This document presents formulas for estimating fetal weight for fetuses with abdominal wall defects. It compares the mean absolute percentage errors of several existing formulas that use measurements like biparietal diameter, head circumference, abdominal circumference, and femur length to formulas developed specifically for fetuses with abdominal wall defects that use biparietal diameter, occipitofrontal diameter, and femur length. The new formula developed for fetuses with abdominal wall defects that uses these three measurements was found to have the lowest mean absolute percentage error of 8.90% compared to errors ranging from 11.26% to 13.75% for the existing formulas.