Estimated fetal weight, often abbreviated EFW, is a value calculated from a combination of fetal biometric measurements obtained during ultrasound, typically the biparietal diameter or head circumference, abdominal circumference, and femur length. Several mathematical formulas, such as the Hadlock formula, combine these measurements to produce a weight estimate in grams. The EFW is then compared to gestational age-specific growth charts to determine whether the fetus is appropriately sized, too small suggesting fetal growth restriction, or too large suggesting macrosomia. While the estimated fetal weight has a margin of error of approximately 10 to 15 percent, it is one of the most clinically important calculations in obstetric ultrasound and directly influences management decisions.
Sonography Term