Estimating Fetal Weight
Estimated fetal weight (EFW) is calculated from ultrasound measurements using formulas like Hadlock. Common measurements include biparietal diameter (BPD - head width), head circumference (HC), abdominal circumference (AC), and femur length (FL). These are combined to estimate weight.
Accuracy of Estimates
EFW has a margin of error of ±10-15% in the third trimester. Accuracy is better for average-sized babies and decreases for very large or small babies. Factors affecting accuracy include maternal obesity, amniotic fluid levels, fetal position, and ultrasound quality.
Why Estimate Fetal Weight?
Monitors appropriate growth for gestational age, detects growth restriction (IUGR) or macrosomia (large baby), helps plan delivery method (very large babies may require C-section), and identifies potential complications. Serial measurements over time are more valuable than single estimates.
Quick Tips
- BMI alone doesn't reflect overall health
- TDEE varies based on activity level
- Consult a healthcare professional for medical decisions
Frequently Asked Questions
Typically within ±10-15%. Accuracy is best for average-sized babies in good conditions.
Small measurement differences cause large weight differences. Operators and machine quality vary.
Estimates within 1-2 weeks of delivery are most accurate but still have 10-15% error.
Varies by gestational age. At 40 weeks, average is 3000-3500g (6.6-7.7 lbs).
One measurement isn't definitive. Your doctor will monitor trends and consider other factors.