J. Siemer

Weight estimation by three‐dimensional ultrasound imaging in the small fetus

To improve birth weight estimation in fetuses weighing ⩽ 1600 g at birth by deriving a new formula including measurements obtained using three‐dimensional (3D) sonography.

Specific weight formula for fetuses with abdominal wall defects

To develop and to evaluate a specific sonographic weight formula for fetuses with abdominal wall defects.

What are the limits of accuracy in fetal weight estimation with conventional biometry in two-dimensional ultrasound? A novel postpartum study

Commonly used formulae for fetal weight estimation, including combinations of several biometric parameters, lack accuracy despite efforts to improve them. This study aimed to investigate the limits of fetal weight estimation based on conventional biometric parameters on two‐dimensional (2D) ultrasound by developing and evaluating new weight equations using postpartum biometric parameters.

Increased Accuracy of Fetal Weight Estimation with a Gender-Specific Weight Formula

Objective: To test whether Schild’s sex-specific formula for estimating fetal weight is more accurate than commonly used regression formulae. Methods: The gender-specific formula and 10 widely used equations were evaluated in a group of 989 pregnancies. Each fetus underwent ultrasound examination with complete biometric parameters within 7 days before delivery. Results: Over the whole weight range and in the subgroup of newborns with a birth weight between 2,500 and 3,999 g, the sex-specific weight formula from Schild demonstrated the best level of accuracy. For infants with a birth weight of less than 2,500 g as well as for macrosomic newborns, the gender-specific formula did not improve fetal weight estimation. Conclusion: In pregnancies where fetal gender is known, Schild’s regression formula should be used when fetal weight lies within the range of 2,500–3,999 g.

Do Specific Weight Formulas for Fetuses ≤ 1500 g Really Improve Weight Estimation?

PURPOSE In addition to gestational age, fetal weight is an important predictive parameter for neonatal morbidity and mortality in very small fetuses. In order to improve weight estimation, specific weight formulas for fetuses under 1500 g have been introduced by several authors. The aim of the present study was therefore to compare specific weight equations for fetuses under 1500 g with widely used methods that were designed for the whole fetal weight range. MATERIALS AND METHODS 459 pregnancies were included in order to evaluate six widely used formulas and four formulas specifically designed for very small fetuses. The inclusion criteria were a singleton pregnancy, birth weight equal to or less than 1500 g, ultrasound examination with complete biometric parameters during the 7 days prior to delivery, and an absence of structural or chromosomal malformations. RESULTS All formulas, except the Hadlock equations, demonstrated a significant systematic error. Regarding the random error, it was similar for most of the methods. The Scott formula showed the narrowest limits of agreement. At a discrepancy level of 5 % and 10 % between estimated fetal weight and actual birth weight, one of the Hadlock formulas included the most cases. CONCLUSION Weight formulas, specifically designed for very small fetuses, do not improve sonographic weight estimation substantially. Among these formulas, the Scott equation was the most accurate one. However compared to the widely used Hadlock formulas, it was not favorable.

How Good is Fetal Weight Estimation Using Volumetric Methods

PURPOSE Birth weight is an important predictive parameter for neonatal morbidity and mortality, and accurate estimation of fetal weight is therefore a valuable tool for determining the further obstetric management. Many sonographic weight formulas have been introduced. Most of these widely accepted formulas were derived from non-linear regression analysis. Only few formulas have been constructed using other methods, such as the physically based volumetric method based on routine two-dimensional biometric parameters in the fetus. The rationale for calculating fetal weight from volumetric measurements was that weight should to be directly proportional to fetal volume. In a recent review by Dudley, this method was considered to have some advantages in comparison with conventional regression formulas. However, to the best of our knowledge, none of the published volumetric formulas has ever been evaluated in a large population of fetuses. The aim of this study was to compare the volumetry-based formulas with widely accepted weight equations derived from regression analysis. We evaluated weight equations over the whole weight range and in specific weight groups in order to find out whether some equations were preferable in the groups tested. MATERIALS AND METHODS 3975 pregnancies were included in order to evaluate four conventional formulas and four formulas based on volumetric models. The inclusion criteria were a singleton pregnancy, ultrasound examination with complete biometric parameters within 7 days before delivery, and an absence of structural or chromosomal malformations. The equations were compared over the whole weight range and in specific weight groups. RESULTS Over the whole weight range, no single formula was able to offer a substantial advantage. In the small fetus, the Hadlock formula was preferable due to its low level of systematic error. For mid-sized fetuses, the Schild formula should be considered. In macrosomic fetuses, all formulas tended to underestimate the actual birth weight. Here, the best accuracy was achieved using the Merz formula. CONCLUSION Neither a volumetric formula nor a conventional formula proved to be superior over the whole weight range. Within specific weight groups, some formulas showed improved accuracy. However, new approaches such as three-dimensional ultrasonography need to be pursued further in order to achieve better results in fetal weight estimation.

Gender-Specific Weight Estimation of Fetuses between 2,501 and 3,999 g – New Regression Formulae

Objective: To develop new gender-specific regression formulae to estimate fetal weight focusing on a particular weight range from 2,501 to 3,999 g. Methods: 3,254 singleton pregnancies were included to generate new regression formulae for female and male fetuses, and to evaluate their accuracy. Results: In comparison with commonly used formulae, the new gender-specific and weight-range-specific method of fetal weight estimation provided greater accuracy. The mean absolute error was less than 7%. Conclusions: When properly used, the new formulae can improve the accuracy of weight estimations in fetuses between 2,501 and 3,999 g.

Comparison of Different Sonographic Methods to Determine Fetal Abdominal Circumference

Purpose: In modern obstetric management, accurate estimation of fetal weight is an important prognostic parameter of neonatal morbidity and mortality, and a valuable tool for determining further treatment. Fetal abdominal measurements, mostly abdominal circumference (AC), are not only included in the majority of commonly used weight equations, but also have the greatest impact on weight estimation. This therefore underlines the importance of accurate determination of the AC. The aim of our study was to evaluate which method for AC calculation is the most accurate one and thereby gives the best results for fetal weight estimation. Materials and Methods: This prospective study included 239 term pregnancies. Inclusion criteria were a singleton pregnancy and ultrasound examination with complete fetal biometric parameters within 3 days of delivery, and absence of structural or chromosomal malformations. For calculation of the sonographic AC, three different methods were used. As a reference method, AC of the infant was determined immediately after birth. The accuracy of fetal weight estimation was determined for all of these methods of AC measurement using a commonly used weight equation. Differences were compared by using percentage error (PE), absolute percentage error (APE), limits of agreement (LOA) and cumulative distribution. Results: The ellipse region-of-interest (ROI) method showed the best results of all sonographic methods. For estimating fetal weight, it had the lowest median APE of the sonographic methods and the lowest SD of the PE, as well as the narrowest LOA. Regarding the cumulative distribution, ellipse ROI technique included the most cases at all discrepancy levels (5, 10, 15, and 20%). Conclusion: Accurate measurement of fetal AC is important for good fetal weight estimation. The differences between the three techniques were small; however, there was a significant advantage when using the ellipse ROI method.

Fetal Adrenal Haemorrhage – Two-Dimensional and Three-Dimensional Imaging

A case of prenatal adrenal haemorrhage first detected by 2-dimensional and 3-dimensional sonography at 27 weeks’ gestation is reported. Ultrasound examination showed a large cystic mass (32 × 27 × 27 mm) in the right suprarenal region of the fetus. Two weeks later, the mass had slightly increased in size demonstrating hyperechoic areas within the cyst. Further serial ultrasound examinations revealed a progressive organisation of the cystic mass associated with a moderate reduction in size. The diagnosis of adrenal haemorrhage was confirmed by postnatal follow-up sonograms as the mass decreased in size from 28 × 21 × 21 mm on day 1 to 23 × 18 × 17 mm on day 42. Course and sonographic signs were typical for adrenal haemorrhage and the neonate was therefore managed without surgical exploration. The child is developing normally at 6 months of age.

A New Sonographic Weight Formula for Fetuses ≤ 2500 g

PURPOSE Birth weight is an important predictive parameter for neonatal morbidity and mortality in the small fetus. Accurate estimation of fetal weight is therefore a valuable tool for determining the further obstetric management. The majority of studies presenting new formulas have included relatively small samples with a narrow range of birth weights, mostly term fetuses. In a previous study, we evaluated several weight formulas over the whole range of birth weights and in defined subgroups. We were able to show that some regression formulas appeared to be favorable within these subgroups. Notably, the highest levels of inaccuracy were found in the group of infants with a birth weight of less than 2500 g. This led us to hypothesize that a formula based on the lower birth weight group might increase the accuracy of weight estimation. The aim of the present study was therefore to develop a new specific formula for estimating weight in fetuses less than or equal to 2500 g and to compare the new regression formula with commonly used weight equations. MATERIALS AND METHODS This study included 260 pregnancies. The inclusion criteria were a singleton pregnancy; birth weight equal to or less than 2500 g; an ultrasound examination with complete biometric parameters within 7 days prior to delivery; and an absence of structural or chromosomal malformations. The data for the first 130 newborns were used to develop a new formula. The remaining 130 infants were used to evaluate the new regression formula and to compare it to commonly used weight equations. Stepwise regression analysis was carried out with the birth weight as the dependent variable and biometric parameters as independent parameters to obtain the best-fit formula. RESULTS The mean absolute percentage error for the new formula was 7.71 %. Compared to the other formulas, it generated the highest intraclass correlation coefficient. By the limits of agreement, the new formula demonstrated only a slight tendency towards underestimating fetal weight, and it provided the smallest range of all weight equations. CONCLUSION With proper application, our new formula can improve the accuracy of fetal weight estimation.