Logo

OpiCalc

FavoritesSpecialtiesDrugsGuidelinesMost Used

Quick Access

Favorites
Most Used

All Specialties

OpiCalc Logo
Clinical CalculatorsDrugsGuidelines
SpecsDrugsGuides
APGAR ScoreAssisted Delivery (FIGO)BPP (Manning Score)Bishop ScoreCARPREG II Cardiac RiskCervical Cancer StagingContraceptive Pearl IndexDoppler Matrix (UA/MCA)EFW (Hadlock)Endometrial StagingEndometrial ThicknessFGR Criteria (Consensus)FSFI (Sexual Function)Ferriman-Gallwey ScoreFetal Anemia (MCA PSV)GDM Diagnostic CriteriaGPA History IndicatorGail Model Breast RiskGestational Dating (LMP)HIV PMTCT ProtocolIOTA Simple RulesIVF Due Date & AMHIron Deficit (Ganzoni)Labour Progress (WHO)Maternal Sepsis (qSOFA)O-RADS ClassificationOvarian Cancer StagingPAS Hemorrhage RiskPPH Protocol (FIGO)Preeclampsia (ACOG)Rho(D) Dose (K-B)Rotterdam PCOS CriteriaSyphilis ManagementTORCH FrameworkVBAC Success ProbabilityVulvar Cancer StagingWeight Gain (IOM)mWHO Cardiac Risk
OpiCalc Logo

OpiCalc

Easy, fast, and private medical tools for clinicians. Always free.

No Login Required
Ready for the Bedside

Resources

About UsEditorial PolicyMedical DisclaimerPrivacy PolicyTerms of UseCookie Policy

Support

Contact Us

Clinical Notice:OpiCalc is not a substitute for professional clinical judgment. Always verify dosages and guidelines.

OpiCalc © 2026

•

All Rights Reserved

EFW (Hadlock)

Hadlock EFW Model (4-Param)

Hadlock's Model 4 (BPD, HC, AC, FL) is widely considered the most accurate for Western fetal demographics.

Guidelines & Evidence

Verified

Last Review: 2026-07-17

When to Use

Primary Clinical Uses

Baseline fetal weight estimation across the 2nd and 3rd trimesters
Screening for Fetal Growth Restriction (FGR / SGA) via mapping to growth charts
Assessing likelihood of macrosomia in diabetic pregnancies or post-dates

How it Works

Hadlock IV Formula Parameters

Biparietal Diameter (BPD)
Head Circumference (HC)
Abdominal Circumference (AC)
Femur Length (FL)

Underlying Math

Log10(EFW) = 1.3596 - 0.00386(AC × FL) + 0.0064(HC) + 0.00061(BPD × AC) + 0.0424(AC) + 0.174(FL)

Clinical Pearls

Clinical Pearls

Abdominal Circumference (AC) is the single most sensitive parameter for detecting altered fetal nutritional status (liver size/glycogen).
Femur Length (FL) is generally the most preserved metric in asymmetrical growth restriction (brain-sparing effect).

Known Limitations

Hadlock algorithms inherently carry a ~10-15% margin of error on absolute weight. A 4000g estimate could realistically range from 3400g to 4600g.
Severe oligohydramnios mechanically flattens the fetal abdomen, artificially shrinking AC and drastically underestimating EFW.
Maternal obesity heavily degrades image quality and the reliability of caliper placement.

Next Steps

Risk Stratification (General Guidelines)

01
Plot EFW on a validated local population curve (e.g., Williams, WHO, or INTERGROWTH-21st).
02
If < 10th percentile: Assess for SGA/FGR. Initiate umbilical artery Dopplers and frequent fluid checks.
03
If > 90th percentile: Suspect macrosomia/LGA. Optimize glycemic control, evaluate for shoulder dystocia risk, discuss mode of delivery if >4500g (or >4000g in diabetics).

The Evidence

Historical Foundation

Estimation of fetal weight with the use of head, body, and femur measurements—a prospective study.

Hadlock FP et al. • Am J Obstet Gynecol.. 1985;Established the iconic 4-parameter model (Hadlock 4) which remains the global standard for sonographic EFW calculations almost 40 years later.

Origins & History

Dr. Frank P. Hadlock

Dr. Hadlock was a legendary diagnostic radiologist at Baylor College of Medicine. His relentless mathematical modeling in the 1980s formed the absolute bedrock of modern obstetrical ultrasound biometric screening.

Last Comprehensive Review: 2026-07-17

In Recent Clinical News

Scanning Medical Journals

No new significant updates or guidelines matching this topic were found today. We will check again soon.