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 records and sonograms were reviewed for 68 fetuses born between 14 and 24 weeks with known actual birthweight, no congenital anomalies, and biometric 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, standard 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 regression analysis. Results: A previously published formula using abdominal circumference (AC) and femur length (FL) was better than the biparietal diameter (BPD) and AC formula in all. respects and better or comparable to formulas using three or more parameters. Three new formulas were derived using head circumference (HC) and FL to obtain the best predicted birthweight. Conclusion: For estimation of fetal weight in second trimester fetuses, one of the previously published formulas using AC and FL was reasonably accurate, The new HC and FL formula's accuracy should be studied prospectively. Second trimester EFW curves may be useful to identify fetuses at risk for impaired growth.