OBJECTIVETo analyze the factors affecting the accuracy of Osaka formula multiparameter ultrasound-based fetal mass estimation, thereby establishing new formulas to improve the accuracy of the estimation.

METHODSA retrospective review was conducted among 519 healthy women with singleton pregnancy. Three days before the delivery (between 37 and 42 weeks' gestation), ultrasonic measurement of the fetal weight and other indices of the fetus was routinely performed. Correlation and multiple linear stepwise regression analysis were used to correct the 3 equations, which, along with Osaka University formula, were used to predict another 219 fetuses' birth weight. The coincidence rate of the predicted value and with the actual birth weight, and the absolute error and relative error were compared between the equations.

RESULTSThe fetal abdominal area (AA) and abdominal circumference (AC) showed the most conspicuous influence on the estimated fetal birth weight, and fetal humerus length (HL) was more sensitive than femur length (FL) for the estimation. Three new regression equations were established, among which the equation 2 (fetal birth weight=1082.859+4.116xAAxHL) showed the best accuracy in clinical prediction.

CONCLUSIONAA,AC and HL are more sensitive indices for estimation of the fetal birth weight, and the equation 2 established in this study still awaits further verification for its clinical value.