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.
Section 4
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).
Section 5
Evidence Appraisal
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.
Section 6
Literature
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.
