Calculate the estimated fetal weight gain velocity between two ultrasound scans.
First Ultrasound Scan
Second Ultrasound Scan
Time Interval:0 days
Total Weight Gain:0 g
Growth Rate (Velocity):0 g/day
Weekly Growth Rate:0 g/week
Understanding Fetal Growth Velocity
Monitoring the rate at which a fetus grows is a critical component of prenatal care. While estimated fetal weight (EFW) at a single point in time tells us the size, the Fetal Growth Rate (or velocity) tells us how fast the baby is developing between two points in time. This calculator helps determine the daily and weekly weight gain based on two separate ultrasound measurements.
Note on Units: This calculator uses grams (g) for precision. If your ultrasound report lists weight in pounds and ounces, convert it to grams first (1 lb ≈ 453.6g, 1 oz ≈ 28.35g).
Why Measure Growth Rate?
Assessing growth velocity helps clinicians distinguish between a constitutionally small baby (one who is healthy but naturally small) and a baby suffering from Intrauterine Growth Restriction (IUGR). Conversely, it helps identify accelerated growth patterns that might suggest macrosomia, often associated with gestational diabetes.
Normal Fetal Growth Patterns
Fetal weight gain is not linear throughout pregnancy. It accelerates significantly in the third trimester.
20-28 Weeks: The fetus typically gains about 10-15 grams per day.
28-36 Weeks: Growth velocity often peaks, ranging from 25 to 35 grams per day.
36+ Weeks: The rate may slow down slightly as the placenta matures and space becomes limited, typically averaging 20-30 grams per day.
How to Interpret the Results
The output of this calculator provides the Average Daily Weight Gain (g/day). Here is a general guide to interpretation:
Below 10g/day (3rd Trimester): This may indicate slow growth. A doctor will typically correlate this with amniotic fluid levels and Doppler flow studies to assess placental function.
20g – 30g/day: This is generally considered the average healthy range for the third trimester.
Above 40g/day: This suggests accelerated growth. While often normal for larger parents, it can also be a marker for maternal glucose intolerance.
Factors Affecting Fetal Growth
Several variables can influence the numbers you see on an ultrasound report:
Maternal Health: Conditions like hypertension can restrict blood flow to the placenta, slowing growth.
Placental Function: The placenta's ability to transfer nutrients is the primary driver of weight gain.
Genetics: The height and weight of the parents play a significant role.
Multiple Gestation: Twins or triplets often have slower individual growth rates compared to singletons.
Disclaimer
This tool is for educational purposes only and is not a substitute for professional medical advice. Ultrasound weight estimates have a margin of error of +/- 15%. Always consult your obstetrician or maternal-fetal medicine specialist for interpretation of growth scans.
function calculateGrowth() {
// Get input elements
var date1Input = document.getElementById('date1');
var weight1Input = document.getElementById('weight1');
var date2Input = document.getElementById('date2');
var weight2Input = document.getElementById('weight2');
var resultArea = document.getElementById('result-area');
var errorDisplay = document.getElementById('error-display');
// Reset displays
resultArea.style.display = 'none';
errorDisplay.style.display = 'none';
errorDisplay.innerText = ";
// Get values
var d1 = new Date(date1Input.value);
var w1 = parseFloat(weight1Input.value);
var d2 = new Date(date2Input.value);
var w2 = parseFloat(weight2Input.value);
// Validation
if (!date1Input.value || !date2Input.value) {
errorDisplay.innerText = "Please select dates for both scans.";
errorDisplay.style.display = 'block';
return;
}
if (isNaN(w1) || isNaN(w2)) {
errorDisplay.innerText = "Please enter valid weights in grams for both scans.";
errorDisplay.style.display = 'block';
return;
}
if (d1 >= d2) {
errorDisplay.innerText = "The second scan date must be after the first scan date.";
errorDisplay.style.display = 'block';
return;
}
if (w1 <= 0 || w2 <= 0) {
errorDisplay.innerText = "Weights must be positive numbers.";
errorDisplay.style.display = 'block';
return;
}
// Calculations
// Time difference
var timeDiff = d2.getTime() – d1.getTime();
var daysDiff = timeDiff / (1000 * 3600 * 24); // Convert ms to days
// Ensure accurate rounding for days (handles potential daylight savings small offsets)
daysDiff = Math.round(daysDiff);
if (daysDiff === 0) {
errorDisplay.innerText = "Scans cannot be on the same day for a rate calculation.";
errorDisplay.style.display = 'block';
return;
}
// Weight difference
var weightDiff = w2 – w1;
// Daily rate
var dailyRate = weightDiff / daysDiff;
// Weekly rate
var weeklyRate = dailyRate * 7;
// Display Results
document.getElementById('res-days').innerText = daysDiff + " days";
document.getElementById('res-gain').innerText = weightDiff.toFixed(0) + " g";
document.getElementById('res-velocity').innerText = dailyRate.toFixed(1) + " g/day";
document.getElementById('res-weekly').innerText = weeklyRate.toFixed(1) + " g/week";
resultArea.style.display = 'block';
}