Accuracy of Sonographic Fetal Weight Prediction – Evaluation of Sex-specific Formulas

Abstract: Traditional evaluation of fetal weight is performed by means of ultrasonography and mathematical formulas using combinations of biometric parameters, like abdominal circumference (AC), head circumference (HC), biparietal diameter (BPD), femur length (FL). It was recently shown that mentioned parameters and intrauterine growth patterns demonstrate gender-related differences. These reports were used to develop new formulas which take into account the influence of fetal sex. The aim of this paper was to determine the accuracy of ultrasound fetal weight estimations with use of many different formulas, test sex-specific formulas against established methods and to compare their precision in different weight groups. This retrospective study included 97 singleton fetuses with birth weight (BW) between 1040 g and 4740 g and ultrasound examination within 7 days before delivery. Estimated fetal weight (EFW) was calculated by Hadlock, Shepard, Campbell and Merz formulas and sex-specific models of Schild and Melamed. EFW was confronted with actual BW. Achieved results were compared in a few groups considering gender and BW. The accuracy of fetal weight estimations turned out to be higher for males regardless of the used formula. For the whole study population, the best accuracy was proved for Melamed formulas and the worst for models of Shepard and Merz. The highest precision of predictions was revealed in the group of newborns with BW 2500 – 3999 g. Estimated errors for low birth weight (LBW) infants and macrosomic fetuses were more significant. In most cases, new sex-specific formulas provide smaller mean errors than established methods.


Agnieszka Szpak, Kinga Simura, Jerzy Florjanski MD, PhD

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