Fetal Weight Estimation in Extreme Macrosomia (≥ 4,500 g): Comparison of 10 Formulas

 

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Abstract

Purpose: The aim of this retrospective study was to compare the accuracy of 10 commonly used weight estimation formulas in a group of fetuses with extreme macrosomia ( ≥ 4 500 g).

Materials and Methods: Ten formulas were evaluated in a group of 174 fetuses with a birth weight (BW) ≥ 4 500 g. Each fetus underwent ultrasound examination with complete biometric parameters within 7 days of delivery. The accuracy of the different formulas for fetal weight estimation (EFW) was compared by mean percentage error (MPE), median of the absolute percentage error (MAPE), the “limits-of-agreement” method and the percentage of EFW falling within the 10 % range of the true birth weight.

Results: MPE showed the largest deviation from zero with the Schild formula (MPE – 15.43 %) and the Shepard formula (MPE + 6.08 %) and was closest to zero with the Hadlock II formula (MPE – 5.34 %). The MPE of all formulas showed significant bias when compared to zero. All tested formulas, except the Shepard and Shinozuka equations, significantly underestimated fetal weight. The lowest MAPE was found for the Merz formula (7.23 %). The Hadlock II formula obtained the highest percentage of EWF within the 10 % range of the true birth weight (66.1 %).

Conclusion: Exact weight estimation in extreme macrosomia remains an unsolved problem, and can therefore only conditionally provide a sufficient basis for clinical decision processes.

Zusammenfassung

Ziel: Ziel dieser retrospektiven Studie war der Vergleich der Genauigkeit von 10 gängigen Gewichtsschätzungsformeln in einer Gruppe von Feten mit stark ausgeprägter Makrosomie ( ≥ 4 500 g).

Material und Methoden: Verglichen wurden 10 Formeln in einer Gruppe von 174 Feten mit einem Geburtsgewicht ≥ 4 500 g. Der Zeitabstand zwischen der vollständig durchgeführten Biometrie und der Entbindung lag bei allen Feten unter 8 Tagen. Um die Genauigkeit der verschiedenen Formeln zu testen und zu vergleichen, wurden folgende Parameter berechnet: mittlerer relativer Fehler (MPE), Median des absoluten Fehlers (MAPE), „limits-of-agreement“ und der Prozentsatz an Gewichtsschätzungen, der innerhalb 10 % des tatsächlichen Geburtsgewichtes lag.

Ergebnisse: Der MPE zeigte die größten Abweichungen bei Verwendung der Schild Formel (MPE – 15,43 %) und der Shepard Formel (MPE + 6,08 %), wohingegen die Hadlock II Formel (MPE – 5,34 %) die geringsten Abweichungen aufwies. Beim Vergleich gegen null zeigte der MPE aller Formeln einen signifikanten Fehler. Mit Ausnahme der Shepard und Shinozuka Formeln wurde das fetale Gewicht von allen Formeln signifikant unterschätzt. Während die Merz Formel den niedrigsten MAPE aufwies (7,23 %), ergab sich für die Hadlock II Berechnungen der höchste Prozentsatz an Gewichtsschätzungen, innerhalb 10 % des tatsächlichen Geburtsgewichtes (66,1 %).

Schlussfolgerung: Eine genaue Gewichtsschätzung, insbesondere bei den stark makrosomen Feten, ist mit den vorhanden Formeln nicht möglich und kann daher nur bedingt eine suffiziente Grundlage für klinische Entscheidungsprozesse darstellen.

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