👶 Estimated Fetal Weight (Hadlock)
The Hadlock four-parameter formula estimates fetal weight from BPD, HC, AC, and FL, the most widely used sonographic EFW method.
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)
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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.
Worked calculation
The values below come from this tool's own example placeholders and are computed server-side with the formula shown on this page, so the arithmetic can be checked quickly. It demonstrates how to substitute values only — it is not clinical advice and not a real case.
| Biparietal diameter BPD | 9.0 cm |
|---|---|
| Head circumference HC | 32.0 cm |
| Abdominal circumference AC | 30.0 cm |
| Femur length FL | 6.5 cm |
→Estimated fetal weight2396g
- ≈ ±15% interval：2036 ~ 2755 g
Frequently asked questions
- What is Estimated Fetal Weight (Hadlock)?
- The Hadlock four-parameter formula estimates fetal weight from BPD, HC, AC, and FL, the most widely used sonographic EFW method.
- How is Estimated Fetal Weight (Hadlock) calculated? What is the core formula?
- 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.
- When is Estimated Fetal Weight (Hadlock) used?
- 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.
- What are the key clinical points for Estimated Fetal Weight (Hadlock)?
- 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.
- What are the limits and cautions when using Estimated Fetal Weight (Hadlock)?
- For licensed clinicians and clinical researchers. Interpret results with history, investigations and local protocols; not a diagnosis or prescription, and not a substitute for multidisciplinary decision-making or local guidelines.
- How is Estimated Fetal Weight (Hadlock) calculated in practice? Can you show a worked example?
- Inputs: Biparietal diameter BPD 9.0 cm, Head circumference HC 32.0 cm, Abdominal circumference AC 30.0 cm, Femur length FL 6.5 cm → Result: Estimated fetal weight 2396 g（≈ ±15% interval: 2036 ~ 2755 g）