To assess the accuracy of weight estimation (WE) in fetuses with breech presentation and to compare it directly with a control group of fetuses in vertex presentation. In a retrospective cohort study, the accuracy of WE in fetuses with breech presentation (n = 244) was evaluated using eight sonographic models and was compared with a control group of fetuses in vertex presentation (n = 244). Each fetus underwent ultrasound examination with complete biometric parameters within 7 days before delivery. The accuracy of the different formulas was compared using means of percentage error (MPE), a measure that reflects systematic error; standard deviation values of MPEs, a measure for random error; medians of absolute percentage error (MAPE), which take both the systematic and random error into account and the percentage of fetal WEs falling within a 10 % range of the actual birth weight. Significantly lower (more negative) MPE values were found in the breech group with the Hadlock (AC, FL) formula, whereas no significant differences were seen with any of the other equations. When compared to zero, in the breech group, a significant systematic error was found with five formulas, while in the control group a significant systematic error was found with three equations. With regard to random error and MAPE, no significant differences were found between the two groups, irrespective of the formula applied. Generally, in both groups, formulas based on three or four biometric indices were more accurate in detecting fetal weight than formulas with only one or two parameters. Weight estimation in fetuses with breech presentation was as accurate as weight estimation in fetuses with vertex presentation. Using the currently available, well-established formulas should therefore also be appropriate for WE in fetuses with such malpresentations.
