Complete Biometric Parameters Research Articles

Can Sonographic Fetal Biometry Predict Adverse Perinatal Outcome?

To evaluate the association of sonographic fetal biometry (sonographic head circumference (soHC), sonographic abdominal circumference (soAC), estimated fetal weight (EFW)) with mode of delivery and adverse perinatal outcome. Singleton pregnancies with a gestational age ≥ 37 weeks and an ultrasound examination with complete biometric parameters within 7 days before delivery were retrospectively included. The association between soHC, soAC, EFW and fetal (5-min Apgar < 7, pH < 7.1, neonatal intensive care unit (NICU) admission, shoulder dystocia (ShD)) and maternal (obstetric intervention (OI): caesarean or vaginal operative delivery, obstetric anal sphincter injury syndrome (OASIS), postpartum hemorrhage (pph)) adverse outcomes were analyzed using univariate and multivariate logistic regression analyses. 12 396 women were included and 3479 (28.07 %) needed an OI. Multivariate analyses demonstrated significant contributions for the prediction of OI by soHC and soAC, whereas EFW did not reach significance. The highest OR was shown for soHC (1087, p < 0.001). ShD occurred in 73 (0.59 %) of the deliveries. Multivariate analyses showed that significant contributions for the prediction of ShD were provided only by soAC (OR 1460, p = 0.007). For the other maternal and neonatal adverse outcome parameters, no significant association with the biometric measurements could be demonstrated in the multivariate analyses. The overall detection rates for the prediction of adverse perinatal outcome by the different biometric parameters and EFW were poor. Obstetric management decisions should not be based solely on measurements of biometric parameters or EFW.

A New Sonographic Weight Estimation Formula for Fetuses with Congenital Diaphragmatic Hernia.

The accuracy of the sonographic weight estimation (WE) of fetuses with congenital diaphragmatic hernia (CDH) is significantly lower than that of fetuses without any malformations. The objective of this study was to develop and evaluate the first specific sonographic weight formula for fetuses with CDH. In a retrospective, multicenter, cohort study, a statistical estimation technique known as "multivariable fractional polynomial regression" was applied to a group of 146 fetuses with CDH. Each fetus underwent an ultrasound examination with complete biometric parameters within 7 days of delivery. A new formula was derived using the obtained data and was then compared with other commonly used equations. The accuracy of the different formulas was compared using means of signed percentage errors (SPE), medians of absolute percentage errors (MAPE), and fractions of estimates within prespecified error bounds. The new derived formula is: EFW = 10^(4.6729 107 371 + 0.2365 011 768 * HC + 0.2228 897 682 * FL^2 - 0.0129 895 773 * FL^3 - 1.0470 039 072 * (FL * HC)^0.5 + 0.0004 314 661 * (AC * HC) - [in case of liver herniation] 0.0062 112 122), where EFW is the estimated fetal weight, HC is the head circumference, AC is the abdominal circumference, and FL is the femur length. The new formula proved to be superior to other established equations, showing both the lowest median absolute percentage error (MAE: 6.97) and mean signed percentage error (SPE: 0.40), and the best distribution of absolute percentage errors within prespecified error bounds. This new formula significantly improves weight estimation in fetuses with CDH.

Sonographic weight estimation in fetuses with breech presentation

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 7days 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.

Sonographic Weight Estimation in Fetuses with Congenital Diaphragmatic Hernia

To determine the accuracy of sonographic weight estimation (WE) for fetuses with congenital diaphragmatic hernia (CDH), and to assess whether certain sonographic models perform better than others in cases of CDH. In a retrospective, multicenter cohort study, the accuracy of WE in fetuses with CDH (n = 172) was evaluated using eight sonographic models and was compared with a control group of fetuses without malformations (n = 172). Each fetus underwent ultrasound examination with complete biometric parameters within 7 days of delivery. The accuracy of the different formulas was compared using means of percentage errors (MPE), medians of absolute percentage errors (MAPE), and proportions of estimates within 10 % of actual birth weight. Fetuses with CDH had a significantly lower abdominal circumference (AC) in comparison with the control group (293.6 vs. 312.0 mm, p < 0.001). All of the formulas tested in fetuses with CDH, except for the Siemer equation (the only model that does not incorporate any abdominal measurements), showed significantly lower (more negative) MPEs, larger MAPEs, and smaller proportions of estimates within 10 % of actual birth weight in comparison with the control group. The accuracy of sonographic WE in fetuses with CDH is significantly poorer than in fetuses without malformations, principally because of a larger systematic error due to artificially small AC measurements. The development of new, specific models derived from fetuses with CDH could improve the accuracy of WE for infants with this condition.

A New Formula for Optimized Weight Estimation in Extreme Fetal Macrosomia (≥ 4500 g)

To develop and to evaluate a specific sonographic weight formula for fetuses with extreme macrosomia (≥ 4500 g). A statistical estimation technique known as "gradient boosting with component-wise P-splines" was applied to a group of 174 fetuses with a birth weight (BW) ≥ 4500 g. Each fetus underwent an ultrasound examination with complete biometric parameters within 7 days of delivery. The exclusion criteria were multiple pregnancy, intrauterine death, and major structural or chromosomal anomalies. A new formula was derived using the obtained data and was then compared to currently available equations for estimating weight in the macrosomic fetus. The new formula is: log10 (EFW) = 3.6687781710 - 0.0003230278 × (BPD - 100.4080) - 0.0000843433 × (BPD - 100.4080)^2 + 0.0007281281 × (OFD - 120.6322) + 0.0000664323 × (OFD - 120.6322)^2 + 0.000000001794019 × exp(ATD - 120.1552) + 0.0005946974 × (APAD - 121.2069) - 0.0000210137 × (APAD - 121.2069)^2 - 0.000003318 × (APAD - 121.2069)^3, where EFW is the estimated fetal weight, BPD is the biparietal diameter, OFD is the occipitofrontal diameter, ATD is the abdominal transverse diameter, and APAD is the abdominal anteroposterior diameter. The new formula proved to be superior to other established equations, showing the lowest mean absolute percentage error (MAE 2.506), the smallest variance regarding the signed percentage error (SPE) (SD 3.376), and the best distribution of absolute percentage errors within prespecified error bounds. This new formula significantly improves weight estimation in fetuses with extreme macrosomia.

Fetal Weight Estimation in Extreme Macrosomia (≥ 4,500 g): Comparison of 10 Formulas

The aim of this retrospective study was to compare the accuracy of 10 commonly used weight estimation formulas in a group of fetuses with extreme macrosomia ( ≥ 4 ,500 g). Ten formulas were evaluated in a group of 174 fetuses with a birth weight (BW) ≥ 4 ,500 g. Each fetus underwent ultrasound examination with complete biometric parameters within 7 days of delivery. The accuracy of the different formulas for fetal weight estimation (EFW) was compared by mean percentage error (MPE), median of the absolute percentage error (MAPE), the "limits-of-agreement" method and the percentage of EFW falling within the 10 % range of the true birth weight. MPE showed the largest deviation from zero with the Schild formula (MPE - 15.43 %) and the Shepard formula (MPE + 6.08 %) and was closest to zero with the Hadlock II formula (MPE - 5.34 %). The MPE of all formulas showed significant bias when compared to zero. All tested formulas, except the Shepard and Shinozuka equations, significantly underestimated fetal weight. The lowest MAPE was found for the Merz formula (7.23 %). The Hadlock II formula obtained the highest percentage of EWF within the 10 % range of the true birth weight (66.1 %). Exact weight estimation in extreme macrosomia remains an unsolved problem, and can therefore only conditionally provide a sufficient basis for clinical decision processes.

OP12.02: Fetal weight estimation in extreme macrosomia (≥ 4.500 g): comparison of 10 different formulas

Objectives: The aim of this retrospective study was to compare the accuracy of 10 commonly used weight estimation formulas in a group of fetuses with extreme macrosomia (≥4.500 g). Methods: Ten different formulas were evaluated in a group of 174 fetuses with a birth weight (BW) ≥4.500 g. Each fetus underwent ultrasound examination with complete biometric parameters within 7 days of delivery. The accuracy of the different formulas for fetal weight estimation (FWE) was compared by mean percentage error (MPE), median of the absolute percentage error (MAPE), the ‘limitsof-agreement’ method and the percentage of FWE falling within the 10% range of the true birth weight. Results: MPE was largest with the Schild formula (MPE −15.43%) and the Shepard formula (MPE 6.08%) and closest to zero with the Hadlock III formula (MPE 5.34%). The MPE of all formulas showed significant bias when compared to zero. All tested formulas, except the Shepard and Shinozuka equations, significantly underestimated fetal weight. The Hadlock III formula obtained the highest percentage of FWE within the 10% range of the true birth weight (66.3%). However, formulas estimated fetal weight in less than two thirds of cases within the 10% range of the true birth weight. Conclusions: Exact weight estimation in extreme macrosomia remains an unsolved problem questioning clinical decisions solely based on ultrasound data.

OP12.03: The influence of calliper placement on the accuracy of fetal weight estimation in prolonged pregnancies

Objectives: The aim of this retrospective study was to compare the accuracy of 10 commonly used weight estimation formulas in a group of fetuses with extreme macrosomia (≥4.500 g). Methods: Ten different formulas were evaluated in a group of 174 fetuses with a birth weight (BW) ≥4.500 g. Each fetus underwent ultrasound examination with complete biometric parameters within 7 days of delivery. The accuracy of the different formulas for fetal weight estimation (FWE) was compared by mean percentage error (MPE), median of the absolute percentage error (MAPE), the ‘limitsof-agreement’ method and the percentage of FWE falling within the 10% range of the true birth weight. Results: MPE was largest with the Schild formula (MPE −15.43%) and the Shepard formula (MPE 6.08%) and closest to zero with the Hadlock III formula (MPE 5.34%). The MPE of all formulas showed significant bias when compared to zero. All tested formulas, except the Shepard and Shinozuka equations, significantly underestimated fetal weight. The Hadlock III formula obtained the highest percentage of FWE within the 10% range of the true birth weight (66.3%). However, formulas estimated fetal weight in less than two thirds of cases within the 10% range of the true birth weight. Conclusions: Exact weight estimation in extreme macrosomia remains an unsolved problem questioning clinical decisions solely based on ultrasound data.

New Sonographic Method for Fetuses with Small Abdominal Circumference Improves Fetal Weight Estimation

Accurate estimation of fetal weight is a valuable tool for determining further obstetric management. Commonly used weight formulas lack accuracy, even though some equations appear to be favorable within defined weight ranges. However, due to the fact that fetal weight is not known in advance, it is not always clear which formula is suitable. In most of the commonly used equations, the fetal abdominal circumference (AC) is not only included but also has the greatest impact on weight estimation. The aim of our study was to develop and evaluate a new formula specifically designed for a small fetal AC in order to improve weight estimation. The study included 323 pregnancies. The inclusion criteria were singleton pregnancy, ultrasound examination with complete biometric parameters and an AC ≤ 29.0 cm within 7 days of delivery, and an absence of structural or chromosomal malformations. Two "best-fit" formulas were derived by forward regression analysis. Finally, the accuracy of the new formulas was compared to commonly used weight equations by using the percentage error, absolute percentage error (APE), limits of agreement (LOA) and cumulative distribution. Contrary to the routine methods, which significantly underestimated fetal weight, the new formulas did not have a systematic error. The medians of the APE were the lowest (7.13 and 7.16) when compared to other equations. Moreover, the new formulas demonstrated the narrowest LOA. At all discrepancy levels (5%, 10%, 15%, and 20%), the new formulas included significantly more cases than the commonly used methods. The specifically designed equations help to improve fetal weight estimation for fetuses with an AC ≤ 29.0 cm. For optimal weight estimation, we recommend using the new formula II.

New Sonographic Method for Fetuses with a Large Abdominal Circumference Improves Fetal Weight Estimation

Birth weight (BW) is an important prognostic parameter for neonatal morbidity and mortality. Commonly used weight formulas lack accuracy, especially at the lower and upper end of the fetal weight range. Fetal abdominal circumference (AC) as part of most of the commonly used equations has the greatest impact on weight estimation. It has been shown that formulas specifically designed for a small fetal AC can improve weight estimation. The aim was to find out whether a new formula specifically designed for fetuses with a large AC may also improve weight determination. The study included 830 singleton pregnancies. The inclusion criteria were ultrasound examination with complete biometric parameters and an AC ≥36.0cm within 7 days of delivery, and an absence of structural or chromosomal malformations. Two "best-fit" formulas were derived by forward regression analysis. The accuracy of the new formulas was compared with commonly used weight equations using percentage error (PE), absolute percentage error (APE), limits of agreement (LOA) and cumulative distribution. New formula I had no systematic error while new formula II and the routine methods significantly overestimated fetal weight. The medians of the APE were the lowest among the new equations (5.77 and 7.25). The new formulas also demonstrated the narrowest LOA. Importantly, at all discrepancy levels (5%, 10%, 15%, and 20%), new formula I included significantly more cases than the commonly used methods. These specifically designed equations help to improve fetal weight estimation for fetuses with an AC ≥36.0cm. For optimal weight estimation, we recommend using new formula I.

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

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. 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. 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. 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.

OP27.04: New sonographic weight formulae for different ranges of fetal abdominal circumference

Objective: Birth weight is an important predictive parameter for neonatal morbidity and mortality. Accurate estimation of fetal weight is therefore a valuable tool for determining further obstetric management. Commonly used weight formulae have a lack of accuracy. The aim of this study was to develop and to evaluate new formulae specifically designed for different ranges of fetal abdominal circumference (AC). Methods: This study included 5314 pregnancies. Inclusion criteria were singleton pregnancy, ultrasound examination with complete biometric parameters within 7 days before delivery, and absence of structural or chromosomal malformations. With regard to sonographic AC measurements, four subgroups were built (AC: ≤290 mm; AC: 291–330 mm; AC: 331–359 mm; AC: ≥ 360 mm). For each population, best-fit formulae were derived by forward regression analysis with standard biometric measurements as independent variables and birth weight and log(birth weight) as dependent variables, respectively. Finally, accuracy of the new formulae was compared with commonly used weight equations. Results: In all subgroups, except for AC measurements between 331–359 mm, the new weight formulae demonstrated significantly improved accuracy compared to commonly used formulae. Conclusion: Especially in the lower und upper ranges of AC measurements, specifically designed equations help to improve fetal weight estimation.

A New Sonographic Weight Formula for Fetuses ≤ 2500 g

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. 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. 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. With proper application, our new formula can improve the accuracy of fetal weight estimation.

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.

How Good is Fetal Weight Estimation Using Volumetric Methods?

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. 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. 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. 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.

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. For formula finding, 380 preterm singleton pregnancies without fetal anomalies were included. Ultrasound examinations with complete biometric parameters were performed within 7 days before delivery. Stepwise regression analysis was carried out with birth weight as the dependent variable and sonographic parameters (abdominal measurements not included) as independent variables to obtain the best-fit formula. The new equation was evaluated in a group of 97 fetuses with either gastroschisis or omphalocele. In the evaluation group, the mean (SD) percentage error of the new equation was -0.84 (12.03), showing no systematic bias. The mean absolute percentage error was 9.29. The new specific method provided significantly greater accuracy than commonly used formulae. This specific weight formula for fetuses with abdominal wall defects is an accurate method of estimating fetal weight.

Fetal Weight Estimation by Ultrasound: Comparison of 11 Different Formulae and Examiners with Differing Skill Levels

Fetal weight is an important predictive parameter of neonatal morbidity and mortality. Precise estimation of fetal weight is therefore a valuable item of information for further prenatal and obstetric management. Many regression formulae for sonographic fetal weight estimation have been published during the last 30 years, which, unfortunately, generally show poor rates of accuracy. The aim of this study was to compare commonly used formulae in different birth weight groups in order to assess whether any of the formulae are more or less favourable. The second purpose was to estimate the role of examiners on the accuracy of fetal weight estimation. 11 different formulae were evaluated in a group of 1941 pregnancies. Each fetus underwent ultrasound examination with complete biometric parameters within seven days before delivery. The assessment was carried out by either experienced or inexperienced sonographers. Over the whole weight range and in the subgroup of newborns with a birth weight less than 2500 g (n = 160), two Hadlock regression formulae (including abdominal circumference, femur length, head circumference, biparietal diameter, and abdominal circumference, femur length, biparietal diameter, respectively) showed the best levels of accuracy. Infants with a birth weight between 2500 and 3999 g (n = 1570) were best estimated using the gender-specific Schild formula. Macrosomic newborns (n = 211) were best evaluated using Merz's regression formula. The more skilled sonographers were able to achieve much higher intraclass correlation coefficients for all formulae. Some regression formulae appear to be favourable within defined weight ranges. Accuracy of the formulae, however, is still unsatisfactory, and new formulae focusing on specific weight ranges (e. g., macrosomic fetuses) are needed. In addition, experience in obstetric ultrasound improves accuracy of fetal weight estimation.