Objective To apply the cumulative summation (CUSUM

respectively; P < 0.0005), whereas the performance of the Nahum and Stanislaw equation was similar but not superior to ultrasound alone (AUC 0.895, respectively; P > 0.05

MS-AFP level in the second trimester is still an important indicator of fetal surface malformations; however, ultrasound still outweighs as a screening method. Nevertheless, pregnant women with elevated MS-AFP values and with no sonographically detected fetal malformations should additionally receive the third trimester ultrasound examination to exclude other possible complications of pregnancy.

Use of the CUSUM technique analysing the quality of sonographic NT measurements provides the possibility to prospectively observe the development of the examiner's skills, to maintain competence and to promptly define the time when inaccurate measurements start to occur.

The Hadlock et al. formula tends to underestimate fetal weight, in particular > 3500 g. At the high end of the range, the Merz et al. formula is more accurate, but becomes less so in smaller fetuses. This study was designed to improve fetal weight estimation in fetuses > 3500 g by identifying the fetal biometric parameter providing the most reliable guidance to optimal formula selection. Regression analysis of 12 032 pregnancies showed that multiplication of abdominal circumference by femur length (AC × FL) gave the best choice of appropriate formula: Hadlock for AC × FL< 24 600, Merz for those ≥ 24 600. We then tested this rule, ('Zurich method'), prospectively in 4073 pregnancies, comparing it with the Hadlock, Merz and the Kehl formulas. Birth weights were merged into 7 categories (< 1500 to ≥ 4000 g, interval of 500 g). The percentage error (PE) and absolute percentage error (APE) were calculated. The PE using the Zurich method was lower in both> 3500 g groups than with the Hadlock formula alone (3500 - 3999 g: 0.9 % vs. - 5.3 %, > 4000 g: - 3.2 % vs. - 8.6 %), similar to that with the Merz formula alone, and lower than with the Kehl formulas (3500 - 3999 g: - 9.0 % vs. - 3.2 %, > 4000g: - 5.1 % vs. 0.9 %). The Zurich method and Hadlock formula also shared the lowest PE in the < 1500 g group: 0.2 % vs. 6.8 % (Kehl) vs. 9.6 % (Merz). In terms of APE the Zurich method performed almost as well as the Merz formula in the > 4000 g group, while sharing the lowest value with the Hadlock formula in the< 1500 g group (8.2 % vs. 10.5 % [Kehl], 23.6 % [Merz]). The Zurich method uses a pivotal value of the biometry parameter AC × FL to switch between formulas and corrects for the errors of the Hadlock formula in fetuses ≥ 3500 g and those of the Merz formula in fetuses< 3500 g.