📏 Fetal Biometry–Gestational Age (Hadlock)
Derives the gestational age implied by each fetal biometric parameter and a composite ultrasound GA (Hadlock 1984), with an estimated fetal weight, to flag growth deviation against clinical dating.
An AC-implied GA lagging the head/femur by ≥ 2 weeks suggests asymmetric (placental) growth restriction; exceeding it by ≥ 2 weeks suggests macrosomia — both are flagged. (original synthesis · not guideline verbatim)
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When to use
Enter BPD/HC/AC/FL in millimeters (and optional clinical GA); the tool converts to cm internally and reports per-parameter GA, composite GA, EFW, and any asymmetry or dating discrepancy.
How it works
Per-parameter GA from Hadlock 1984 quadratics/cubics (e.g. AC-GA = 8.14 + 0.753·AC + 0.0036·AC²). Composite GA prefers the 4-parameter formula 10.85 + 0.060·HC·FL + 0.67·BPD + 0.168·AC. EFW by the available-parameter Hadlock regression.
Key points
- An AC-implied GA lagging the head/femur by ≥ 2 weeks suggests asymmetric (placental) growth restriction; exceeding it by ≥ 2 weeks suggests macrosomia — both are flagged. (original synthesis · not guideline verbatim)
- An established GA from first-trimester CRL or reliable LMP is not redated by third-trimester biometry; later measurements assess growth, not dates.
- Composite GA is most accurate in the second trimester; third-trimester biometric dating carries a wider error (often ±2–3 weeks).
References
- Hadlock FP, et al. Estimating fetal age: computer-assisted analysis of multiple fetal growth parameters. Radiology. 1984;152(2):497-501.
- ACOG/AIUM/SMFM. Methods for Estimating the Due Date. Committee Opinion 700. Obstet Gynecol. 2017;129(5):e150-e154.
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 | 80 mm |
|---|---|
| Head circumference HC | 290 mm |
| Abdominal circumference AC | 260 mm |
| Femur length FL | 55 mm |
| Clinical GA (optional, by LMP / first-trimester CRL) | 28 wk |
→Composite US gestational age30w1d(BPD+HC+AC+FL)
- Estimated fetal weight EFW：1512 g (±~15%, Hadlock4 four-param)
- BPD implied GA：32w1d
- HC implied GA：32w0d
Frequently asked questions
- What is Fetal Biometry–Gestational Age (Hadlock)?
- Derives the gestational age implied by each fetal biometric parameter and a composite ultrasound GA (Hadlock 1984), with an estimated fetal weight, to flag growth deviation against clinical dating.
- How is Fetal Biometry–Gestational Age (Hadlock) calculated? What is the core formula?
- Per-parameter GA from Hadlock 1984 quadratics/cubics (e.g. AC-GA = 8.14 + 0.753·AC + 0.0036·AC²). Composite GA prefers the 4-parameter formula 10.85 + 0.060·HC·FL + 0.67·BPD + 0.168·AC. EFW by the available-parameter Hadlock regression.
- When is Fetal Biometry–Gestational Age (Hadlock) used?
- Enter BPD/HC/AC/FL in millimeters (and optional clinical GA); the tool converts to cm internally and reports per-parameter GA, composite GA, EFW, and any asymmetry or dating discrepancy.
- What are the key clinical points for Fetal Biometry–Gestational Age (Hadlock)?
- An AC-implied GA lagging the head/femur by ≥ 2 weeks suggests asymmetric (placental) growth restriction; exceeding it by ≥ 2 weeks suggests macrosomia — both are flagged. (original synthesis · not guideline verbatim) An established GA from first-trimester CRL or reliable LMP is not redated by third-trimester biometry; later measurements assess growth, not dates. Composite GA is most accurate in the second trimester; third-trimester biometric dating carries a wider error (often ±2–3 weeks).
- What are the limits and cautions when using Fetal Biometry–Gestational Age (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 Fetal Biometry–Gestational Age (Hadlock) calculated in practice? Can you show a worked example?
- Inputs: Biparietal diameter BPD 80 mm, Head circumference HC 290 mm, Abdominal circumference AC 260 mm, Femur length FL 55 mm, Clinical GA (optional, by LMP / first-trimester CRL) 28 wk → Result: Composite US gestational age 30w1d (BPD+HC+AC+FL)（Estimated fetal weight EFW: 1512 g (±~15%, Hadlock4 four-param), BPD implied GA: 32w1d, HC implied GA: 32w0d）