Establishment of a New Equation for Ultrasonographic Estimated Foetal Weight in Chongqing: a Prospective Study

Background: Variations in foetal growth between populations should not be ignored, and a single universal standard is not appropri-ate for everyone. Therefore, it is necessary to develop a new ultrasound estimation equation that adapts better to regional population characteristics. The purpose of this study was to create a new equation for ultrasound estimation of foetal weight according to the local population in Chongqing and compare it with representative equations. Methods: This prospective study included data on pregnant women who gave birth to a child at full term in our hospital from December 2016 to November 2019. Foetal ultrasound parameters included biparietal diameter (BPD), head circumference (HC), abdominal circumference (AC), and femur diaphysis length (FDL). The foetal weight compensation model was established by using the second-order linear regression model, and then, the foetal weight equa-tion was established by utilizing the multiple reverse elimination regression technique. Last, the absolute error and relative error were used to compare the accuracy of the equations established in this study with representative equations. Results: Through the foetal weight compensation equation, the new equation suitable for Chongqing foetuses was successfully established with the variables of BPD, HC, AC, and FDL. The following foetal weight prediction equation was established in this study: Log10(EFW) = 3.002741 + 0.00005944 x (BPD2) + 0.00000222 x (HC2) - 0.000002078 x (AC2) + 0.00004262 x (FDL2) - 0.008753 x BPD - 0.000884 x HC + 0.003206 x AC - 0.002894 x FDL (BPD: mm; HC: mm; AC: mm; FDL: mm). In the sets established by the 1925 data, the mean absolute error and standard deviation of the estimation error of the new equation were 178.9 g and 140.3 g respectively. In the validation sets established with 300 data points, the mean absolute error and standard deviation of the new equation were 173.08 g and 128.59 g respectively. Com-pared with representative equations, the mean absolute error and the standard deviation of the new equation were the lowest. The equation established in this study better predicted foetal weight (p < 0.001). Conclusions: According to the local population characteristics of Chongqing, this study created a foetal weight estimation equation that is more accurate and suitable. This equation is clinically valuable for the monitoring and management of foetal weight.