Selection of appropriate ultrasound methods for the estimation of fetal weight.

Many methods for fetal weight estimation have been proposed. Earlier formulae were derived solely by regression analysis but more recently formulae based on physical models have been developed. Some of these formulae are lengthy and difficult to use. The main purpose of this study was to evaluate a concise area based formula developed several years ago against popular and recently published formulae. Data from 388 patients over a 5 year period were collected from clinically required ultrasound scans performed within 10 days of delivery. Four of the seven formulae evaluated proved to be equally accurate over a broad range of birthweights (mean absolute deviations 245-249 g), including the area based formula and a circumference based formula derived from it. On the grounds of the number of terms, the precision of coefficients, the physical meaning and the greater accuracy of individual area measurements compared with those derived from circumference, the area based formula should be the method of choice.