Sonographic Weight Estimation in Small-for-Gestational-Age Fetuses

Area of Science:

• Perinatology
• Medical Imaging
• Fetal Medicine

Background:

• Accurate fetal weight estimation is critical for managing pregnancies, especially those involving small-for-gestational-age (SGA) fetuses.
• Distinguishing between symmetric and asymmetric SGA fetuses is important for appropriate clinical management.
• Existing sonographic weight estimation (WE) models may have varying accuracy in SGA populations.

Purpose of the Study:

• To evaluate the accuracy of 14 sonographic weight estimation (WE) models for small-for-gestational-age (SGA) fetuses.
• To compare the performance of these models between symmetric and asymmetric SGA fetal subgroups.
• To identify the most accurate WE formula for SGA fetuses.

Main Methods:

• Retrospective analysis of 898 SGA fetuses using 14 sonographic weight estimation (WE) formulas.
• Subgroup analysis of 750 symmetric SGA and 148 asymmetric SGA fetuses.
• Asymmetric SGA defined by a head circumference to abdominal circumference ratio above the 95th percentile.
• Accuracy assessed using Mean Percentage Error (MPE), Median Absolute Percentage Error (MAPE), and proportion within 10% of actual birth weight.

Main Results:

• Significant differences in WE accuracy were observed between asymmetric and symmetric SGA subgroups.
• Most formulas underestimated fetal weight in asymmetric SGA fetuses, with MPE closer to zero.
• In symmetric SGA fetuses, common formulas overestimated fetal weight.
• The Sabbagha equation demonstrated the highest accuracy (MPE 1.7%, MAPE 6.0%) overall.

Conclusions:

• Accurate sonographic weight estimation (WE) for small-for-gestational-age (SGA) fetuses is achievable with the Sabbagha formula.
• Clinicians must recognize the distinct WE performance characteristics in symmetric versus asymmetric SGA fetuses.
• Tailoring WE approaches based on SGA type can improve diagnostic precision.