ACCURACY OF FETAL WEIGHT ESTIMATION FORMULAS IN THE 2ND-TRIMESTER

Objective: To examine the accuracy of previously published formulas to estimate fetal weight (EFW) in second trimester fetuses and to derive new formulas to EFW in the second trimester. Methods: Obstetrical rec ords and sonograms were reviewed for 68 fetuses born between 14 and 24 weeks with known actual birthweight, no congenital anomalies, and bio metric data within 4 days of birth. Six previously published formulas using a combination of two or more biometric parameters were examined, Birthweight predictive accuracy was evaluated by mean residual, stand ard error (SE) residual, mean absolute residual, SE absolute residual, the mean deviation of the signed percent error, mean absolute percent error, mean deviation, standard deviation, and EFW prediction within 5, 10, and 20%. New formulas to EFW were derived by stepwise regressio n analysis. Results: A previously published formula using abdominal ci rcumference (AC) and femur length (FL) was better than the biparietal diameter (BPD) and AC formula in all. respects and better or comparabl e to formulas using three or more parameters. Three new formulas were derived using head circumference (HC) and FL to obtain the best predic ted birthweight. Conclusion: For estimation of fetal weight in second trimester fetuses, one of the previously published formulas using AC a nd FL was reasonably accurate, The new HC and FL formula's accuracy sh ould be studied prospectively. Second trimester EFW curves may be usef ul to identify fetuses at risk for impaired growth.