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Estimated Fetal Weight (Hadlock)

Hadlock 1985 regression + Hadlock 1991 weight standard

Computes sonographic estimated fetal weight from standard biometry using the Hadlock 1985 log10 regressions (BPD/AC/FL or HC/AC/FL), and — when gestational age (24–42 weeks) is given — reports the percentage of the expected 50th-percentile weight and an approximate growth percentile from the Hadlock 1991 in-utero weight standard.

Also searched as: obstetric · efw · biometry · growth · sga · lga · pregnancy

Hadlock formula (1985)

Both regressions are from Hadlock et al., Am J Obstet Gynecol 1985;151:333-7; measurements in cm.

Abdominal circumference (AC)
cm
Femur length (FL)
cm
Biparietal diameter (BPD)

Required for the BPD + AC + FL formula.

cm
Head circumference (HC)

Required for the HC + AC + FL formula.

cm
Gestational age source (optional — enables percentile reporting)

When an early dating or NT scan has already fixed the EDD, use that mode instead of re-deriving GA from LMP — LMP dates are frequently unreliable.

Gestational age — weeks

Optional; enables percentile and %-of-expected reporting (table covers 24–42 weeks).

weeks
Gestational age — additional days
days
Information
Incomplete input
  • The following information is still needed: abdominal circumference (cm), femur length (cm), biparietal diameter (cm).

How this tool works

Hadlock and colleagues derived log-linear regressions of birth weight on fetal biometric measurements (in centimeters). This tool implements two verified 1985 equations: log10(EFW) = 1.335 − 0.0034·AC·FL + 0.0316·BPD + 0.0457·AC + 0.1623·FL (biparietal diameter version) and log10(EFW) = 1.326 − 0.00326·AC·FL + 0.0107·HC + 0.0438·AC + 0.158·FL (head circumference version). Hadlock regressions carry an error of roughly ±15% (95% limits), so small differences between formulas are not clinically meaningful. If a gestational age within the table range (24–42 weeks) is supplied, the EFW is compared with the Hadlock 1991 sonographic weight standard: the percentage of the expected median weight is shown, and an approximate percentile is estimated by piecewise-linear interpolation across the published 3rd/10th/30th/50th/70th/90th/97th percentile weights. Weight below the 10th percentile is flagged as small-for-gestational-age range and above the 90th as large-for-gestational-age range. Avoid BPD-containing formulas when head shape is abnormal (e.g., marked dolichocephaly).

References

Implemented from the cited published sources. Educational use only; confirm against current guidelines before clinical use.

Clinical questions that use this

Vetting guides that reach for this tool.

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