How to Use Fetal Weight Percentile Calculator
The Fetal Weight Percentile Calculator focuses on how to estimate fetal weight percentile from gestational age and estimated fetal weight. Follow these steps:
- Enter gestational weeks and additional days
- Enter estimated fetal weight in grams from the ultrasound report
- The calculator interpolates p10, p50, and p90 reference bands for the exact gestational age
- Interpret the percentile with awareness that ultrasound fetal-weight estimates have measurement error
Formula & Theory — Fetal Weight Percentile Calculator
The Fetal Weight Percentile Calculator uses the following calculation logic:
gestational age in weeks = completed weeks + days / 7
Interpolate p10, p50, and p90 at that gestational age.
If EFW is between p10 and p50:
percentile = 10 + 40 × (EFW − p10) / (p50 − p10)
If EFW is between p50 and p90:
percentile = 50 + 40 × (EFW − p50) / (p90 − p50)Fetal weight percentile is anchored to gestational age because expected fetal weight rises quickly across pregnancy. Interpolation lets the calculator estimate the reference bands between whole-week table values.
Use Cases for Fetal Weight Percentile Calculator
The Fetal Weight Percentile Calculator is most useful in these situations:
- Obstetric ultrasound education.
- Explaining p10 and p90 fetal growth thresholds.
- Discussing why a small gestational-age correction can change fetal percentile.