👶 Estimated Fetal Weight (Hadlock)

When to use

Enter the four biometric measurements in centimeters; the tool returns EFW with an approximate ±15% interval. Judge SGA/LGA against a gestational-age growth curve, not absolute grams.

How it works

log10(EFW) = 1.3596 + 0.0064·HC + 0.0424·AC + 0.174·FL + 0.00061·BPD·AC − 0.00386·AC·FL (all in cm); EFW = 10^log10. Reported interval ≈ EFW × 0.85 to × 1.15.

Key points

• About 85% of estimates fall within ±15% of true weight; error widens at the extremes of fetal size, with oligohydramnios, and at extreme gestational ages. (original synthesis · not guideline verbatim)
• A common pitfall is entering measurements in millimeters — the formula expects centimeters, and mm input grossly overestimates weight.
• EFW is a point estimate; growth-restriction or macrosomia decisions require GA-specific percentiles and serial measurements, not a single weight.

References

• Hadlock FP, et al. Estimation of fetal weight with the use of head, body, and femur measurements. Am J Obstet Gynecol. 1985;151(3):333-337.
• ISUOG Practice Guidelines: ultrasound assessment of fetal biometry and growth. Ultrasound Obstet Gynecol. 2019;53(6):715-723.

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