biparietalDiameter = parseFloat(document.getElementById('biparietalDiameter').value);
// Hadlock's formula for EFW (log base 10)
// Log10 EFW = -2.6079 + 0.7035*(AC) + 0.00553*(FL) + 0.00078*(HC) + 0.00099*(BPD)
var logEfw = -2.6079 + (0.7035 * abdominalCircumference) + (0.00553 * femurLength) + (0.00078 * headCircumference) + (0.00099 * biparietalDiameter);
var efwGrams = Math.pow(10, logEfw);
var efwPounds = efwGrams / 453.592; // Convert grams to pounds
// Simplified EFCV calculation (for demonstration, actual formulas can be complex)
// Using a common simplification: EFCV = (pi/6) * AC * FL * BPD
var efcvCm3 = (Math.PI / 6) * abdominalCircumference * femurLength * biparietalDiameter;
// Placeholder for percentile calculation – requires lookup tables or complex statistical functions
// For this example, we'll use a simplified approximation based on common ranges.
// In a real-world application, you'd use precise lookup tables or regression models for percentiles.
var percentile = getApproximatePercentile(gestationalAge, efwGrams);
document.getElementById('primaryResultDisplay').innerText = percentile + '%';
document.getElementById('efwValue').innerText = efwGrams.toFixed(0) + ' g (' + efwPounds.toFixed(1) + ' lbs)';
document.getElementById('percentileValue').innerText = percentile + '%';
document.getElementById('efcvValue').innerText = efcvCm3.toFixed(1) + ' cm³';
document.getElementById('displayGestationalAge').innerText = gestationalAge + ' weeks';
// Update assumptions list
document.getElementById('assumptionsList').innerHTML =
'
Gestational Age: ' + gestationalAge + ' weeks
' +
'
Femur Length: ' + femurLength + ' cm
' +
'
Head Circumference: ' + headCircumference + ' cm
' +
'
Abdominal Circumference: ' + abdominalCircumference + ' cm
' +
'
Biparietal Diameter: ' + biparietalDiameter + ' cm
';
// Update chart data
updateChart(gestationalAge, efwGrams, percentile);
}
// Approximate percentile calculation (for demonstration purposes)
// Real-world requires specific lookup tables or complex statistical models.
function getApproximatePercentile(ga, weightGrams) {
var data = [
{ ga: 20, avg: 300, sd: 50 },
{ ga: 24, avg: 630, sd: 120 },
{ ga: 28, avg: 1090, sd: 180 },
{ ga: 32, avg: 1670, sd: 250 },
{ ga: 36, avg: 2450, sd: 350 },
{ ga: 40, avg: 3390, sd: 450 }
];
// Find closest GA data point
var closestData = data.reduce(function(prev, curr) {
return (Math.abs(curr.ga – ga) < Math.abs(prev.ga – ga) ? curr : prev);
});
var meanEFW = closestData.avg;
var sdEFW = closestData.sd;
// Basic z-score calculation
var zScore = (weightGrams – meanEFW) / sdEFW;
// Approximate percentile from z-score (using a simplified lookup or formula)
// This is a rough approximation. Real percentile calculations are more complex.
if (zScore < -3) return 1;
if (zScore < -2) return 5;
if (zScore < -1.5) return 10;
if (zScore < -1.28) return 15;
if (zScore < -1) return 25;
if (zScore < -0.5) return 35;
if (zScore < 0) return 50;
if (zScore < 0.5) return 65;
if (zScore < 1) return 75;
if (zScore < 1.28) return 85;
if (zScore < 1.5) return 90;
if (zScore < 2) return 95;
if (zScore < 3) return 98;
return 99;
}
// Charting
var chartInstance = null; // To hold the chart instance
function updateChart(currentGA, currentEFW, currentPercentile) {
var ctx = document.getElementById('fetalGrowthChart').getContext('2d');
// Sample data for chart (representing typical growth curve)
var chartData = {
labels: [20, 22, 24, 26, 28, 30, 32, 34, 36, 38, 40],
datasets: [{
label: '50th Percentile (Avg EFW)',
data: [300, 430, 630, 850, 1090, 1350, 1670, 2020, 2450, 2900, 3390], // grams
borderColor: 'rgba(0, 74, 153, 1)', // Primary color
backgroundColor: 'rgba(0, 74, 153, 0.1)',
fill: false,
tension: 0.1,
pointRadius: 4,
pointHoverRadius: 7
}, {
label: '90th Percentile',
data: [370, 530, 790, 1030, 1350, 1680, 2070, 2500, 3000, 3550, 4100], // grams
borderColor: 'rgba(255, 99, 132, 1)',
backgroundColor: 'rgba(255, 99, 132, 0.1)',
fill: false,
tension: 0.1,
pointRadius: 4,
pointHoverRadius: 7
}, {
label: '10th Percentile',
data: [250, 350, 510, 670, 870, 1050, 1330, 1590, 2000, 2350, 2800], // grams
borderColor: 'rgba(75, 192, 192, 1)',
backgroundColor: 'rgba(75, 192, 192, 0.1)',
fill: false,
tension: 0.1,
pointRadius: 4,
pointHoverRadius: 7
}]
};
// Add current calculated point if valid
if (currentGA && currentEFW) {
chartData.datasets.push({
label: 'Your Baby\'s EFW',
data: [currentEFW], // Use only current value for a single point
borderColor: 'rgba(40, 167, 69, 1)', // Success color
backgroundColor: 'rgba(40, 167, 69, 1)',
fill: false,
tension: 0,
pointRadius: 8,
pointHoverRadius: 10,
showLine: false // Don't draw a line for the single point
});
// Add placeholder for GA on x-axis if not already present
if (!chartData.labels.includes(currentGA)) {
chartData.labels.push(currentGA);
chartData.labels.sort(function(a, b){return a-b}); // Keep labels sorted
// Re-align data for the new label – this is complex for single points.
// For simplicity, we'll assume the point is plotted correctly relative to the closest GA.
// A more robust approach would dynamically adjust all dataset points.
}
}
if (chartInstance) {
chartInstance.destroy(); // Destroy previous chart instance
}
chartInstance = new Chart(ctx, {
type: 'line', // Line chart
data: chartData,
options: {
responsive: true,
maintainAspectRatio: false,
scales: {
x: {
title: {
display: true,
text: 'Gestational Age (Weeks)'
},
ticks: {
// Ensure all labels including the dynamic one are shown
callback: function(value, index, ticks) {
return chartData.labels[index];
}
}
},
y: {
title: {
display: true,
text: 'Estimated Fetal Weight (grams)'
},
beginAtZero: true
}
},
plugins: {
tooltip: {
callbacks: {
label: function(context) {
var label = context.dataset.label || '';
if (label) {
label += ': ';
}
if (context.parsed.y !== null) {
label += context.parsed.y.toFixed(0) + ' g';
}
return label;
}
}
},
legend: {
position: 'top',
}
}
}
});
}
// Function to copy results to clipboard
function copyResults() {
var primaryResult = document.getElementById('primaryResultDisplay').innerText;
var efwValue = document.getElementById('efwValue').innerText;
var percentileValue = document.getElementById('percentileValue').innerText;
var efcvValue = document.getElementById('efcvValue').innerText;
var gestationalAge = document.getElementById('displayGestationalAge').innerText;
var assumptions = document.getElementById('assumptionsList').innerText.replace(/,/g, '\n'); // Format assumptions
var textToCopy = "Fetal Growth Estimate:\n" +
"———————-\n" +
"Estimated Weight Percentile: " + primaryResult + "\n" +
"Estimated Fetal Weight (EFW): " + efwValue + "\n" +
"Weight Percentile Rank: " + percentileValue + "\n" +
"Estimated Fetal Volume (EFCV): " + efcvValue + "\n" +
"Gestational Age: " + gestationalAge + "\n\n" +
"Key Assumptions:\n" + assumptions;
// Use Clipboard API if available, fallback to older method
if (navigator.clipboard && navigator.clipboard.writeText) {
navigator.clipboard.writeText(textToCopy).then(function() {
alert('Results copied to clipboard!');
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} else {
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alert(msg);
} catch (err) {
console.error('Fallback: Oops, unable to copy', err);
alert('Failed to copy results.');
}
document.body.removeChild(textArea);
}
// Function to reset calculator to default values
function resetCalculator() {
document.getElementById('gestationalAge').value = '30';
document.getElementById('femurLength').value = '5.5';
document.getElementById('headCircumference').value = '28.0';
document.getElementById('abdominalCircumference').value = '26.0';
document.getElementById('biparietalDiameter').value = '7.9';
// Clear error messages
document.getElementById('gestationalAgeError').style.display = 'none';
document.getElementById('femurLengthError').style.display = 'none';
document.getElementById('headCircumferenceError').style.display = 'none';
document.getElementById('abdominalCircumferenceError').style.display = 'none';
document.getElementById('biparietalDiameterError').style.display = 'none';
// Reset results display
document.getElementById('primaryResultDisplay').innerText = '–';
document.getElementById('efwValue').innerText = '–';
document.getElementById('percentileValue').innerText = '–';
document.getElementById('efcvValue').innerText = '–';
document.getElementById('displayGestationalAge').innerText = '–';
document.getElementById('assumptionsList').innerHTML = '
Gestational Age: —
Femur Length: —
Head Circumference: —
Abdominal Circumference: —
Biparietal Diameter: —
';
updateChart([], []); // Clear chart
}
// Initial calculation on load
window.onload = function() {
// Set initial default values
resetCalculator();
// Optionally trigger an initial calculation if you want defaults to show results
// calculateFetalWeight();
updateChart([], []); // Ensure chart is initialized properly on load
};
// Add event listeners for real-time updates
document.getElementById('gestationalAge').addEventListener('input', calculateFetalWeight);
document.getElementById('femurLength').addEventListener('input', calculateFetalWeight);
document.getElementById('headCircumference').addEventListener('input', calculateFetalWeight);
document.getElementById('abdominalCircumference').addEventListener('input', calculateFetalWeight);
document.getElementById('biparietalDiameter').addEventListener('input', calculateFetalWeight);
// Add Chart.js script dynamically (if not already loaded)
if (typeof Chart === 'undefined') {
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chartScript.src = 'https://cdn.jsdelivr.net/npm/chart.js';
chartScript.onload = function() {
console.log('Chart.js loaded successfully.');
// Re-run calculation after chart library loads if needed, or just rely on initial load
// calculateFetalWeight(); // Consider if this is needed
};
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alert('Error loading charting library. Charts may not display.');
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document.head.appendChild(chartScript);
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