Fetal weight estimation formulas with head, abdominal, femur, and thigh circumference measurements

Routine third-trimester ultrasound assessment for intrauterine growth restriction

Intrauterine growth restriction significantly impacts perinatal outcomes. Undetected IUGR escalates the risk of adverse outcomes. Serial symphysis-fundal height measurement, a recommended strategy, is insufficient in detecting abnormal fetal growth. Routine third-trimester ultrasounds significantly improve detection rates compared with this approach, but direct high-quality evidence supporting enhanced perinatal outcomes from routine scanning is lacking. In assessing fetal growth, abdominal circumference alone performs comparably to estimated fetal weight. Hadlock formulas demonstrate accurate fetal weight estimation across diverse gestational ages and settings. When choosing growth charts, prescriptive standards (encompassing healthy pregnancies) should be prioritized over descriptive ones. Customized fetal standards may enhance antenatal IUGR detection, but conclusive high-quality evidence is elusive. Emerging observational data suggest that longitudinal fetal growth assessment could predict adverse outcomes better. However, direct randomized trial evidence supporting this remains insufficient.

Development of birth weight estimation model for Ethiopian population from sonographic evaluation

BACKGROUND

Fetal birth weight (FBW) estimation involves predicting the weight of a fetus prior to delivery. This prediction serves as a crucial input for ensuring effective, accurate, and appropriate obstetric planning, management, and decision-making. Typically, there are two methods used to estimate FBW: the clinical method (which involves measuring fundal height and performing abdominal palpation) or sonographic evaluation. The accuracy of clinical method estimation relies heavily on the experience of the clinician. Sonographic evaluation involves utilizing various mathematical models to estimate FBW, primarily relying on fetal biometry. However, these models often demonstrate estimation errors that exceed acceptable levels, which can result in inadequate labor and delivery management planning. One source of this estimation error is sociodemographic variations between population groups in different countries. Additionally, inter- and intra-observer variability during fetal biometry measurement also contributes to errors in FBW estimation.

METHODS

In this research, a novel mathematical model was proposed through multiple regression analysis to predict FBW with an accepted level of estimation error. To develop the model, population data consisting of fetal biometry, fetal ultrasound images, obstetric variables, and maternal sociodemographic factors (age, marital status, ethnicity, educational status, occupational status, income, etc.) of the mother were collected. Two approaches were used to develop the mathematical model. The first method was based on fetal biometry data measured by a physician and the second used fetal biometry data measured using an image processing algorithm. The image processing algorithm comprises preprocessing, segmentation, feature extraction, and fetal biometry measurement.

RESULTS

The model developed using the two approaches were tested to assess their performance in estimating FBW, and they achieved mean percentage errors of 7.53% and 5.89%, respectively. Based on these results, the second model was chosen as the final model.

CONCLUSION

The findings indicate that the developed model can estimate FBW with an acceptable level of error for the Ethiopian population. Furthermore, this model outperforms existing models for FBW estimation. The proposed approach has the potential to reduce infant and maternal mortality rates by providing accurate fetal birth weight estimates for informed obstetric planning.

Role of thigh circumference in predicting the fetal weight: Comparison with other ultrasound methods-A prospective observational study

AIM

We aimed to evaluate the addition of fetal thigh circumference (TC) to other ultrasound parameters to predict fetal weight compared to two standard formulae (Hadlock's and Vintzileos methods).

METHODS

We conducted this prospective study on pregnant women between November 2018 and September 2019. The actual fetal weight was estimated within 48 h of delivery; then, it was compared to the estimated fetal weight by ultrasound. We used the Statistical Package for the Social Sciences (SPSS) software version 20.0 to perform the statistical analysis.

RESULTS

A total of 123 pregnant women, with a mean age of 26.68 (5.24) years and a mean gestational age of 38.78 (0.85) weeks, were included in our study. We detected a significant positive correlation between different ultrasound parameters and actual weight (all p ≤ 0.001). The highest correlation was observed between TC and actual fetal weight (r = 0.685). Regarding both formulae, the correlation coefficient was higher in the Vintzileos formula than the Handlock formula (0.976 vs. 0.823). Our linear regression analysis showed that fetal TC could be an indicator for estimating fetal weight (p < 0.001). There was a statistically significant difference between the actual weight and the weight estimated by the Hadlock formula (p < 0.001). We detected no statistically significant difference between the estimated TC by ultrasound and the actual TC (p = 0.0602).

CONCLUSION

Fetal TC can help accurately measure fetal birth weight when incorporated with other fetal parameters. The inclusion of fetal TC assessment in routine ultrasound examination is suggested to improve the birth estimates.

Sonographic Estimated Fetal Weight Within an Indian Cohort: Is the Hadlock Four Regression Model Appropriate or Does It Merit Adjustments?

Objective:

Sonographic estimated fetal weight (EFW) has an influence on the management of a pregnancy. The Hadlock 4 regression model (Hadlock-4), based on fetal biometry, is widely used. There are significant discrepancies noted between EFW, using Hadlock-4, compared to the actual infant birth weights (ABW) in the author’s clinical practice. The research objective was to compare the EFW, using Hadlock-4, with ABW and determine minor arithmetic modifications needed for this population.

Materials and Methods:

A prospective observational study was done enrolling women in the third trimester, who underwent sonography and delivered within a week of the examination. The sonographic cases were divided into class intervals by gestational age. The EFW were compared with the ABW, using a Pearson coefficient and mean percentage errors (MPE). The EFW values were increased or decreased, by a certain percentage, to keep the mean percentage error in an acceptable range.

Results:

The strength of association between the EFW and ABW was 0.69 ( p = .014). The EFW and the MPEs for women delivering at 36-40 weeks and beyond was significantly more (13.2 and 18.2%). The EFWs at 36-40 weeks and beyond 40 weeks were reduced by 3 and 8% respectively, which reduced the MPEs. After this modification 97.6% of ABWs fell within +/-2 standard deviations of the EFWs.

Conclusion:

A simple 3 and 8% reduction of EFWs, using the Hadlock-4, with those sonographic examinations at 36-40 weeks and beyond 40 weeks gestation respectively, is proposed to increase reliable in this Indian patient practice.

Predicting fetal weight by three-dimensional limb volume ultrasound (AVol/TVol) and abdominal circumference

BACKGROUND

Fetal weight is an important parameter to ensure maternal and child safety. The purpose of this study was to use three-dimensional (3D) limb volume ultrasound combined with fetal abdominal circumference (AC) measurement to establish a model to predict fetal weight and evaluate its efficiency.

METHODS

A total of 211 participants with single pregnancy (28-42 weeks) were selected between September 2017 and December 2018 in the Beijing Obstetrics and Gynecology Hospital of Capital Medical University. The upper arm (AVol)/thigh volume (TVol) of fetuses was measured by the 3D limb volume technique. Fetal AC was measured by two-dimensional ultrasound. Nine cases were excluded due to incomplete information or the interval between examination and delivery >7 days. The enrolled 202 participants were divided into a model group (134 cases, 70%) and a verification group (68 cases, 30%) by mechanical sampling method. The linear relationship between limb volume and fetal weight was evaluated using Pearson Chi-squared test. The prediction model formula was established by multivariate regression with data from the model group. Accuracy of the model formula was evaluated with verification group data and compared with traditional formulas (Hadlock, Lee2009, and INTERGROWTH-21st) by paired t-test and residual analysis. Receiver operating characteristic curves were generated to predict macrosomia.

RESULTS

AC, AVol, and TVol were linearly related to fetal weight. Pearson correlation coefficient was 0.866, 0.862, and 0.910, respectively. The prediction model based on AVol/TVol and AC was established as follows: Y = -481.965 + 12.194TVol + 15.358AVol + 67.998AC, R2adj = 0.868. The scatter plot showed that when birth weight fluctuated by 5% (i.e., 95% to 105%), the difference between the predicted fetal weight by the model and the actual weight was small. A paired t-test showed that there was no significant difference between the predicted fetal weight and the actual birth weight (t = -1.015, P = 0.314). Moreover, the residual analysis showed that the model formula's prediction efficiency was better than the traditional formulas with a mean residual of 35,360.170. The combined model of AVol/TVol and AC was superior to the Lee2009 and INTERGROWTH-21st formulas in the diagnosis of macrosomia. Its predictive sensitivity and specificity were 87.5% and 91.7%, respectively.

CONCLUSION

Fetal weight prediction model established by semi-automatic 3D limb volume combined with AC is of high accuracy, sensitivity, and specificity. The prediction model formula shows higher predictive efficiency, especially for the diagnosis of macrosomia.

TRIAL REGISTRATION

ClinicalTrials.gov, NCT03002246; https://clinicaltrials.gov/ct2/show/NCT03002246?recrs=e&cond=fetal&draw=8&rank=67.

Comparison of sonographic fetal weight estimation formulas in patients with preterm premature rupture of membranes

BACKGROUND

Estimation of fetal weight (EFW) by ultrasound is useful in clinical decision-making. Numerous formulas for EFW have been published but have not been validated in pregnancies complicated by preterm premature rupture of membranes (PPROM). The purpose of this study is to compare the accuracy of EFW formulas in patients with PPROM, and to further evaluate the performance of the most commonly used formula - Hadlock IV.

METHODS

A retrospective cohort study of women with singleton gestations and PPROM, admitted to a single tertiary center between 2005 and 2017 from 22^0/7-33^0/7 (n = 565). All women had an EFW within 14 days of delivery by standard biometry (biparietal diameter, head circumference, abdominal circumference and femur length). The accuracy of previously published 21 estimated EFW formulas was assessed by comparing the Pearson correlation with actual birth weight, and calculating the random error, systematic error, proportion of estimates within 10% of birth weight, and Euclidean distance.

RESULTS

The mean gestational was 26.8 ± 2.4 weeks at admission, and 28.2 ± 2.6 weeks at delivery. Most formulas were strongly correlated with actual birth weight (r > 0.9 for 19/21 formulas). Mean systematic error was - 4.30% and mean random error was 14.5%. The highest performing formula, by the highest proportion of estimates and lowest Euclidean distance was Ott (1986), which uses abdominal and head circumferences, and femur length. However, there were minimal difference with all of the first 10 ranking formulas. The Pearson correlation coefficient for the Hadlock IV formula was strong at r = 0.935 (p < 0.001), with 319 (56.5%) of measurements falling within 10%, 408 (72.2%) within 15% and 455 (80.5%) within 20% of actual birth weight. This correlation was unaffected by gender (r = 0.936 for males, r = 0.932 for females, p < 0.001 for both) or by amniotic fluid level (r = 0.935 for mean vertical pocket < 2 cm, r = 0.943 for mean vertical pocket ≥2 cm, p < 0.001 for both).

CONCLUSIONS

In women with singleton gestation and PPROM, the Ott (1986) formula for EFW was the most accurate, yet all of the top ten ranking formulas performed quite well. The commonly used Hadlock IV performed quite similarly to Ott's formula, and is acceptable to use in this specific setting.

Ensemble Learning to Improve the Prediction of Fetal Macrosomia and Large-for-Gestational Age

Background: The objective of this study was to investigate the use of ensemble methods to improve the prediction of fetal macrosomia and large for gestational age from prenatal ultrasound imaging measurements. Methods: We evaluated and compared the prediction accuracies of nonlinear and quadratic mixed-effects models coupled with 26 different empirical formulas for estimating fetal weights in predicting large fetuses at birth. The data for the investigation were taken from the Successive Small-for-Gestational-Age-Births study. Ensemble methods, a class of machine learning techniques, were used to improve the prediction accuracies by combining the individual models and empirical formulas. Results: The prediction accuracy of individual statistical models and empirical formulas varied considerably in predicting macrosomia but varied less in predicting large for gestational age. Two ensemble methods, voting and stacking, with model selection, can combine the strengths of individual models and formulas and can improve the prediction accuracy. Conclusions: Ensemble learning can improve the prediction of fetal macrosomia and large for gestational age and have the potential to assist obstetricians in clinical decisions.

Birth weight prediction models for the different gestational age stages in a Chinese population

The study aims to develop new birth weight prediction models for different gestational age stages using 2-dimensional (2D) ultrasound measurements in a Chinese population. 2D ultrasound was examined in pregnant women with normal singleton within 3 days prior to delivery (28–42 weeks’ gestation). A total of 19,310 fetuses were included in the study and randomly split into the training group and the validation group. Gestational age was divided into five stages: 28–30, 31–33, 34–36, 37–39 and 40–42 weeks. Multiple linear regression (MLR), fractional polynomial regression (FPR) and volume-based model (VM) were used to develop birth weight prediction model. New staged prediction models (VM for 28–36 weeks, MLR for 37–39 weeks, and FPR for 40–42 weeks) provided lower systematic errors and random errors than previously published models for each gestational age stage in the training group. The similar results were observed in the validation group. Compared to the previously published models, new staged models had the lowest aggregate systematic error (0.31%) and at least a 19.35% decrease; at least a 4.67% decrease for the root-mean-square error (RMSE). The prediction rates within 5% and 10% of birth weight for new staged models were higher than those for previously published models, which were 54.47% and 85.10%, respectively. New staged birth weight prediction models could improve the accuracy of birth weight estimation for different gestational age stages in a Chinese population.

The Accuracy of 22 Fetal Weight Estimation Formulas in Diabetic Pregnancies

PURPOSE

The objective of this study was to estimate the accuracy of 22 fetal weight estimation formulas in diabetic pregnancies uncomplicated and complicated by fetal macrosomia.

METHODS

Retrospectively collected data of 317 pregnancies complicated by gestational diabetes mellitus and 78 cases of fetal macrosomia were used in this study. Study inclusion criteria were women diagnosed with gestational diabetes mellitus, full-term singleton pregnancy, and an interval from the ultrasound to delivery of ≤7 days. The estimated fetal weight was calculated using 22 formulas. The mean absolute percentage error (MAPE) and two-way random interclass correlation coefficient were chosen for statistical analysis.

RESULTS

In the group of gestational diabetes, MAPE ranged from 8.43 ± 10.17 to 54.01 ± 9.50%. Most of the formulas showed a tendency to estimate a lower fetal weight in comparison to the actual birth weight. In the group of fetal macrosomia, the correlations were poor. Only three formulas reached the threshold of MAPE <10%.

CONCLUSIONS

The formula by Hsieh might be considered the best for fetal weight estimation in diabetic pregnancies. The combination of the best formulas might improve the accuracy of estimation. None of the formulas were accurate enough to predict fetal macrosomia.

Ultrasonographic estimation of fetal weight: development of new model and assessment of performance of previous models

OBJECTIVES

To develop a new formula for ultrasonographic estimation of fetal weight and evaluate the accuracy of this and all previous formulae in the prediction of birth weight.

METHODS

The study population consisted of 5163 singleton pregnancies with fetal biometry at 22-43 weeks' gestation and live birth of a phenotypically normal neonate within 2 days of the ultrasound examination. Multivariable fractional polynomial analysis was used to determine the combination of variables that provided the best-fitting models for estimated fetal weight (EFW). A systematic review was also carried out of articles reporting formulae for EFW and comparing EFW to actual birth weight. The accuracy of each model for EFW was assessed by comparing mean percentage error, absolute mean error (AE), proportion of pregnancies with AE ≤ 10% and Euclidean distance.

RESULTS

The most accurate models, with the lowest Euclidean distance and highest proportion of AE ≤ 10%, were provided by the formulae incorporating ≥ 3 rather than < 3 biometrical measurements. The systematic review identified 45 studies describing a total of 70 models for EFW by various combinations of measurements of fetal head circumference (HC), biparietal diameter, femur length (FL) and abdominal circumference (AC). The most accurate model with the lowest Euclidean distance and highest proportion of AE ≤ 10% was provided by the formula of Hadlock et al., published in 1985, which incorporated measurements of HC, AC and FL; there was a highly significant linear association between EFW and birth weight (r = 0.959; P < 0.0001), and EFW was within 10% of birth weight in 80% of cases. The performance of the best model developed in this study, utilizing HC, AC and FL, was very similar to that of Hadlock et al. CONCLUSION: Despite many efforts to develop new models for EFW, the one reported in 1985 by Hadlock et al., from measurements of HC, AC and FL, provides the most accurate prediction of birth weight and can be used for assessment of all babies, including those suspected to be either small or large. Copyright © 2018 ISUOG. Published by John Wiley & Sons Ltd.

Individualized growth assessment: conceptual framework and practical implementation for the evaluation of fetal growth and neonatal growth outcome

Fetal growth abnormalities can pose significant consequences on perinatal morbidity and mortality of nonanomalous fetuses. The most widely accepted definition of fetal growth restriction is an estimated fetal weight less than the 10th percentile for gestational age according to population-based criteria. However, these criteria do not account for the growth potential of an individual fetus, nor do they effectively separate constitutionally small fetuses from ones that are malnourished. Furthermore, conventional approaches typically evaluate estimated fetal weight at a single time point, rather than using serial scans, to evaluate growth. This article provides a conceptual framework for the individualized growth assessment of a fetus/neonate based on measuring second-trimester growth velocity of fetal size parameters to estimate growth potential. These estimates specify size models that generate individualized third-trimester size trajectories and predict birth characteristics. Comparisons of measured and predicted values are used to separate normally growing fetuses from those with growth abnormalities. This can be accomplished with individual anatomical parameters or sets of parameters. A practical and freely available software (Individualized Growth Assessment Program) has been developed to allow implementation of this approach for clinical and research purposes.

Different formulas, different thresholds and different performance-the prediction of macrosomia by ultrasound

OBJECTIVE

The sonographic prediction of fetal macrosomia affects obstetrical decision regarding the timing and mode of delivery. We aimed to compare the accuracy of various formulas for prediction of macrosomia at different thresholds.

STUDY DESIGN

This was a retrospective cohort study of singleton gestations at term, with fetal biometrical measurements taken up to 7 days prior to delivery (2007 to 2014). Sonographic estimated fetal weight was calculated using 20 previously published formulas. Macrosomia prediction was evaluated for every formula utilizing: (1) measures of accuracy (sensitivity, specificity and so on); (2) comparison of the systematic and random errors (SE and RE), and the proportion of estimates within 10% of actual birth weight for macrosomic and non-macrosomic neonates. Performance measurements were evaluated for different macrosomia thresholds: 4000, 4250 and 4500 g. Best performing formula for every threshold was defined as the one with the lowest Euclidean distance (=SQRT(SE²+RE²)).

RESULTS

Out of 7977 women who met the inclusion criteria, 754 (9.4%) delivered a neonate weighing ⩾4000 g, 266 (3.3%) delivered a neonate weighing⩾4250 g and 75 (0.9%) delivered a neonate weighing⩾4500 g. Considerable variability was noted between the accuracy parameters of the different formulas, with Woo's formula integrating Abdominal circumference (AC) and femur length (FL) as the most sensitive formula with the highest negative predictive value for all thresholds and Woo's formula using AC, FL and biparietal diameter (BPD) as the most specific for all thresholds. The same formula also demonstrated the best overall accuracy. Regardless of threshold chosen, 80% or more of formulas demonstrated negative systematic error, meaning lower EFW than actual birthweight. As for the Euclidean distance, Hadlock's formula (AC, FL and BPD) ranked the highest for the 4000 and 4250 g thresholds, whereas Shepard's formula (AC and BPD) ranked the highest for the 4500 g threshold.

CONCLUSION

Considerable variability exist between formulas for prediction of neonatal macrosomia. Formulas by Hadlock's and Shepard's utilizing AC, BPD±FL were most accurate for macrosomia prediction at 4000, 4250 and 4500 g thresholds, respectively.

Prediction of large for gestational age by various sonographic fetal weight estimation formulas-which should we use?

OBJECTIVE

As sonographic estimation of fetal weight (EFW) carries substantial impact, especially in large-for-gestational-age (LGA) neonates, we aimed to compare the accuracy of various formulas for prediction of LGA neonates.

STUDY DESIGN

Retrospective cohort study of singleton gestations at term, with EFW up to 7 days before delivery (2007 to 2014). Small-for-gestational-age neonates were excluded. LGA prediction for various formulas was evaluated by: (i) measures of performance (sensitivity, specificity, etc.); (ii) systematic and random errors (SE and RE) and the proportion of estimates (POEs) exceeding 10% of actual birth weight. Best performing formula was defined as the one with the lowest Euclidean distance [=square root of (SE²+RE²)].

RESULTS

Out of 62 102 deliveries, 7996 met inclusion criteria, of which 1618 neonates were LGA (22%). There was a considerable variation in sensitivity (74.6±16.3%, 23.5% to 99%), specificity (86.3±10.6%, 51.7% to 99.6%), positive predictive value (64.9±12.4%, 35.6% to 93.8%), positive likelihood ratio (LR; 9.3±10.9, 2.1 to 54.2) and negative LR (0.3±0.16, 0.02 to 0.8), a mild variation in the negative predictive value (92.9±3.7%, 82.3% to 99.5%) and a minimal variation in the area under the curve (94.3%, 93.0 to 95.1; mean±s.d., range for all). Absolute SE was higher for the LGA group in 11/20 formulas (55%). The RE and POE were lower in 19/20 (95%) and 14/20 (70%) for the LGA neonates, respectively.

CONCLUSION

There is a wide variation in EFW formulas performance for detecting LGA. Hadlock's formula (1985) combining abdominal circumference, femur length and biparietal diameter ranked highest.

Effect of fetal presentation on sonographic estimation of fetal weight according to different formulas

OBJECTIVE

To compare the accuracy of various sonographic estimation of fetal weight (sEFW) formulas for breech-presenting fetuses.

METHODS

A retrospective analysis of sEFW performed within 3 days of delivery in a tertiary medical center in Israel between July 2007 and December 2014 was conducted. Breech-presenting singleton fetuses were matched by sex and birth weight to vertex-presenting fetuses. sEFW was calculated using 21 formulas. Systematic and random errors, proportion of estimates (POE) within 10% of actual birth weight, and reliability analysis were used to compare sonographic accuracy. The best performing formula was determined by Euclidean distance.

RESULTS

Both groups contained 274 fetuses. Systematic error was lower for breech fetuses when compared with control fetuses in 17 of 21 formulas; there was no significant difference in random error between the breech and vertex groups. For vertex fetuses, Euclidean distance was smaller in 17 of 21 formulas, and POE within 10% of birth weight was higher in most formulas. Cronbach α value was higher for vertex fetuses than for breech fetuses in all formulas. The formulas of Combs et al. and Hadlock et al. were highest ranking for breech-presenting fetuses.

CONCLUSION

sEFW might be more accurate for vertex than for breech fetuses.

Estimation of fetal weight by ultrasonography after preterm premature rupture of membranes: comparison of different formulas

OBJECTIVE

To compare different ultrasonographic fetal weight estimation formulas in predicting the fetal birth weight of preterm premature rupture of membrane (PPROM) fetuses.

METHODS

Based on the ultrasonographic measurements, the estimated fetal weight (EFW) was calculated according to the published formulas. The comparisons used estimated birth weight (EBW) and observed birth weight (OBW) to calculate the mean absolute percentage error [(EBW-OBW)/OBW×100], mean percentage error [(EBW-OBW)/OBW×100)] and their 95% confidence intervals.

RESULTS

There were 234 PPROM patients in the study period. The mean gestational age at which PPROM occured was 31.2±3.7 weeks and the mean gestational age of delivery was 32.4±3.2 weeks. The mean birth weight was 1892±610 g. The median absolute percentage error for 33 formulas was 11.7%. 87.9% and 21.2% of the formulas yielded inaccurate results when the cut-off values for median absolute percentage error were 10% and 15%, respectively. The Vintzileos' formula was the only method which had less than or equal to 10% absolute percentage error in all age and weight groups.

CONCLUSIONS

For PPROM patients, most of the formulas designed for sonographic fetal weight estimation had acceptable performance. The Vintzileos' method was the only formula having less than 10% absolute percentage error in all gestational age and weight groups; therefore, it may be the preferred method in this cohort. Amniotic fluid index (AFI) before delivery had no impact on the performance of the formulas in terms of mean percentage errors.

Ultrasonography-based Fetal Weight Estimation: Finding an Appropriate Model for an Indian Population

Background:

Very limited information is available regarding the accuracy and applicability of various ultrasonography parameters [abdominal circumference (AC), biparietal diameter (BPD), femur length (FL), and head circumference (HC)]-based fetal weight estimation models for Indian population. The objective of this study was to systematically evaluate commonly used fetal weight estimation models to determine their appropriateness for an Indian population.

Methods:

Retrospective data of 300 pregnant women was collected from a tertiary care center in Bengaluru, India. The inclusion criteria were a live singleton pregnancy, gestational age ≥ 34 weeks, and last ultrasound scan to delivery duration ≤ 7 days. Cases with suspected fetal growth restriction or malformation were excluded. For each case, fetal weight was estimated using 34 different models. The models specifically designed for low birth weight, small for gestation age, or macrosomic babies were excluded. The models were ranked based on their mean percentage error (MPE) and its standard deviation (random error). A model with the least MPE and random error ranking was considered as the best model.

Results:

In total, 149 cases were found suitable for the study. Out of 34, only 12 models had MPE within ± 10% and only seven models had random error < 10%. Most of the Western population-based models had a tendency to overestimate the fetal weight. Based on MPE and random error ranking, the Woo’s (AC-BPD) model was found to be the best, followed by Jordaan (AC), Combs (AC-HC-FL), Hadlock (AC-HC), and Hadlock-3 (AC-HC-FL) models. It was observed that the models based on just AC and AC-BPD combinations had statistically significant lesser MPE than the models based on all other combinations (p < 0.05).

Conclusion:

It was observed that the existing models have higher errors on Indian population than on their native populations. This points toward limitations in direct application of these models on Indian population without due consideration. Therefore, it is recommended that clinicians should exert caution in interpretation of fetal weight estimations based on these models. Moreover, this study highlights a need of models based on native Indian population.

A new mathematical formula to predict the foetal weight in twin pregnancies: A comparison of it with 19 different formulas

One hundred and seventy-two twin-pregnant patients were enrolled. The estimated foetal weight was calculated using 19 different formulas. Ong's formula (0.954 (95%CI = 0.938/0.966)), which was designed specifically for twins, produced the highest Cronbach's alpha value followed by Hadlock II (0.952 (95%CI = 0.935/0.965)), Hadlock I (0.952 (95%CI = 0.935/0.964)), Hadlock III (0.952 (95%CI = 0.935/0.964)), Hadlock IV (0.952 (95%CI = 0.935/0.964)) and our formula (0.952 (95%CI = 0.935/0.964)), which produced the same Cronbach's alpha values for twin A. For twin B, our formula produced the highest Cronbach's alpha value (0.961 (95%CI = 0.948/0.972) followed by Hadlock II (0.960 (95%CI = 0.946/0.971)), Hadlock I (0.960 (95%CI = 0.946/0.970)), Hadlock III (0.960 (95%CI = 0.946/0.970)) and Hadlock IV (0.960 (95%CI = 0.946/0.970)). In conclusion, our formula (AC, FL) performed well in predicting the foetal weights in twin pregnancies (>24 weeks) in our study. However, it should be tested in other populations. Hadlock II (AC, FL) produced a comparable performance to Hadlock I (BPD, HC, AC, FL), Hadlock III (BPD, AC, FL) and Hadlock IV (HC, AC, FL). Hadlock II may be preferable in twin pregnancies since it is based on AC and FL only.

Comparison of Errors of 35 Weight Estimation Formulae in a Standard Collective

Issue: The estimation of foetal weight is an integral part of prenatal care and obstetric routine. In spite of its known susceptibility to errors in cases of underweight or overweight babies, important obstetric decisions depend on it. In the present contribution we have examined the accuracy and error distribution of 35 weight estimation formulae within the normal weight range of 2500-4000 g. The aim of the study was to identify the weight estimation formulae with the best possible correspondence to the requirements of clinical routine. Materials and Methods: 35 clinically established weight estimation formulae were analysed in 3416 foetuses with weights between 2500 and 4000 g. For this we determined and compared the mean percentage error (MPE), the mean absolute percentage error (MAPE), and the proportions of estimates within the error ranges of 5, 10, 20 and 30 %. In addition, separate regression lines were calculated for the relationship between estimated and actual birth weights for the weight range 2500-4000 g. The formulae were thus examined for possible inhomogeneities. Results: The lowest MPE were achieved with the Hadlock III and V formulae (0.8 %, STW 9.2 % or, respectively, -0.8 %, STW 10.0 %). The lowest absolute error (6.6 %) as well as the most favourable frequency distribution in cases below 5 % and 10 % error (43.9 and 77.5) were seen for the Halaska formula. In graphic representations of the regression lines, 16 formulae revealed a weight overestimation in the lower weight range and an underestimation in the upper range. 14 formulae gave underestimations and merely 5 gave overestimations over the entire tested weight range. Conclusion: The majority of the tested formulae gave underestimations of the actual birth weight over the entire weight range or at least in the upper weight range. This result supports the current strategy of a two-stage weight estimation in which a formula is first chosen after a pre-estimation of the weight range.

Prediction of Small for Gestational Age: Accuracy of Different Sonographic Fetal Weight Estimation Formulas

Objective: To compare the accuracy of various sonographic estimated fetal weight (sEFW) formulas for the prediction of small for gestational age (SGA) neonates. Methods: A retrospective analysis of 6,126 fetal biometrical measurements performed within 3 days of delivery. SGA prediction was evaluated for various sEFW formulas by calculating the sensitivity, specificity, positive/negative predictive value (PPV/NPV), likelihood ratio (+LR/-LR), overall accuracy and area under the receiver operating characteristic curve (AUC). Systematic error, random error, proportion of estimates >10% of birth weights, actual and absolute weight differences were compared between SGA and non-SGA neonates. Results: Overall, 638 (10.4%) neonates were SGA. There was considerable variation among formulas in sensitivity (mean ± SD, 62 ± 14.4%; range, 32.4-91.2), PPV (72.5 ± 10.7%; 45.8-95.6) and +LR (24.2 ± 10.9; 7.2-57.3), mild variation in specificity (96.6 ± 2.7%; 87.4-99.4), NPV (94.6 ± 5.3%; 72.2-98.9) and -LR (0.4 ± 0.1; 0.1-0.7) and minimal variation in AUC (mean, 0.93; range, 0.91-0.93). The majority of formulas had a lower accuracy for the SGA neonates, with systematic error and random error ranging from -4.2 to 14.3% and from 8.4 to 12.9% for SGA, and from -8.7 to 16.1% and from 7.2 to 10.5% for non-SGA, respectively. Conclusion: sEFW formulas differ in their accuracy for SGA prediction. In our population, the most accurate formula for SGA prediction was Hadlock's formula utilizing femur length, abdominal and head circumference.

Hepato - Cephalic Index as a Predictor of Intrauterine Growth Restriction

Aim:

The aims of this study were to compare ultrasound fetoplacental parameters and to calculate Hepato-Cephalic Index (HCI) as a new predictor of IUGR.

Methods and material:

A clinical prospective study was conducted and included 120 pregnant women divided in two groups: non IUGR group included healthy pregnant women (n=60) and IUGR group included pregnant women with preeclampsia and IUGR (n=60). Outcome measures were following ultrasound fetoplacental parameters in fetuses with IUGR and non IUGR: Fetal Liver Length (FLL), Femur Length (FL), Biparietal Diameter (BPD), Placental Maturation by Grannum, Amniotic Fluid Index (AFI) and Hepato-Cephalic Index (HCI). Sonography was carried out by probe 3.5 Mhz type MINDRAY DC 7.

Results:

The mean of maternal age was 30.0±6.1 years in women with preeclampsia and IUGR and 28.1±5.1 years in healthy pregnant women, p > 0.05. There was a statistically significant difference in values of: FLL (p < 0.001), FL (p = 0.004), BPD (p < 0.001), AFI (p < 0.001), HCI (p < 0.001) between IUGR and non IUGR groups. The most of women with preeclampsia and IUGR had grade III of placental maturation (48.3%). There is a significant association between the placental maturation and the diagnosis, p < 0.001. There was a statistically significant difference in body mass of newborns between IUGR and non IUGR groups, p < 0.001.

Conclusion:

In a fetus with IUGR in preeclampsia there is a reduction in FLL, FL, BPD, AFI and HCI and there is a early maturation of the placenta. By measurement of fetoplacental ultrasonic parameters of liver, pregnant women will experience prediction of risk pregnancy (preeclampsia with IUGR) due to hypoxia.

Choice of Formula and Accuracy of Fetal Weight Estimation in Small-for-Gestational-Age Fetuses

OBJECTIVES

The purpose of this study was to identify the most accurate sonographic models for fetal weight estimation in specific subgroups of small-for-gestational-age (SGA) fetuses.

METHODS

We conducted a retrospective study of women who delivered an SGA neonate and underwent a sonographic estimation of fetal weight within 7 days of delivery in a single tertiary center (n = 370). The accuracy of fetal weight estimation was compared for 33 sonographic models (27 nontargeted and 6 targeted SGA- or low-birth-weight-specific models) in specific subgroups of SGA fetuses: early versus late SGA, asymmetric versus symmetric, and presence of Doppler abnormalities.

RESULTS

A wide variation in the accuracy of the different models was found (systematic error, -12.5% to 15.1%; random error, 7.8% to 15.5%). Most nontargeted models tended to systematically overestimate the weight of SGA fetuses. The best performing model in the overall SGA group was the targeted model of Scott et al (J Ultrasound Med 1996; 15:669-672; systematic error ± random error, -2.8% ± 8.3%). However, the optimal models varied for different subgroups of SGA fetuses, and in most cases the targeted models were the most accurate. An approach that used the optimal model for each subgroup of SGA fetuses compared with the uniform use of the model of Scott et al for all SGA fetuses was associated with a lower systematic error (-0.38% versus -2.8%; P < .001) and a higher proportion of weight estimations within 5%, 10%, and 15% of birth weight (48.4% versus 40.8%; P= .038; 78.6% versus 71.4%; P= .022; 95.1% versus 89.2%; P = .003, respectively).

CONCLUSIONS

Sonographic models in current use for fetal weight estimation in SGA fetuses have significant errors, and their performance varies for specific subgroups of SGA fetuses. An approach that uses subgroup-specific models may improve the accuracy of weight estimation among SGA fetuses.

Ultrasound (in)accuracy: it's in the formulae not in the technique - assessment of accuracy of abdominal circumference measurement in term pregnancies

Introduction: Fetal abdominal circumference (AC) is utilised in calculations for the estimation of fetal weight (EFW) and has been proposed as a method of monitoring diabetic pregnancies. We evaluated true ultrasound accuracy by comparing fetal AC biometry with neonatal anthropometry and compared this with standard ultrasound estimations of fetal weight.

Methods: A prospective observational study was performed at a tertiary referral centre. Women who were having their confinement of a term, singleton gestation either by induction of labour or elective caesarean section from 2009–2011 were approached to participate. An ultrasound was performed within 24 hours of delivery measuring the biometric parameters of AC, head circumference (HC), biparietal diameter and femur length. Following delivery the AC, HC and birthweight were measured on the neonate.

Results: Fifty‐two patients were enrolled in the study with data collected from 50. Mean AC measurement was 35.1 ± 2.1 cm and birth weight was 3596 ± 517 g. A Bland‐Altman plot was used to compare the two AC measurements with the 95% limits of agreement ranging from −2.33–4.69 cm around a mean difference of 1.2 cm. Mean percentage error was 5.0% and 6.2% for the AC and HC measurements respectively, in comparison with percentage errors of 7.0–13.8% for estimation of fetal weight (EFW) from 27 formulae.

Conclusions: Sonographic AC measurement is accurate in term pregnancies, with a percentage error less than HC or EFW. Perceptions of ultrasound inaccuracy may relate to the application of formulae rather than the ultrasound technique itself. Fetal surveillance using serial AC measurement has been proposed, in particular monitoring of diabetic pregnancies and in such a group AC may be easier and faster to obtain and more meaningful than EFW.

Role of ultrasound in the management of diabetes in pregnancy

The purpose of this review is to discuss the established role of ultrasound (US) in the management of pregnancy complicated by diabetes mellitus (DM), as well as new developments with regard to the use of US in this situation. We choose to explore the role of US in pregnancy complicated by DM in three areas: (1) Role of US in estimation of fetal weight. (2) Role of US in diagnosis of congenital malformation. (3) Role of US in monitoring diabetic pregnant patients.

A search for the most accurate formula for sonographic weight estimation by fetal sex - a retrospective cohort study

OBJECTIVE

The aim of this study was to assess the effect of fetal sex on the accuracy of multiple formulas for sonographic estimation fetal weight (SEFW).

METHODS

The cohort included all singleton live births recorded at a single medical center from January 2004 to September 2011. The accuracy of SEFW was compared between male and female fetuses using 6575 SEFW performed within 3 days prior to delivery. Fetal weight was estimated using 27 models.

RESULTS

The accuracy of different formulas in predicting birth weight of male and female fetuses was found to be significantly different in almost every accuracy index that was compared (P < 0.05). The model by Sabbagha et al. was found to be the most accurate in assessing female fetuses. The most accurate model for male fetuses was a sex-specific formula by Melamed et al. We also found that a combination of the most accurate formula for each sex to one combined sex-specific model increased SEFW accuracy significantly.

CONCLUSION

The accuracy of SEFW is significantly related to fetal sex. The combination of the formulas by Melamed et al. and Sabbagha et al. for male and female fetuses accordingly allowed more accurate SEFW in our research population.

Ultrasound estimation of birth weight in twin pregnancy: comparison of biometry algorithms in the STORK multiple pregnancy cohort

OBJECTIVES

The aims of this study were first, to ascertain the accuracy of formulae for ultrasonographic birth-weight estimation in twin compared with singleton pregnancies and second, to assess the accuracy of sonographic examination in the prediction of birth-weight discordance in twin pregnancies.

METHODS

This was a retrospective cohort study including both singleton and twin pregnancies. Routine biometry was recorded and estimated fetal weight (EFW) calculated using 33 different formulae. Only pregnancies that delivered within 48 h of the ultrasound scan were included (4280 singleton and 586 twin fetuses). Differences between the EFW and actual birth weight (ABW) were assessed by percentage error, accuracy in predictions within ± 10% and ± 15% of error and use of the Bland-Altman method. The accuracy of prediction of the different cut-offs of birth-weight discordance in twin pregnancies was also assessed using the area under the receiver-operating characteristics curve (AUC).

RESULTS

The overall mean absolute percentage error was ≤ 10% for 25 formulae in singleton pregnancies compared with three formulae in twin pregnancies. The overall predictions within ± 10% and ± 15% of the ABW were 62.2% and 81.5% in singleton and 49.7% and 68.5% in twin pregnancies, respectively. When t e formulae were categorized according to the biometric parameters included, those based on a combination of head, abdomen and femur measurements showed the lowest mean absolute percentage error, in both singleton and twin pregnancies. The predictive accuracy for 25% birth-weight discordance using the Hadlock 2 formula, as assessed by the AUC, was 0.87.

CONCLUSIONS

Ultrasound estimation of birth weight is less accurate in twin than in singleton pregnancies. Formulae that include a combination of head, abdomen and femur measurements perform best in both singleton and twin pregnancies.

Estimation of mouse fetal weight by ultrasonography: application from clinic to laboratory

Ultrasonographic assessment of fetal growth to estimate fetal weight has been widely used in clinical obstetrics but not in laboratory mice. Even though it is important to assess fetal growth abnormalities for gene-targeting studies using mice, there have been no reports of accurately estimated fetal weight using fetal biometric parameters in mice. The aim of this study was to establish an accurate mouse formula using fetal biometric parameters under ultrasound imaging. Using a high-frequency ultrasound system with a 40 MHz transducer, we measured 293 fetuses of biparietal diameter and mean abdominal diameter from day 12.5 postcoitus (p.c.) until day 18.5 p.c every day. Thirteen algorithms for humans based on head and/or abdominal measurements were assessed. We established an accurate formula based on measurement of the abdomen in Jcl:ICR mice to investigate gestational complications, such as intrauterine growth restriction.

Birth-weight prediction using three-dimensional sonographic fractional thigh volume at term in a Chinese population

OBJECTIVES

To develop and validate new birth-weight prediction models in Chinese pregnant women using fractional thigh volume.

METHODS

Healthy late third-trimester fetuses within 5 days of delivery were prospectively examined using two- (2D) and three- (3D) dimensional ultrasonography. Measurements were performed using 2D ultrasound for standard fetal biometry and 3D ultrasound for fractional thigh volume (TVol) and middle thigh circumference. The intraclass correlation coefficient (ICC) was used to analyze the inter- and intraobserver reliability of the 3D ultrasound measurements of 40 fetuses. Five birth-weight prediction models were developed using linear regression analysis, and these were compared with previously published models in a validation group.

RESULTS

Of the 290 fetuses studied, 100 were used in the development of prediction models and 190 in the validation of prediction models. The inter- and intraobserver variability for TVol and middle thigh circumference measurements was small (all ICCs ≥ 0.95). The prediction model using TVol, femur length (FL), abdominal circumference (AC) and biparietal diameter (BPD) provided the most precise birth-weight estimation, with a random error of 4.68% and R(2) of 0.825. It correctly predicted 69.5 and 95.3% of birth weights to within 5 and 10% of actual birth weight. By comparison, the Hadlock model with standard fetal biometry (BPD, head circumference, AC and FL) gave a random error of 6.41%. The percentage of birth-weight prediction within 5 and 10% of actual birth weight was 46.3 and 82.6%, respectively.

CONCLUSION

Consistent with studies on Caucasian populations, a new birth-weight prediction model based on fractional thigh volume, BPD, AC and FL, is reliable during the late third trimester in a Chinese population, and allows better prediction than does the Hadlock model.

Prediction of fetal macrosomia: effect of sonographic fetal weight-estimation model and threshold used

OBJECTIVE

To compare the accuracy of 21 sonographic fetal weight-estimation models and abdominal circumference (AC) as a single measure for the prediction of fetal macrosomia (> 4000 g) using either fixed or optimal model-specific thresholds.

METHODS

A total of 4765 sonographic weight estimations performed within 3 days prior to delivery were analyzed. The predictive accuracy of 21 published sonographic fetal weight-estimation models was calculated using three different thresholds: a fixed threshold of 4000 g; a model-specific threshold obtained from the inflexion point of the receiver-operating characteristics (ROC) curve; and a model-specific threshold associated with the highest overall accuracy. Cluster analysis was used to determine whether a certain combination of fetal biometric indices is associated with a higher predictive accuracy than others.

RESULTS

For a fixed threshold of > 4000 g, there was considerable variation among the models in sensitivity (range, 13.6-98.5%) and specificity (range, 63.6-99.8%) for fetal macrosomia. Use of the threshold derived from the inflexion point of the ROC curve decreased the intermodel variation to a minimum (sensitivity, 84.4-91.4%; and specificity, 79.5-86.3%). Even when this optimal model-specific threshold was applied, models based on three to four biometric indices were more accurate than were models based on only two biometric indices or on AC as a single measure (P=0.03).

CONCLUSIONS

Sonographic fetal weight-estimation models based on three to four biometric indices appear to be more accurate than are models based on two indices or on AC as a single measure, for the diagnosis of macrosomia. In these cases, the use of an optimal, model-specific threshold is associated with a higher degree of accuracy than is the uniform use of a fixed threshold of an estimated weight of > 4000 g.

Reprodutibilidade do volume de membros fetais pela ultrassonografia tridimensional utilizando o método XI VOCAL

OBJETIVO: Avaliar a reprodutibilidade do volume do braço e coxa fetais aferido pela ultrassonografia tridimensional utilizando o método eXtended Imaging Virtual Organ Computer-aided AnaLysis (XI VOCAL). MATERIAIS E MÉTODOS: Realizou-se estudo de reprodutibilidade com 43 fetos normais entre 20 e 37 semanas. Para o cálculo do volume do braço e coxa fetais utilizou-se o método XI VOCAL com delimitação de 10 planos consecutivos. Para o cálculo da variabilidade interobservador, um examinador realizou uma medida do volume do braço e coxa dos 43 fetos, enquanto um segundo examinador, sem o conhecimento prévio dos resultados do primeiro examinador, realizou uma segunda medida dos mesmos volumes. Utilizaram-se, para os cálculos estatísticos, o coeficiente de correlação intraclasse (ricc), gráficos de Bland-Altman e teste t-Student pareado (p). RESULTADOS: Observou-se alta reprodutibilidade interobservador. Para o volume do braço, obtiveram-se ricc = 0,996 (intervalo de confiança [IC] 95%: 0,992; 0,998) e média das diferenças = 0,13 ± 1,29% (95% limites de concordância: -2,54; +2,54%). Para o volume da coxa, obtiveram-se ricc = 0,997 (IC 95%: 0,995; 0,999) e média das diferenças = 0,24 ± 7,60% (95% limites de concordância: -7,6; +7,6%). CONCLUSÃO: O volume do braço e coxa fetais aferido pela ultrassonografia tridimensional utilizando o método XI VOCAL apresentou elevada reprodutibilidade interobservador.

Approach for estimating fetal body weight using two-dimensional ultrasound

OBJECTIVE

Estimation of fetal weight is essential in daily obstetric clinical practice. Most formulas for the estimation involve head measurement. However, predicting fetal weight by head measurement is virtually impossible when the fetal head is positioned low in the pelvic cavity. A convenient method for estimating fetal body weight without head measurement is therefore required.

METHODS

Women who delivered between August 2001 and June 2002 in our center were the subjects of the present study. All infants were delivered within 48 h of an ultrasound examination. Only thigh measurements were made in an attempt to obtain an estimation formula by conventional two-dimensional ultrasonography in 83 patients. As a parameter, femur length (FL) and the largest cross-sectional area at right angles to the long axis of the thigh were used. The derived formula was compared with an established equation in 58 parturients.

RESULTS

The FL value multiplied by the square root of the cross-sectional area of the thigh showed a significant correlation with the actual birth weight. A formula with only two parameters (FL and cross-sectional area of the thigh) was found by linear regression.

CONCLUSION

The formula derived using only thigh measurements was found to be convenient among all the established formulas for estimated fetal body weight, and no head measurement was necessary.

Is sonographic assessment of fetal weight influenced by formula selection?

OBJECTIVE

Several published formulas exist for the determination of estimated fetal weight (EFW), with limited data on their comparative accuracies. The aims of our study were to assess and compare the performance of different EFW formulas in predicting actual birth weight (BW) in an urban population.

METHODS

Patients with an EFW determined within 7 days of delivery were considered eligible for the study. Fourteen published formulas, derived from populations comparable to ours, were used to recalculate EFWs from the same initial measurements. The accuracy of the EFWs obtained from the different formulas were compared by percentage error methods using bias and precision and Bland-Altman limits of agreement methods. Sensitivity and specificity for prediction of being small for gestational age (SGA) were calculated.

RESULTS

Eighty-one fetuses were included in the study. Formula C of Hadlock et al [Hadlock C; log(10) BW = 1.335 - 0.0034(abdominal circumference [AC])(femur length [FL]) + 0.0316(biparietal diameter) + 0.0457(AC) + 0.1623(FL); Am J Obstet Gynecol 1985; 151:333-337] had the best performance according to the bias and precision method. Bland-Altman limits of agreement confirmed these results. Among the formulas, the sensitivity for detection of SGA ranged from 72% to 100%, and specificity was 41% to 88%. Hadlock C had the optimal sensitivity/specificity trade-off for detection of SGA.

CONCLUSIONS

Fourteen formulas showed considerable variation of bias and precision in our population as well as a wide range of sensitivities and specificities for SGA. The choice of the appropriate formula for EFW in a given population should be based on objective and explicit criteria. Consideration of bias and precision for the formula in the population being assessed is critical and may affect clinical care.

A review of sonographic estimate of fetal weight: Vagaries of accuracy

PURPOSE

To determine the factors that might influence the accuracy of sonographic estimated fetal weight.

STUDY DESIGN

A PubMed search (Jan 1975 to Jan 2003) of articles published in the English language was carried out and the inclusion criterion was that estimates were within 10% of birth weight. A Chi-square test for trend was used and odds ratio (OR) with 95% confidence intervals (CI) was calculated.

RESULTS

Over 28 years, 175 articles were identified but only 54 (31%) met the inclusion criterion. Overall 62% (8895/14 384) of the predictions were within 10% of the actual weight. The accuracy was significantly different in articles where <7 vs. >7 days were allowed to lapse between examination and delivery (OR 2.17, 95% CI 1.93, 2.45); where examinations were done by registered diagnostic medical sonographers (RDMS; 65%) versus physicians (59%) or residents (57%; p < 0.0001); in term vs. preterm patients (OR 1.97, 95% CI 1.67, 2.13); and in studies with >1000 vs. <1000 cohorts (OR 1.62; 95% CI 1.51, 1.74).

CONCLUSIONS

If feasible the sonographic examination should be done by RDMS and within a week of delivery.

Sonographic fetal weight estimation: which model should be used?

OBJECTIVE

The purpose of this study was to compare the accuracy of different sonographic models for fetal weight estimation.

METHODS

We evaluated 26 different models using 3705 sonographic weight estimations performed less than 3 days before delivery. Models were ranked on the basis of systematic and random errors and were grouped according to the combination of biometric indices in each model. Cluster analysis was used to compare the accuracy of the different model groups.

RESULTS

A considerable variation in the accuracy of the different models was found. For birth weights (BWs) in the range of 1000 to 4500 g, models based on 3 or 4 fetal biometric indices were significantly more accurate than models that incorporated only 1 or 2 indices. The accuracy of weight estimation decreased at the extremes of BWs, leading to overestimation in low-BW categories as opposed to underestimation when the BW exceeded 4000 g. The precision of most models was lowest in the low-BW groups.

CONCLUSIONS

To improve the accuracy of fetal weight estimation, sonographic models that are based on 3 or 4 fetal biometric indices should be preferred. Recognizing the accuracy and the tendency for underestimation or overestimation of each of the available models is important for the judicious interpretation of fetal weight estimations, especially at the extremes of fetal weight.

New regression formulas for sonographic weight estimation within 10, 7, and 3 days of delivery

OBJECTIVES

The purpose of this study was to develop new regression formulas based on large numbers of sonographic examinations performed within 10, 7, and 3 days of delivery.

METHODS

Sonographic fetal biometric measurements and delivery ward data for an unselected population were analyzed. Multivariate linear regression models were fitted to the sonographic data to predict the actual birth weight (BW) within 10, 7, and 3 days.

RESULTS

The analyses included 6289, 5449, and 4007 patients who underwent sonographic examinations within 10, 7, and 3 days of delivery, respectively. All models yielded very high correlation coefficients (r = 0.927-0.958; R(2) = 0.859-0.918), low mean deviations between the calculated and actual BWs (6.4%-6.6% +/- 1 SD of 5.5%-5.9%), and high percentages of the calculated BW within 10% of the actual BW (78.5%-80.4%). Estimated fetal weight analyses made within 3 days of delivery yielded slightly better results than within 7 and 10 days.

CONCLUSIONS

The new regression formulas yielded overall similar results, with a small advantage for estimates calculated within 3 days of delivery. Further prospective studies are needed to compare the accuracy of these formulas with those used to date.

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

OBJECTIVES

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

METHODS

In a prospective cohort study, biometric data of 150 singleton fetuses weighing <or= 1600 g at birth were obtained by sonographic examination within 1 week before delivery. Exclusion criteria were multiple pregnancy, intrauterine death as well as major structural or chromosomal anomalies. A new formula was derived using our data, and was then compared with currently available equations for estimating weight in the preterm fetus.

RESULTS

Different statistical estimation strategies were pursued. Gradient boosting with component- wise smoothing splines achieved the best results. The resulting new formula (estimated fetal weight = 656.41 + 1.8321 x volABDO + 31.1981 x HC + 5.7787 x volFEM + 73.5214 x FL + 8.3009 x AC - 449.8863 x BPD + 32.5340 x BPD(2), where volABDO is abdominal volume determined by 3D volumetry, HC is head circumference, volFEM is thigh volume determined by 3D volumetry, FL is femur length and BPD is biparietal diameter) proved to be superior to established equations in terms of mean squared prediction errors, signed percentage errors and absolute percentage errors.

CONCLUSIONS

Our new formula is relatively easy to use and needs no adjustment to weight percentiles or to fetal lie. In fetuses weighing <or= 1600 g at birth it is superior to weight estimation by traditional formulae using two-dimensional measurements.

Could birthweight prediction models be improved by adding fetal subcutaneous tissue thickness?

AIM

The aims of the study were to: (i) compare the accuracy of standard ultrasonic algorithms in the estimation of fetal weight and; (ii) test two new algorithms in order to improve the global performance of birthweight prediction by adding fetal subcutaneous tissue thickness.

METHODS

We enrolled 398 patients who were between 34 and 42 weeks' gestation. Routine ultrasonographic biometric parameters as well as subcutaneous tissue thickness ultrasound parameters were measured. Correlation matrices between ultrasound parameters, in order to evaluate the degree of multicollinearity between these parameters, were assessed to develop a stepwise multiple regression birthweight predictive model.

RESULTS

Contributions of single ultrasound measurements in predicting birthweight were examined, by fitting Log-transformed birthweight versus single ultrasound measurements. We found that the mid-thigh tissue area was able to significantly improve the performance of the birthweight prediction process when added to the other standard ultrasound measurements. We derived two new algorithms which appeared to be better at predicting birthweight. Furthermore there was a lower minimum absolute estimation error noted when compared to other reported formulae.

CONCLUSIONS

Our algorithms showed that the addition of the mid-thigh tissue evaluation in birthweight prediction was valuable in comparison to birthweight prediction models which are based on routine ultrasound parameters.

Estimation of birth weight by two-dimensional ultrasonography: a critical appraisal of its accuracy

OBJECTIVE

To assess the accuracy and characterize two-dimensional ultrasonographic formulas for the estimation of birth weight according to the type of fetal biometric parameters these formulas rely on to make fetal weight predictions.

METHODS

A prospective recruitment of 589 pregnant women was carried out for this cross-sectional study. Different biometric parameters were taken ultrasonographically to estimate birth weight using 35 different formulas. Only those patients who delivered within 48 hours were considered for the analysis (n=441). Differences between the estimated and actual birth weight were assessed by percentage error, accuracy in predictions within +/-10% and +/-15% of error, and use of the Bland-Altman method. All formulas were assessed individually and clustered on the basis of the type of fetal biometric information that they incorporate.

RESULTS

Twenty-nine formulas provided an overall mean absolute percentage error less than or equal to 10%, with overall predictions within +/-10% and +/-15% of the actual birth weight (69.2% and 86.5%, respectively). Twenty formulas showed a good accuracy (bias 0.50 or less) and low variability (mean standard deviation 1.2). Among the categorized algorithms, formulas based on head-abdomen-femur measurements showed the lowest mean absolute percentage error. Upon stratification for birth weight, the group of formulas that rely on abdomen and femur measurements performed best for fetuses weighing more than 3,500 g (P<.01).

CONCLUSION

Our findings show that most formulas are relatively accurate at predicting birth weight up to 3,500 g, and all algorithms tend to underestimate large fetuses.

LEVEL OF EVIDENCE

III.

Ultra-som tridimensional na avaliação do volume de membros fetais

O volume de membros fetais é conhecido marcador do estado nutricional e de crescimento intra-uterino. O surgimento da ultra-sonografia tridimensional tem permitido avaliação volumétrica mais precisa, principalmente de estruturas com formas irregulares, como é o caso dos órgãos fetais. A ultra-sonografia tridimensional pelo modo multiplanar surge como o método mais eficiente para a avaliação do volume de membros fetais, tornando-se o exame mais acurado para a predição de peso ao nascimento. Atualmente, por meio desse método, já se consegue monitorar o desenvolvimento do tecido macio, sendo capaz de diagnosticar mais precocemente os distúrbios do crescimento intra-uterino. Em nosso meio, em que há altos índices de desvios do crescimento fetal e ao mesmo tempo baixa assistência neonatal de qualidade, a maior difusão do método poderia contribuir de forma decisiva para a diminuição nos índices de morbidade e mortalidade perinatais.

Accuracy of ultrasound biometry in the prediction of macrosomia: a systematic quantitative review

OBJECTIVE

To determine the accuracy of ultrasonographically estimated fetal weight (EFW) and abdominal circumference (AC) in the prediction of macrosomia.

DESIGN

Systematic quantitative review.

METHODS

Studies were identified without language restrictions from MEDLINE (1966-2003), EMBASE (1980-2003), Cochrane Library (2003:4), SCISEARCH (1974-2003) and manual searching of bibliographies of known primary and review articles. Studies were selected if accuracy of ultrasonographically EFW or AC was evaluated for predicting macrosomia using birthweight as the reference standard. Data were extracted on study characteristics, quality and accuracy. Data were pooled to produce summary receiver operating characteristic curves (sROC) for studies with various test thresholds. Summary likelihood ratios for positive (LR+) and negative (LR-) test results were generated for an EFW of 4000 g and an AC of 36 cm for predicting birthweight of over 4000 g.

MAIN OUTCOME MEASURES

Birthweight over various thresholds.

RESULTS

There were 36 primary articles consisting of 63 accuracy studies (51 evaluating the accuracy of EFW, and 12 accuracy of fetal AC), including a total of 19,117 women. The sROC area for EFW was not different from the area for fetal AC (0.87 vs 0.85, P= 0.91). For predicting a birthweight of over 4000 g, the summary LRs were 5.7 (95% CI: 4.3 to 7.6) for a positive test and 0.48 (95% CI: 0.38 to 0.60) for a negative test, using Hadlock's method of ultrasonographically estimating fetal weight. For ultrasound fetal AC of 36 cm, the respective LRs for predicting a birthweight over 4000 g were 6.9 (95% CI: 5.2 to 9.0) and 0.37 (0.30-0.45).

CONCLUSION

There is no difference in accuracy between ultrasonographically EFW and AC in the prediction of a macrosomic baby at birth. A positive test result is more accurate for ruling in macrosomia than a negative test result for ruling it out.

Fetal upper arm volume in predicting intrauterine growth restriction: a three-dimensional ultrasound study

As fetuses with intrauterine growth restriction (IUGR) may have increased risks with perinatal morbidity and mortality, prenatal diagnosis of IUGR is a very important issue in perinatology. To assess the efficacy of fetal upper arm volume in predicting IUGR, we undertook a prospective, cross-sectional study using quantitative three-dimensional (3D) ultrasound (US). In total, 40 fetuses with IUGR and 442 fetuses without IUGR were included for the upper arm volume assessment in utero by 3D US. All the fetuses were singletons and were followed up to delivery to establish whether they were complicated with IUGR or not. Our results showed that fetal upper arm volume assessed by 3D US can differentiate fetuses with IUGR from fetuses without IUGR well. The best predicting threshold for IUGR is at the 10th percentile by upper arm volume. Using the 10th percentile as the cutoff, the sensitivity of fetal upper arm volume in predicting IUGR was 97.5%, with specificity 92.8%, predictive value of positive test 54.9%, predictive value of negative test 99.8% and accuracy 93.1%. Furthermore, upper arm volume is the best parameter for detecting IUGR among the common fetal biometric indices, such as biparietal diameter (BPD), occipitofrontal diameter (OFD), head circumference (HC), abdominal circumference (AC), femur length (FL) and estimated fetal weight (EFW). In conclusion, fetal upper arm volume assessed by quantitative 3D US can be used to predict fetuses with IUGR antenatally. We believe fetal upper arm volume assessment by 3D US would be a useful test in detecting fetuses with IUGR.

Ultrasound diagnosis of fetal macrosomia: a comparison of weight prediction models using computer simulation

OBJECTIVE

To assess the frequency of the diagnosis of macrosomia in relation to differing weight estimation formulae in unselected pregnancies.

METHODS

Computer modeling techniques were employed. Computer modeling software generated correlated fetal biometry measurements according to published British standards, from 37 to 41 weeks' gestation. For each set of measurements, estimated fetal weights were obtained by a panel of 18 ultrasound weight formulae. The diagnosis of macrosomia was made if the fetal weight estimate was greater than 4500 g. Cohorts of 5000 pregnancies for each week of gestation were studied.

RESULTS

The frequency of diagnosis of macrosomia increased progressively with advancing gestational age, with large increases between 40 and 41 weeks. The type of weight estimation formula had a profound influence on the frequency of diagnosis of macrosomia. Five of the formulae tested almost never returned a weight estimate greater than 4500 g. Three formulae yielded false positive rates in excess of 15%. The Hadlock group of formulae yielded frequencies of 0.3% to 14.6%.

CONCLUSIONS

Most formulae tend to over-diagnose macrosomia at term. Intervention rates for suspected fetal macrosomia may be influenced by gestational age at the time of scan and the type of fetal weight estimation formula in use.