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Category Medicine & Tests

⚠️ Disclaimer: Results are estimates. Consult a doctor for medical advice.

BPD (mm)

HC (mm)

AC (mm)

FL (mm)

Estimated Fetal Weight (EFW)

0 g

0 lbs 0 oz

Composite Gestational Age

0w 0d

Based on average of parameters

Parameter	Est. Age	Percentile (Approx)

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About

Fetal biometry involves measuring specific anatomical parts of the fetus via ultrasound to assess growth and gestational age (GA). This calculator utilizes the Hadlock regression models, which are the standard in obstetrics for estimating the Estimated Fetal Weight (EFW). Accurate assessment is critical for identifying fetal growth restriction (FGR) or macrosomia (excessive growth).

The tool processes four standard biometric indices: Biparietal Diameter (BPD), Head Circumference (HC), Abdominal Circumference (AC), and Femur Length (FL). By comparing these inputs against a statistical database of standard deviations for each week of gestation, the tool provides a percentile ranking, indicating how the fetus compares to the population average.

Disclaimer: This tool is for educational and informational purposes only. It is not a medical device and should not replace professional clinical judgment or professional ultrasound reports.

Formulas

This tool uses the Hadlock IV formula for Estimated Fetal Weight (EFW). The formula is logarithmic:

log₁₀(EFW) = 1.3596 − 0.00386(AC)×FL + 0.0064(HC) + 0.00061(BPD)×AC + 0.0424(AC) + 0.174(FL)

All inputs are in millimeters (mm). The result is converted to grams. Percentiles are calculated using the Z-score method based on the gestational age:

Z = Value − MeanSD

Reference Data

Measurement	Full Name	Anatomical Target
BPD	Biparietal Diameter	Width of the head (ear-to-ear)
HC	Head Circumference	Perimeter of the skull
AC	Abdominal Circumference	Perimeter of the abdomen (liver level)
FL	Femur Length	Length of the thigh bone

Frequently Asked Questions

Frank Hadlock published several formulas in the 1980s that correlate fetal body measurements with weight. Hadlock IV is widely considered the most accurate as it uses four parameters (head, abdomen, and femur) to balance errors if one part is measured incorrectly or if the baby has an asymmetric shape.

The percentile tells you where the baby fits compared to 100 other babies of the same age. The 50th percentile is exactly average. Below the 10th percentile may indicate "Small for Gestational Age" (SGA), while above the 90th may indicate "Large for Gestational Age" (LGA).

Standard growth charts are derived from singleton (one baby) pregnancies. While often used for twins, the growth patterns for multiples can slow down in the third trimester compared to singletons.