To determine the value of principal component analysis in the combined method of three-dimensional ultrasonography assessing fetal limb volume and circumference and conventional two-dimensional ultrasonography for prediction of birth weight in southern Chinese population.

A prospective study was performed on single pregnant women in third trimester. Three- and two-dimensional ultrasonography for fetal biometric parameters were measured within 7 days of delivery. Stepwise linear regression were used to develop a new prediction model based on values from limb parameters and traditional measurements in development group. Estimated and actual birth weight were compared between the new model and previously published formulas on absolute error and percentage error. The accuracy of the model in predicting fetal birth weight was reassured by validation group.

Inclusion Criteria:

• The inclusion criteria consisted of well-defined gestational age (GA), singleton pregnancy and delivery in our hospital within 7 days from the scan performed for acquisition of 2D and 3D ultrasonographic data.

Exclusion Criteria:

• The exclusion criteria were equivocal GA, multiple pregnancy, fetal severe malformation detected by prenatal ultrasonographic scans, delivery more than 7 days after the scan of 2D and 3D ultrasonography, and delivery in other institutions.