An investigation of fetal growth using serial ultrasound data

Serial ultrasonic measurements were performed in 67 Caucasian fetuses from 20 weeks' gestation until term to derive reference standards for abdominal circumference (AC) and estimated fetal weight (EFW). The variances of both AC and EFW increased with gestational age. Four mathematical models (linear, quadratic, Gompertz and Rossavik) were fitted to the log(10)(AC) and log(10)(EFW) data from each fetus using least squares regression analysis. The standard deviations of the residual error were greatest for the linear model. The linear model also overestimated the final log(10)(AC) while the linear, Gompertz and Rossavik models all overestimated the final log(10)(EFW) when these data were omitted from the fitting process. The individual quadratic constants were, therefore, used to produce 67 individual growth curves. Values of log(10)(AC) and log(10)(EFW) for each fetus at exact gestational ages between 20 and 40 weeks were derived by interpolation; the mean and standard deviation values were then used to derive centile ranges for abdominal circumference and estimated fetal weight. These standards should prove useful in the assessment of fetal growth.