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Sonographic Fetal Weight Estimation

Which Model Should Be Used?

Helen Schneider Hospital for Women, Rabin Medical Center, Petah Tikva, Israel; and Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel.

Address correspondence to Nir Melamed, MD, MSc, Department of Obstetrics and Gynecology, Helen Schneider Hospital for Women, Rabin Medical Center, 49100 Petah Tikva, Israel., E-mail: nirm{at}clalit.org.il

Objective. The purpose of this study was to compare the accuracy of different sonographic models for fetal weight estimation. Methods. We evaluated 26 different models using 3705 sonographic weight estimations performed less than 3 days before delivery. Models were ranked on the basis of systematic and random errors and were grouped according to the combination of biometric indices in each model. Cluster analysis was used to compare the accuracy of the different model groups. Results. A considerable variation in the accuracy of the different models was found. For birth weights (BWs) in the range of 1000 to 4500 g, models based on 3 or 4 fetal biometric indices were significantly more accurate than models that incorporated only 1 or 2 indices. The accuracy of weight estimation decreased at the extremes of BWs, leading to overestimation in low-BW categories as opposed to underestimation when the BW exceeded 4000 g. The precision of most models was lowest in the low-BW groups. Conclusions. To improve the accuracy of fetal weight estimation, sonographic models that are based on 3 or 4 fetal biometric indices should be preferred. Recognizing the accuracy and the tendency for underestimation or overestimation of each of the available models is important for the judicious interpretation of fetal weight estimations, especially at the extremes of fetal weight.

Key Words: accuracy • comparison • estimation • fetal • models • weight

Abbreviations: AC, abdominal circumference • ANOVA, analysis of variance • BW, birth weight • BPD, biparietal diameter • EFW, estimated fetal weight • FL, femur length • HC, head circumference