New Sonographic Method for Fetuses with a Large Abdominal Circumference Improves Fetal Weight Estimation

Zusammenfassung

Ziel: Das Geburtsgewicht ist ein wichtiger prognostischer Parameter. Die gebräuchlichen Gewichtsformeln haben eine gewisse Messungenauigkeit. Der sonografische Abdomenumfang (AU) des Feten ist in den meisten Gewichtsgleichungen enthalten und hat den größten Einfluss auf die Gewichtsschätzung. Bei kleinem AU hat eine speziell hierfür entwickelte Formel die Gewichtsbestimmung verbessert. Das Ziel war es daher, eine neue Gewichtsformel für Feten mit großem AU (≥ 36,0 cm) zu entwickeln, um die Gewichtsschätzung zu optimieren. Material und Methoden: Es wurden 830 Schwangerschaften eingeschlossen. Einschlusskriterien waren eine Einlingsschwangerschaft, eine komplette Ultraschallbiometrie mit einem sonografischen AU ≥ 36,0 cm innerhalb von 7 Tagen vor Geburt sowie ein Fehlen von strukturellen oder chromosomalen Anomalien. Die Genauigkeit zweier „Best-fit“-Formeln, bestimmt mittels Vorwärts-Regressionsanalyse, wurde mit gängigen Gewichtsformeln anhand des prozentualen Fehlers (PE), des absoluten prozentualen Fehlers (APE), der „Limits of agreement“-Methode (LOA) und der kumulativen Verteilung verglichen. Ergebnisse: Die neue Formel I zeigte keinen systematischen Fehler, im Gegensatz dazu überschätzten die neue Formel II und die Routineformeln das Gewicht signifikant. Die Mediane der APEs waren bei den beiden neuen Formeln am niedrigsten (5,77 und 7,25). Weiterhin wiesen sie die engsten LOA auf. Die neue Formel I schloss bezüglich der kumulativen Verteilung auf allen Ebenen (5 %, 10 %, 15 % und 20 %) die meisten Fälle ein. Schlussfolgerung: Bei Feten mit einem Abdomenumfang von ≥ 36,0 cm hilft die speziell entwickelte Formel I, die fetale Gewichtsschätzung zu verbessern.

Abstract

Purpose: Birth weight (BW) is an important prognostic parameter for neonatal morbidity and mortality. Commonly used weight formulas lack accuracy, especially at the lower and upper end of the fetal weight range. Fetal abdominal circumference (AC) as part of most of the commonly used equations has the greatest impact on weight estimation. It has been shown that formulas specifically designed for a small fetal AC can improve weight estimation. The aim was to find out whether a new formula specifically designed for fetuses with a large AC may also improve weight determination. Materials and Methods: The study included 830 singleton pregnancies. The inclusion criteria were ultrasound examination with complete biometric parameters and an AC ≥ 36.0 cm within 7 days of delivery, and an absence of structural or chromosomal malformations. Two “best-fit” formulas were derived by forward regression analysis. The accuracy of the new formulas was compared with commonly used weight equations using percentage error (PE), absolute percentage error (APE), limits of agreement (LOA) and cumulative distribution. Results: New formula I had no systematic error while new formula II and the routine methods significantly overestimated fetal weight. The medians of the APE were the lowest among the new equations (5.77 and 7.25). The new formulas also demonstrated the narrowest LOA. Importantly, at all discrepancy levels (5 %, 10 %, 15 %, and 20 %), new formula I included significantly more cases than the commonly used methods. Conclusion: These specifically designed equations help to improve fetal weight estimation for fetuses with an AC ≥ 36.0 cm. For optimal weight estimation, we recommend using new formula I.

Key words

weight formula - abdominal circumference - macrosomia - fetal weight estimation

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