Specific weight formula for fetuses with abdominal wall defects.

Objectives: To develop and to evaluate a specific sonographic weight formula for fetuses with abdominal wall defects.

Methods: For formula finding, 380 preterm singleton pregnancies without fetal anomalies were included. Ultrasound examinations with complete biometric parameters were performed within 7 days before delivery. Stepwise regression analysis was carried out with birth weight as the dependent variable and sonographic parameters (abdominal measurements not included) as independent variables to obtain the best-fit formula. The new equation was evaluated in a group of 97 fetuses with either gastroschisis or omphalocele.

Results: In the evaluation group, the mean (SD) percentage error of the new equation was -0.84 (12.03), showing no systematic bias. The mean absolute percentage error was 9.29. The new specific method provided significantly greater accuracy than commonly used formulae.

Conclusions: This specific weight formula for fetuses with abdominal wall defects is an accurate method of estimating fetal weight.