Fetal Weight Percentile Calculator
Calculate estimated fetal weight (EFW) percentile for gestational age, using Hadlock-derived reference means.
What is Fetal Weight Percentile?
Estimated fetal weight (EFW) is one of the most important measurements in late pregnancy. Percentiles below 10 raise concern for fetal growth restriction (FGR), which is associated with stillbirth, neonatal complications and long-term metabolic disease. Percentiles above 90 (macrosomia) raise the risk of difficult delivery, shoulder dystocia and neonatal hypoglycaemia. Serial measurements are far more useful than single readings.
How is it calculated?
EFW is calculated by the radiologist or sonographer from biometric measurements (biparietal diameter, head circumference, abdominal circumference, femur length) using the Hadlock formula. The percentile is computed by comparing EFW to the gestational-age-specific reference mean and standard deviation.
Frequently Asked Questions
- Is one low percentile concerning?
- One low reading is less concerning than a downward trend across scans.
- Are EFW estimates accurate?
- Within ~10% in typical late-pregnancy scans.
- Can fetal percentile differ from birth percentile?
- Yes — final birth weight is the truer measure.
- What if EFW is above 90th percentile?
- Clinicians may consider gestational diabetes screening and delivery planning.