Ultrasonographic estimation of fetal weight during labour. Evaluation and comparison of two formulae

Estimation of fetal weight is a major component of obstetric practice and is important in determining management of the high-risk patient in particular. Many patients at high risk for perinatal morbidity and mortality present for the first time in established labour. As clinical methods in these circumstances are of limited accuracy, ultrasonography is increasingly being used for this purpose. The commonly used formulae relating ultrasound measurements to fetal weight were derived from a different population from our at-risk population, and we therefore measured abdominal circumference and biparietal diameter in 51 patients to assess the accuracy of two such formulae. While one of the formulae was superior to the other, the overall accuracy of both was disappointing and we feel that ultrasonographic estimation of fetal weight in labour is of limited value.