Estimation of fetal weight by ultrasound measurement. II. Clinical application of a new formula.

A formula for the estimation of fetal weight combining real-time ultrasonic measurements of the fetal biparietal diameter (BPD) and the abdominal transverse diameter (ATD) was applied to 264 unselected pregnancies. The measurements were performed within 4 days of delivery. The weight range of the fetal birth weights was 850-5100 g. The fetuses were divided into five weight groups according to their birth weight and the prediction errors (estimated weight minus birth weight) analyzed. For the whole group the SD of prediction errors was 258 g. SD of prediction errors increased with the increase in fetal weight. The formula did not significantly over- or underestimate fetal weight in any of the weight groups. The results obtained for the growth-retarded fetuses and the fetuses in breech position did not differ from the results overall. There was no significant difference between mean prediction errors or variances for the measurements performed by four different observers. It is concluded that the formula can be readily applied in daily clinical practice. It provides adequate information on fetal weight in the weight range 900-5000 g. For practical application a nomogram has been developed.