Professional Estimated Fetal Weight Calculation using Hadlock Formula
Fetal Biometry Input
Select current gestational age (20-42 weeks).
0 Days
1 Day
2 Days
3 Days
4 Days
5 Days
6 Days
Enter BPD in millimeters (mm).
Please enter a valid BPD (10-120mm).
Enter HC in millimeters (mm).
Please enter a valid HC (50-400mm).
Enter AC in millimeters (mm).
Please enter a valid AC (50-450mm).
Enter FL in millimeters (mm).
Please enter a valid FL (10-100mm).
Estimated Fetal Weight (EFW)
1850 g
Weight in Lbs/Oz4 lbs 1 oz
Estimated Percentile50th
Gestational Age Used31 Weeks 0 Days
Calculation based on Hadlock IV formula (Log10).
Biometry Summary
Measurement
Value (mm)
Value (cm)
Fetal Growth Chart
Blue Line: 50th Percentile (Average) | Red Dot: Your Estimated Weight
Understanding the EFW Fetal Weight Calculator
Monitoring fetal growth is a cornerstone of prenatal care. The efw fetal weight calculator is a critical tool used by sonographers and obstetricians to estimate the weight of a fetus based on ultrasound measurements. By inputting specific biometric data, this calculator provides an estimated fetal weight (EFW) that helps clinicians assess whether a baby is growing at a healthy rate.
Whether you are a healthcare professional verifying a scan or an expectant parent interpreting a report, understanding how the efw fetal weight calculator works is essential for tracking pregnancy progress.
What is the EFW Fetal Weight Calculator?
The efw fetal weight calculator is a mathematical model that combines various fetal body measurements to predict the total mass of the fetus. Since the baby cannot be weighed directly while in the womb, medical professionals rely on 2D ultrasound measurements of the head, abdomen, and femur bones to construct a 3D volume estimation.
This tool is primarily used to detect:
Macrosomia: A fetus that is significantly larger than average (often >90th percentile).
Intrauterine Growth Restriction (IUGR): A fetus that is not reaching its growth potential (often <10th percentile).
Appropriate for Gestational Age (AGA): Normal growth patterns between the 10th and 90th percentiles.
EFW Formula and Mathematical Explanation
The most widely accepted method for calculating EFW is the Hadlock formula. While there are several variations, the "Hadlock IV" formula is considered one of the most accurate because it utilizes four distinct biometric parameters.
The Variables
Variable
Full Name
Unit
Description
BPD
Biparietal Diameter
cm
The diameter of the head measured from ear to ear.
HC
Head Circumference
cm
The measurement around the fetal head.
AC
Abdominal Circumference
cm
The measurement around the fetal belly (most sensitive to weight).
FL
Femur Length
cm
The length of the thigh bone.
The Hadlock IV Equation
The mathematical derivation for the estimated weight (in grams) is logarithmic. The formula used in this efw fetal weight calculator is:
Note: All inputs in the formula above must be in centimeters (cm). Our calculator automatically converts your millimeter (mm) inputs to centimeters for accuracy.
Practical Examples
Example 1: 32 Weeks Gestation
A patient presents at 32 weeks. The ultrasound measurements are:
BPD: 81 mm (8.1 cm)
HC: 295 mm (29.5 cm)
AC: 280 mm (28.0 cm)
FL: 62 mm (6.2 cm)
Result: The calculator estimates a weight of approximately 1,950 grams (4 lbs 5 oz). This places the fetus near the 50th percentile, indicating average, healthy growth.
Example 2: Suspected Macrosomia
At 38 weeks, a scan reveals:
BPD: 96 mm
HC: 340 mm
AC: 360 mm (Larger than average)
FL: 74 mm
Result: The efw fetal weight calculator yields roughly 3,800 grams (8 lbs 6 oz). The large Abdominal Circumference (AC) significantly drives up the weight estimate, suggesting the baby is large for gestational age.
How to Use This EFW Fetal Weight Calculator
Select Gestational Age: Choose the number of weeks and days of the pregnancy. This is crucial for calculating the percentile.
Input Measurements: Enter the BPD, HC, AC, and FL values from your ultrasound report. Ensure you enter them in millimeters (mm), which is the standard unit on most medical reports.
Review Results: The calculator updates instantly. Look at the estimated weight in grams and the percentile ranking.
Analyze the Chart: The dynamic chart below the results plots your baby's weight against the average growth curve to visualize their progress.
Key Factors That Affect EFW Results
While the efw fetal weight calculator is a powerful tool, several factors can influence the accuracy of the estimation:
Fetal Position: If the baby is in a difficult position (e.g., head very low in the pelvis), obtaining accurate head measurements (BPD/HC) becomes challenging, potentially skewing the result.
Amniotic Fluid Levels: Low fluid (oligohydramnios) can make structures harder to visualize, while high fluid (polyhydramnios) allows the fetus to move more, making it harder to capture a still image.
Maternal Obesity: Increased maternal tissue can attenuate ultrasound waves, reducing image clarity and measurement precision.
Abdominal Shape: The AC is the most heavily weighted parameter for weight. If the fetal abdomen is compressed or slightly distorted during the scan, the weight error can be significant (up to ±15%).
Operator Experience: Ultrasound is operator-dependent. Slight variations in where the calipers are placed by the sonographer can change the inputs by millimeters, affecting the final gram count.
Genetic Potential: The calculator compares the fetus to a "standard" population. Parents who are naturally smaller or larger may have a healthy baby that simply plots on a lower or higher percentile curve.
Frequently Asked Questions (FAQ)
1. How accurate is the efw fetal weight calculator?
Generally, ultrasound weight estimates are accurate to within ±10-15% of the actual birth weight. The accuracy decreases as the pregnancy progresses towards full term.
2. What is a normal percentile?
Any percentile between the 10th and 90th is considered normal (Appropriate for Gestational Age). Below the 10th may indicate growth restriction, while above the 90th may indicate macrosomia.
3. Why is Abdominal Circumference (AC) so important?
The AC reflects the size of the fetal liver and subcutaneous fat stores. It is the only measurement that shrinks if the baby is malnourished, making it the best indicator of fetal nutritional status.
4. Can I use this calculator for twins?
Yes, but twins often have different growth curves than singletons, especially in the third trimester. Consult a specific twin growth chart for interpretation.
5. What if my result is "NaN"?
This usually means one of the inputs is missing or invalid. Ensure all fields (BPD, HC, AC, FL) contain positive numbers within realistic ranges.
6. Does the gender of the baby affect the weight?
Male fetuses are typically slightly heavier than female fetuses at the same gestational age, but standard EFW formulas like Hadlock do not usually adjust for gender.
7. How often should EFW be measured?
Growth scans are typically performed no less than 2-3 weeks apart. It takes time for significant growth to occur, and measuring too frequently can lead to false assumptions about growth velocity.
8. Is a high estimated weight dangerous?
Not necessarily. A high EFW may simply mean a large baby. However, it can be associated with gestational diabetes or increase the risk of shoulder dystocia during delivery, which is why doctors monitor it closely.