New sonographic method for fetuses with small abdominal circumference improves fetal weight estimation

Area of Science:

• Obstetrics and Gynecology
• Medical Imaging
• Fetal Medicine

Background:

• Accurate fetal weight estimation is crucial for obstetric management.
• Existing formulas often lack precision, particularly for fetuses with smaller abdominal circumferences (AC).
• The abdominal circumference significantly influences fetal weight calculations in common equations.

Purpose of the Study:

• To develop and evaluate novel formulas for improved fetal weight estimation.
• To specifically address the challenge of estimating weight in fetuses with a small abdominal circumference (AC ≤ 29.0 cm).

Main Methods:

• A study of 323 singleton pregnancies meeting specific inclusion criteria (e.g., AC ≤ 29.0 cm, no malformations).
• Development of two 'best-fit' formulas using forward regression analysis.
• Comparison of new formulas against standard equations using percentage error, absolute percentage error (APE), and limits of agreement (LOA).

Main Results:

• The new formulas demonstrated no systematic error, unlike routine methods that underestimated fetal weight.
• The novel equations achieved the lowest median absolute percentage errors (7.13% and 7.16%).
• New formulas provided the narrowest limits of agreement and included significantly more cases across discrepancy levels (5-20%) compared to existing methods.

Conclusions:

• Specifically designed equations enhance fetal weight estimation accuracy for fetuses with an abdominal circumference (AC) ≤ 29.0 cm.
• The developed formulas offer a more reliable tool for obstetricians.
• Formula II is recommended for optimal fetal weight estimation in this cohort.