Estimation of birth weight by use of ultrasonographic formulas targeted to large-, appropriate-, and small-for-gestational-age fetuses

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.

Prospective verification of sonographic fetal weight estimators among term parturients in Uganda

BACKGROUND

Accuracy of fetal weight estimation by ultrasound is essential in making decisions on the time and mode of delivery. There are many proposed formulas for fetal weight estimation such as Hadlock 1, Hadlock 2, Hadlock 3, Hadlock 4 and Shepard. What best applies to the Ugandan population is not known since no verification of any of the formulas has been done before. The primary aim of this study was to determine the accuracy of sonographic estimation of fetal weight using five most commonly used formulas, and analyze formula variations for different weight ranges.

METHODS

This was a hospital based prospective cohort study at Mulago National Referral Hospital, Kampala, Uganda. A total of 356 pregnant women who consented and were within 3 days of birth were enrolled. Prenatal ultrasound fetal weight determined by measuring the biparietal diameter, head circumference, abdominal circumference, femoral length, and then was compared with actual birth weight.

RESULTS

The overall accuracy of Hadlock 1, Hadlock 2, Hadlock 3, Hadlock 4 and Shepard formula were 66.9, 73.3, 77.3, 78.4 and 69.7% respectively. All Hadlocks showed significant mean difference between weight estimates and actual birth weight (p < 0.01) whereas Shepard formula did not [p - 0.2], when no stratification of fetal weights was done. However, all Hadlocks showed a none significant (p-values > 0.05) mean difference between weight estimates and actual birth weight when the actual birth weight was ≥4000.0 g. Shepard weight estimates showed a none significant mean difference when actual birth weight was < 4000 g. Bland-Altman graphs also showed a better agreement of weight estimated by Shepard formula and actual birth weights.

CONCLUSION

All the five formulas were accurate at estimating actual birth weights within 10% accuracy. However, this accuracy varied with the fetal birth weight. Shepard was more accurate in estimating actual birth weights < 4000 g whereas all Hadlocks were more accurate when the actual birthweight was ≥4000 g.

Fetal Weight Estimation Using Automated Fractional Limb Volume With 2-Dimensional Size Parameters in Diabetic Pregnancies

OBJECTIVES

To examine the effect of adding automated fetal fractional limb volume (FLV) with conventional 2-dimensional (2D) fetal weight estimation procedures in a cohort of diabetic pregnancies.

METHODS

A pilot study of diabetic pregnancies measured standard fetal biometry within 7 days of delivery. Fractional arm volume (AVol) and fractional thigh volume (TVol) soft tissue parameters were measured with a commercially available automated software utility (5D Limb Vol; Samsung Medison Co, Ltd, Seoul, Korea). Three conventional weight prediction models that included only 2D size parameters were compared to FLV models that included AVol or TVol. Estimated and actual birth weight (BW) were assessed for the mean percent difference ± standard deviation of the percent differences. Systematic errors were evaluated by the Student t test, and random errors were compared by the Pitman test for correlated variances. The proportion of neonates with estimated fetal weight within 10% of BW was compared between groups by the McNemar test.

RESULTS

Ninety gravid women were enrolled with pregestational (26.7%) or gestational (73.3%) diabetes. All prediction models were accurate, with the exception of small underestimations by the model of Schild et al (-3.8%; Ultrasound Obstet Gynecol 2004; 23:30-35). Random errors for the AVol (6.2%) and TVol (6.9%) models were significantly more precise than the other 3 prediction models: Hadlock et al (7.8%; Am J Obstet Gynecol 1985; 151:333-337), INTERGROWTH-21st (8.0%; Ultrasound Obstet Gynecol 2017; 49:478-486), and Schild et al (8.6%; P < .01). The greatest proportion of cases with BW ±10% was also classified by the AVol (91.1%) and TVol (91.1%) models, followed by Hadlock (83.3%), INTERGROWTH-21st (78.9%), and Schild (76.7%) predictions.

CONCLUSIONS

The addition of automated FLV measurements to conventional 2D biometry was associated with improved weight predictions in this cohort of diabetic pregnancies.

The management of error in ultrasound fetal growth monitoring

It is important to understand the uncertainty in fetal measurements when using them in the management of pregnancy. The aim of this essay is to provide background on errors and uncertainty, describing error sources and their potential impact, with guidance on improving accuracy. Errors can be systematic or random, arising from equipment, image plane selection, measurement method and caliper placement and influenced by image quality, training and experience. The uncertainty in measurements is larger than clinically significant differences in fetal size and growth. Errors can be reduced by implementing equipment acceptance testing, written procedures, training and audit.

Ultrasound Fetal Weight Estimation in Diabetic Pregnancies

OBJECTIVES

To evaluate different formulas for estimating fetal weight in diabetic pregnancies.

METHODS

This retrospective study evaluated the precision of ultrasound fetal weight estimation in 756 pregnancies complicated by gestational diabetes between 2002 and 2016. The estimated fetal weights (EFWs) were obtained within 7 days of delivery from 10 weight estimation formulas and were compared with pair-wise matched controls from 15,701 patients. The precision of the evaluated formulas for EFW was analyzed by median absolute percentage errors (MAPEs), mean percentage errors (MPEs), and proportions of estimates within 10% of actual birth weight.

RESULTS

Among the tested formulas, the lowest MAPE was detected with formula I of Hadlock et al (Am J Obstet Gynecol 1985; 151:333-337), and the formula of Schild et al (Ultrasound Obstet Gynecol 2004; 23:30-35) had the highest proportion of estimates within the 10% range. The EFW in diabetic patients showed a slight trend toward overestimation in comparison with the matched controls (MPE estimates showed a trend toward more positive values). In most of the EFW formulas that were evaluated, no significant differences were detected in MAPEs and estimates within the 10% range. The MPE estimates with most formulas in both groups were close to zero. Overall, the differences between most of the evaluated formulas were small.

CONCLUSIONS

Little evidence was found for differences in the accuracy of the EFW in diabetic pregnancies and controls. The Hadlock I formula showed the lowest MAPE, and the Schild formula had the highest proportion of estimates within the 10% range.

Prediction of fetal macrosomia using two-dimensional and three-dimensional ultrasound

OBJECTIVE

The estimation of the fetal weight by three-dimensional (3D) ultrasound (US) with fractional thigh volume (TVol) has been suggested to be more accurate than two-dimensional (2D) US particularly within the context of fetuses at risk of macrosomia. The objective of this study was to compare the accuracy of 2D US and 3D US with two different methods of projection for the identification of fetal macrosomia at term.

STUDY DESIGN

Prospective study which included women at risk for fetal macrosomia referred for fetal biometry between 34⁺⁰-36⁺⁶ weeks. The estimated fetal weight (EFW) was computed using 2D US and the Hadlock Model IV or through 3D US and the Model VI by Lee et al. The projection of the EFW at the time of delivery was performed by using Yudkin's chart percentiles and the gestation-adjusted projection (GAP) method.

RESULTS

Overall, 230 patients were included. Paired comparison between 2D-US-EFW and 3D-US-EFW with either method of projection of the EFW at birth suggested different properties of the techniques, being 2D-US-EFW associated with higher sensitivity and 3D-US-EFW with higher specificity, PPV and LR + . At ROC curve no difference was found in the prediction of birthweight ≥90th centile using 2D-US-EFW or 3D-US-EFW (AUC 0.831, 95%CI 0.768-0.894 versus AUC 0.860, 95%CI 0.799-0.920, respectively, p 0.37) nor in the prediction of birthweight >95th centile with 2D-US-EFW compared to 3D-US-EFW (0.803, 95%CI 0.731-0.874 versus 0.866, 95%CI 0.805-0.926, respectively, p 0.07). Similarly, a non-significant difference in the accuracy of the prediction of birthweight >4000 g (AUC 0.788, 95%CI 0.716-0.859 for 2D-US-EFW vs AUC 0.802, 95%CI 0.723-0.880 for 3D-US-EFW, p 0.72) and >4500 g (0.828, 95%CI 0.720-0.936 for 2D-US-EFW vs 0.858, 95%CI 0.759-0.956 for 3D-US-EFW, p 0.71) with the GAP method could be demonstrated.

CONCLUSIONS

Within a population at risk of fetal macrosomia the performance of 3D-US-EFW is similar to that of 2D-US-EFW in the prediction of macrosomia at term regardless of the method used for the projection of the EFW, however different properties were noted between the two techniques. Such finding suggests a potential complementary role of the techniques which warrants evaluation in future research.

Prenatal prediction of postnatal large-for-dates neonates using a simplified MRI method: comparison with conventional 2D ultrasound estimates

OBJECTIVE

To evaluate the performance of a simple semi-automated method for estimation of fetal weight (EFW) using magnetic resonance imaging (MRI) as compared with two-dimensional (2D) ultrasound (US) for the prediction of large-for-dates neonates.

METHODS

Data of two groups of women with singleton pregnancy between March 2011 and May 2016 were retrieved from our database and evaluated retrospectively: the first group included women who underwent US-EFW and MRI-EFW within 48 h before delivery and the second group included women who had these evaluations between 35 + 0 weeks and 37 + 6 weeks of gestation, more than 48 h before delivery. US-EFW was based on Hadlock et al. and MRI-EFW on the formula described by Baker et al. For MRI-EFW, planimetric measurement of the fetal body volume (FBV) was performed using a semi-automated method and the time required for measurement was noted. Outcome measure was the performance of MRI-EFW vs US-EFW in the prediction of large-for-dates neonates, both ≤ 48 h and > 48 h before delivery. Receiver-operating characteristics (ROC) curves for each method were compared using the DeLong method.

RESULTS

Of the 270 women included in the first group, 48 (17.8%) newborns had birth weight ≥ 90^th centile and 30 (11.1%) ≥ 95^th centile. The second group included 83 women, and nine (10.8%) newborns had birth weight ≥ 95^th centile. Median time needed for FBV planimetric measurements in all 353 fetuses was 3.5 (range, 1.5-5.5) min. The area under the ROC curve (AUC) for prediction of large-for-dates neonates by prenatal MRI performed within 48 h before delivery was significantly higher than that by US (for birth weight ≥ 90^th centile, difference between AUCs = 0.085, standard error (SE) = 0.020, P < 0.001; for birth weight ≥ 95^th centile, difference between AUCs = 0.036, SE = 0.014, P = 0.01). Similarly, MRI-EFW was better than US-EFW in predicting birth weight ≥ 95^th centile when both examinations were performed > 48 h prior to delivery (difference between AUCs = 0.077, SE = 0.039, P = 0.045).

CONCLUSION

MRI planimetry using our purpose-designed semi-automated method is not time-consuming. The predictive performance of MRI-EFW performed immediately prior to or remote from delivery is significantly better than that of US-EFW for the prediction of large-for-dates neonates. Copyright © 2017 ISUOG. Published by John Wiley & Sons Ltd.

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.

The systematic error in the estimation of fetal weight and the underestimation of fetal growth restriction

Fetal growth restriction (FGR) is associated with an increased risk of perinatal morbidity and mortality and has lifetime implications for the risk of chronic medical conditions. Antenatal diagnosis of FGR remains poor, with the majority of cases remaining undiagnosed. Although several factors contribute to the underdiagnosis of FGR, the error in ultrasound estimation of fetal weight (EFW) generally is not considered in clinical practice. In this commentary, we suggest that the intrinsic, or systematic, error in ultrasound EFW is a significant factor contributing to the underestimation of fetuses predicted to have FGR and should be incorporated into screening and surveillance recommendations. To illustrate this point, we present an analytic model of published data from the Eunice Kennedy Shriver National Institute of Child Health and Human Development Fetal Growth Studies characterizing and quantifying the impact of the systematic error in ultrasound EFW on the underdiagnosis of FGR. Independent of the centile at which the risk of adverse outcome related to FGR begins, whether the 10th, 5th or 3rd percentile, our analysis suggests the need to modify to the current paradigm for identifying and responding to fetuses estimated to be at risk.

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.

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.

Predicting birth weight with conditionally linear transformation models

Low and high birth weight (BW) are important risk factors for neonatal morbidity and mortality. Gynecologists must therefore accurately predict BW before delivery. Most prediction formulas for BW are based on prenatal ultrasound measurements carried out within one week prior to birth. Although successfully used in clinical practice, these formulas focus on point predictions of BW but do not systematically quantify uncertainty of the predictions, i.e. they result in estimates of the conditional mean of BW but do not deliver prediction intervals. To overcome this problem, we introduce conditionally linear transformation models (CLTMs) to predict BW. Instead of focusing only on the conditional mean, CLTMs model the whole conditional distribution function of BW given prenatal ultrasound parameters. Consequently, the CLTM approach delivers both point predictions of BW and fetus-specific prediction intervals. Prediction intervals constitute an easy-to-interpret measure of prediction accuracy and allow identification of fetuses subject to high prediction uncertainty. Using a data set of 8712 deliveries at the Perinatal Centre at the University Clinic Erlangen (Germany), we analyzed variants of CLTMs and compared them to standard linear regression estimation techniques used in the past and to quantile regression approaches. The best-performing CLTM variant was competitive with quantile regression and linear regression approaches in terms of conditional coverage and average length of the prediction intervals. We propose that CLTMs be used because they are able to account for possible heteroscedasticity, kurtosis, and skewness of the distribution of BWs.

A New Sonographic Weight Estimation Formula for Small-for-Gestational-Age Fetuses

OBJECTIVES

The purpose of this study was to develop a new specific weight estimation formula for small-for-gestational-age (SGA) fetuses that differentiated between symmetric and asymmetric growth patterns.

METHODS

A statistical estimation technique known as component-wise gradient boosting was applied to a group of 898 SGA fetuses (symmetric, n = 750; asymmetric, n = 148). A new formula was derived from the data obtained and was then compared to other commonly used equations.

RESULTS

The new formula derived is as follows: estimated fetal weight = e^[1.3734627 + 0.0057133 × biparietal diameter + 0.0011282 × head circumference + 0.0201147 × abdominal circumference + 0.0183081 × femur length - 0.0000177 × biparietal diameter(2) - 0.0000018 × head circumference(2) - 0.0000297 × abdominal circumference(2) -0.0001007 × femur length(2) + 0.0397563 × I(sex = male) + 0.0064505 × gestational age (days) + 0.0096528 × I(SGA = asymmetric)], where the function I denotes an indicator function, which is 1 if the expression is fulfilled (sex = male; SGA type = asymmetric) and otherwise 0. In the whole study group and the 2 subgroups, the new formula showed the lowest median absolute percentage error, mean percentage error, and random error and the best distribution of absolute percentage errors within prespecified error bounds.

CONCLUSIONS

The new formula substantially improves weight estimation in SGA fetuses.

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.

Evaluation of the accuracy of ultrasonography fetal weight estimation models; assessing regression formulae in a Turkish population

In this study, we aimed to evaluate the accuracy of fetal weight prediction, to investigate the validity of sonographic fetal anthropometric parameters in a Turkish population and to assess the most commonly used sonographic formulas for estimation of fetal birth weight. Our retrospective, cross-sectional study included 126 singleton deliveries between June 2010 and January 2011, at the Department of Obstetrics and Gynecology of the GATA Haydarpaşa Training Hospital. Ultrasonography measurement results were applied to nine different fetal weight estimation formulas. Mean error, mean absolute error, mean percentage error and mean absolute percentage error rates were calculated. Under- or overestimation rates and correlation coefficients were also calculated. Fetal biparietal diameter (BPD) and abdominal circumference (AC) were significantly correlated with the actual birth weight and the power analysis for both parameters was calculated as 81%. The highest correlation coefficients in our general population were those of the F1 (Hadlock 1) and F2 (Hadlock 2) models. The highest mean percentage error was detected on F8 (Merz 2) model. Fetal weight estimation modalities were observed to give the best results in a weight range of 3,000 and 3,500 g. Regression formulae used in our population, in general, tended to underestimate, however Hadlock 1 and 2 formulations provided the most accurate results. The Hadlock 1 formula estimated the closest to the actual birth weight in fetuses expected to be born under 3,000 g or over 3,500 g.

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.

Birth weight and neonatal adiposity prediction using fractional limb volume obtained with 3D ultrasound

INTRODUCTION

The objective of this investigation was to study fetal thigh volume throughout gestation and explore its correlation with birth weight and neonatal body composition. This novel technique may improve birth weight prediction and lead to improved detection rates for fetal growth restriction.

MATERIALS AND METHODS

Fractional thigh volume (TVol) using 3D ultrasound, fetal biometry and soft tissue thickness were studied longitudinally in 42 mother-infant pairs. The percentages of neonatal body fat, fat mass and fat-free mass were determined using air displacement plethysmography. Correlation and linear regression analyses were performed.

RESULTS

Linear regression analysis showed an association between TVol and birth weight. TVol at 33 weeks was also associated with neonatal fat-free mass. There was no correlation between TVol and neonatal fat mass. Abdominal circumference, estimated fetal weight (EFW) and EFW centile showed consistent correlations with birth weight. Thigh volume demonstrated an additional independent contribution to birth weight prediction when added to the EFW centile from the 38-week scan (p = 0.03).

CONCLUSION

Fractional TVol performed at 33 weeks gestation is correlated with birth weight and neonatal lean body mass. This screening test may highlight those at risk of fetal growth restriction or macrosomia.

Sonographic fetal weight estimation - is there more to it than just fetal measurements?

OBJECTIVES

The primary aim of this study was to evaluate the effects of different maternal, fetal, and examiner related factors on the accuracy of sonographic fetal weight estimation (SFWE).

METHODS

A retrospective cohort study analyzing 9064 SFWEs performed within 1 week prior to delivery, including singleton pregnancies with a gestational age of 37 to 42 weeks, was recorded at one medical center from January 2004 to September 2011. Predicted birth weights were calculated according to models by Sabbagha et al., Hadlock et al., and Combs et al. and were compared with the actual birth weight. Effects of different factors on SFWE accuracy were assessed. The systematic error, random error, and mean absolute percentage error were used as measures of accuracy.

RESULTS

High maternal weight, height, body mass index, multiparity, older maternal age, diabetes, and fetal male sex were associated with underestimation of SFWE (P < 0.05). Fetal presentation and the sonographer's experience influenced SFWE differently using various models. The amniotic fluid index did have a significant effect on SFWE. Overall, more than 90% of the systematic errors were unaccounted for in the factors we assessed.

CONCLUSIONS

Many maternal and fetal factors significantly influence the SFWE; nevertheless, most errors are probably due to inherent problems in SFWE formulas.

Using Akaike information criterion and minimum mean square error mode in compensating for ultrasonographic errors for estimation of fetal weight by new operators

OBJECTIVES

The accuracy of ultrasound (US) measurements is operator dependent. In order to decrease the operator-dependent errors in estimated fetal weight (EFW), a model selection analysis was undertaken to select significant compensation weighting factors on ultrasonographic parameters to support artificial neural network (ANN), and thus to enhance the accuracy of fetal weight estimation.

MATERIALS AND METHODS

In total, 2127 singletons were examined by prenatal US within 3 days before delivery for ANN development, and another 100 cases were selected from new operators for evaluation. First, correlation analysis was used to analyze the differences between the prenatal and postnatal parameters. Second, Akaike information criterion (AIC) was used to determine the number of database partition and optimal weightings for compensating the input parameters of the ANN model. Finally, minimum mean squared error (MMSE) mode was utilized to determine the optimal EFW.

RESULTS

EFW of the proposed compensation model using AIC and MMSE showed mean absolute percent error of 5.1 ± 3.1% and mean absolute error of 158.9 ± 96.2 g. When comparing the accuracy of EFW, our model using AIC and MMSE was superior to those conventional EFW formulas (all p < 0.05).

CONCLUSION

We proved that performing the parameter compensation (by AIC) and model compensations (by MMSE) for the ANN model can improve EFW accuracy. Our AIC-MMSE model of EFW will contribute to the improvement of accuracy when adding new US datasets measured by new operators.

Fetal weight estimation: comparison of two-dimensional US and MR imaging assessments

PURPOSE

To prospectively define fetal density in the second half of pregnancy by using magnetic resonance (MR) imaging and to compare estimates of fetal weight based on ultrasonography (US) and MR imaging with actual birth weight.

MATERIALS AND METHODS

Written informed consent was obtained for this ethics committee-approved study. In this cross-sectional study between March 2011 and May 2012, fetal density was calculated as actual birth weight at delivery divided by fetal body volume at MR imaging in 188 fetuses between 20 weeks and 2 days and 42 weeks and 1 day of gestational age. Regression analysis was used to investigate the effect of variables, including sex, on fetal density. The US estimate of fetal weight was performed according to Hadlock et al, and the MR estimate of fetal weight was calculated based on the equation developed by Baker et al. US and MR estimates of fetal weight were compared with actual birth weights by using regression analysis.

RESULTS

Median fetal density was equal to 1.04 (range, 0.95-1.18). Fetal density was significantly associated with gestational age at delivery but not with fetal sex. In 26.6% of fetuses, the US estimate of fetal weight had a relative error of more than 10%, while a similar relative error for the MR estimate of fetal weight occurred in only 1.1% of fetuses. The limits of agreement were narrower with the MR estimate of fetal weight compared with the US estimate of fetal weight.

CONCLUSION

In the second half of pregnancy, fetal density varies with gestational age. Fetal weight estimates by using fetal MR imaging are better than those by using prenatal US.

Efficient fetal size classification combined with artificial neural network for estimation of fetal weight

OBJECTIVES

A novel analysis was undertaken to select a significant ultrasonographic parameter (USP) for classifying fetuses to support artificial neural network (ANN), and thus to enhance the accuracy of fetal weight estimation.

METHODS

In total, 2127 singletons were examined by prenatal ultrasound within 3 days before delivery. First, correlation analysis was used to determine a significant USP for fetal grouping. Second, K-means algorithm was utilized for fetal size classification based on the selected USP. Finally, stepwise regression analysis was used to examine input parameters of the ANN model.

RESULTS

The estimated fetal weight (EFW) of the new model showed mean absolute percent error (MAPE) of 5.26 ± 4.14% and mean absolute error (MAE) of 157.91 ± 119.90 g. Comparison of EFW accuracy showed that the new model significantly outperformed the commonly-used EFW formulas (all p < 0.05).

CONCLUSION

We proved the importance of choosing a specific grouping parameter for ANN to improve EFW accuracy.

Ultrasonographic weight estimation in large for gestational age fetuses: a comparison of 17 sonographic formulas and four models algorithms

OBJECTIVE

To evaluate the accuracy of different formulas and role of fetal parameters (cephalic, abdominal, femur) used for estimation fetal weight (EFW) in large for gestational age (LGA) fetus in diabetic and non-diabetic mothers.

METHODS

Seventeen formulas were assessed individually and clustered in four algorithms (X, Y, Z, W) on the basis of fetal biometric parameters using the mean absolute % error, standard deviation (SD), prediction within +/-5%, +/-10%, +/-15% of error and introducing new variable hypotenuse test (HPT) that can sum up precision and accuracy of formulas employed. For predicting fetal macrosomia (BW > or = 4200 g) a receiver-operating characteristic curve was constructed.

RESULTS

Warsof2 formula showed the lowest mean % error, SD and HPT (p < 0.01) with overall prediction +/-5, +/-10%, +/-15% of birth weight in 68, 94 and 98%. The formulas that were only based on abdominal measurement (Warsof2, Hadlock1, Campbell) showed the best ability to identify fetal macrosomia. The X algorithm confirming primary role of abdominal circumference for EFW in diabetic mothers.

CONCLUSIONS

Accuracy of EFW in LGA fetuses is attributable to the biometric parameters used. Our findings show that the best formulas for EFW are those which only consider the abdominal measurements, especially in diabetic mothers. The new variable that we propose (HPT) confirms this result.

Defining normal and abnormal fetal growth: promises and challenges

Normal fetal growth is a critical component of a healthy pregnancy and influences the long-term health of the offspring. However, defining normal and abnormal fetal growth has been a long-standing challenge in clinical practice and research. We review various references and standards that are used widely to evaluate fetal growth and discuss common pitfalls of current definitions of abnormal fetal growth. Pros and cons of different approaches to customize fetal growth standards are described. We further discuss recent advances toward an integrated definition for fetal growth restriction. Such a definition may incorporate fetal size with the status of placental health that is measured by maternal and fetal Doppler velocimetry and biomarkers, biophysical findings, and genetics. Although the concept of an integrated definition appears promising, further development and testing are required. An improved definition of abnormal fetal growth should benefit both research and clinical practice.

Improving obstetric estimation of outcomes of extremely premature neonates: an evolving challenge

AIMS

A clinically useful website at the US National Institutes of Child Health and Human Development (NICHD) uses an algorithm based on a recent publication to estimate peri-viable neonatal outcomes. This algorithm uses gestational age, ultrasound estimated fetal weight (EFW), fetal sex, and the use of antenatal corticosteroids as the basis for estimation of outcomes and when used after birth is superior to such estimation by gestational age alone. Because one might be tempted to use this algorithm with obstetric patients, we tested its clinical applicability.

METHODS

We reviewed the literature using search terms relating to the above clinical factors. Next, we gathered data from the website. The range of outcomes for neonates was then estimated using the uncertainty derived for these clinical factors before birth from the literature review and the NICHD website algorithm.

RESULTS

We found increased uncertainty for estimating outcomes, as a function of the greater uncertainty in knowledge of the clinical factors in obstetrics as opposed to neonatology.

CONCLUSIONS

The imprecision during the time before birth seriously restricts the obstetric use of the NICHD algorithm at this time. Refining the precision of the algorithm prior to birth is necessary.

Incorporation of femur length leads to underestimation of fetal weight in asymmetric preterm growth restriction

OBJECTIVE

To review the performance of a variety of biometry formulae for estimated fetal weight (EFW) in the management of severely growth restricted fetuses with abnormal umbilical artery Doppler at a single perinatal institution.

METHODS

Forty-three pregnancies were retrospectively reviewed. Inclusion criteria were: chromosomally/ structurally normal fetus; complete ultrasound biometry at < or = 7 days from delivery; EFW < 10(th) centile; absent/reversed end-diastolic flow in the umbilical arteries; and delivery at < 32 + 6 weeks. EFW accuracy and precision were compared among nine formulae utilizing combinations of head circumference (HC), biparietal diameter (BPD), abdominal circumference (AC) and femur length (FL) measurements.

RESULTS

Twenty-six (60.5%) fetuses showed asymmetric growth (HC/AC ratio > 95(th) centile). Analysis of the systematic and random errors associated with each formula showed that the birth weight of asymmetrically-grown fetuses was most closely approximated by the Hadlock equation that utilized BPD and AC measurements only. The birth weight of symmetrically-grown fetuses was most closely approximated by EFW derived from Hadlock equations that utilized > or = three biometry measurements, including FL. Incorporation of FL into Hadlock formulae led to significant underestimation of birth weight in the fetuses with asymmetric growth (mean percentage error +/- SD: EFW(FL-AC), -13.3 +/- 9.8%; EFW(BPD-FL-AC), -10.8 +/- 9.8%; EFW(HC-FL-AC), -11.8 +/- 9.3%; EFW(BPD-HC-FL-AC), -11.7 +/- 9.5%; P < 0.001). The same equations were accurate in fetuses with symmetric growth (EFW(FL-AC), 3.1 +/- 10.0%; EFW(BPD-FL-AC), 1.0 +/- 8.9%; EFW(HC-FL-AC), 0.3 +/- 8.7%; EFW(BPD-HC-FL-AC), 0.4 +/- 15.5%). Use of the best performing equation (Hadlock 3), which does not include FL, to estimate weight in asymmetrically-grown fetuses over 28 weeks' gestation, would have reduced the proportion of those with an underestimation of fetal weight of > 100 g from nine (50.0%) to three (16.7%).

CONCLUSIONS

Biometry methods that exclude FL should be considered in asymmetric intrauterine growth restriction associated with abnormal umbilical artery Doppler waveforms.

Morphological and functional evaluation of normal and abnormal fetal growth by ultrasonography

Correction or estimation of gestational age is essential for the evaluation of fetal growth. When necessary, an appropriate fetal biometric parameter should be selected depending on fetal size. In the first trimester, crown-rump length (CRL) is appropriate, especially when the CRL is 20-40 mm. In the second trimester, biparietal diameter (BPD), head circumference (HC), and femur length (FL) are of equal predictability. Fetal weight estimation is still the basis of evaluation of fetal growth. The most predictable formula currently available includes the parameters BPD (or HC), abdominal circumference (AC), and FL. Serial measurements of AC are useful for diagnosis of intrauterine growth restriction (IUGR) and macrosomia. Quantitative evaluation of soft tissue deposition may be informative for macrosomia. Functional evaluation using Doppler velocimetry is essential in IUGR cases associated with uteroplacental insufficiency. Analysis of blood velocity waveforms of the umbilical and intracranial arteries, predominantly the middle cerebral artery, is widely performed. An increase in the pulsatility index (PI) or resistance index (RI) of the umbilical artery and/or a decrease in the PI or RI of the middle cerebral artery are highly predictable for fetal hypoxia and/or acidosis.

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.

Shoulder dystocia

Shoulder dystocia is an unpredictable obstetrical emergency that results in serious complications especially to the neonate. Such complications include fracture of the clavicle, brachial plexus injury, fracture of the humerus and asphyxia.1-4 The incidence of shoulder dystocia appears to be increasing5 and its unpredictability continues to be the nightmare of the obstetrician. The following is a review of risk factors which are associated with shoulder dystocia, a critical review of the usefulness of antenatal ultrasound in the prediction of the macrosomic fetus and a discussion of the controversies surrounding the management of shoulder dystocia.

An informative probability model enhancing real time echobiometry to improve fetal weight estimation accuracy

A multinormal probability model is proposed to correct human errors in fetal echobiometry and improve the estimation of fetal weight (EFW). Model parameters were designed to depend on major pregnancy data and were estimated through feed-forward artificial neural networks (ANNs). Data from 4075 women in labour were used for training and testing ANNs. The model was implemented numerically to provide EFW together with probabilities of congruence among measured echobiometric parameters. It enabled ultrasound measurement errors to be real-time checked and corrected interactively. The software was useful for training medical staff and standardizing measurement procedures. It provided multiple statistical data on fetal morphometry and aid for clinical decisions. A clinical protocol for testing the system ability to detect measurement errors was conducted with 61 women in the last week of pregnancy. It led to decisive improvements in EFW accuracy.

Clinical and sonographic estimation of fetal weight performed during labor by residents

OBJECTIVE

This study was undertaken to assess the accuracy of both clinical and sonographic estimations of the fetal weight (EFW) performed during the active phase of labor by residents.

METHODS

The study protocol consisted of achieving clinical, followed by sonographic EFW by the admitting resident during the active phase of labor. Patients who had an EFW (clinical or sonographic) within the last 2 weeks were excluded from the study. In addition, the effect of the following variables on the accuracy of the EFW were examined: maternal age, maternal weight and body mass index, parity, the Bishop score before obtaining the EFW, gestational age, birth weight, and the postgraduate year of the examiner. The Pearson correlation, chi2 test, and Student t test were the statistical analyses used. We also calculated the sensitivity, specificity, and positive and negative predictive values for clinical and sonographic EFW for detecting macrosomia (birth weight > or = 4000 g).

RESULTS

A total of 192 patients participated in this study. The coefficient of correlation between the clinical and sonographic EFW and the actual birth weight was 0.59 (P < .0001) and 0.65 (P < .0001), respectively. Clinical EFW was correct (within +/-10%) in 72% of the cases and the sonographic EFW was correct (within +/-10%) in 74% of the cases. However, the sensitivity of predicting birth weight of 4 kg or more was only 50% for both clinical and sonographic EFW, with 95% and 97% specificity, respectively. None of the clinical variables that were tested were significantly associated with the accuracy of the EFW.

CONCLUSION

Both clinical and sonographic EFW performed during the active phase of labor by residents correlate with the actual birth weight but have poor sensitivity in detecting macrosomic fetuses. Sonographic EFWs offer no advantage over clinical EFWs.

A systematic review of the ultrasound estimation of fetal weight

OBJECTIVES

The range and use of ultrasound fetal measurements have gradually been extended. Measurements have been combined to estimate fetal weight by mathematically based non-linear regression analysis or physically based volumetric methods. Fetal weight estimation is inaccurate, with poor sensitivity for prediction of fetal compromise. Several authors have shown the unacceptable level of intra- and interobserver variability in fetal measurement and the impact of errors on growth assessment. The aims of this study were to review the available methods and possible sources of inaccuracy.

METHODS

Four databases were searched for studies comparing ultrasound estimated fetal weight (EFW) with birth weight. Studies meeting the inclusion criteria evaluated 11 different methods. Errors were graphically summarized.

RESULTS

No consistently superior method has emerged. Volumetric methods provide some theoretical advantages. Random errors are large and must be reduced if clinical errors are to be avoided.

CONCLUSIONS

The accuracy of EFW is compromised by large intra- and interobserver variability. Efforts must be made to minimize this variability if EFW is to be clinically useful. This may be achieved through averaging of multiple measurements, improvements in image quality, uniform calibration of equipment, careful design and refinement of measurement methods, acknowledgment that there is a long learning curve, and regular audit of measurement quality. Further work to improve the universal validity and accuracy of fetal weight estimation formulae is also required.

Ultrasound estimation of fetal weight with the use of computerized artificial neural network model

The aim of this study was to test if the computerized artificial neural network (ANN) model could improve ultrasound (US) estimation of fetal weight over estimation with the other commonly used formulas generated from regression analysis. First, as the training group, we performed US examinations on 991 singleton fetuses within 3 days of delivery. Six input variables were used to construct the ANN model: biparietal diameter (BPD), occipitofrontal diameter (OFD), abdominal circumference (AC), femur length (FL), gestational age and fetal presentation. Second, a total of 362 fetuses were assessed subsequently as the validation group. In this training group, the ANN model was better than the other compared formulas in fetal weight estimation (n = 991, mean absolute error 183.83 g, mean absolute percent error 6.02%, all p < 0.0001). In addition, the validation group further proved the results (n = 362, mean absolute error 179.91 g, mean absolute percent error 6.15%, all p < 0.005). In conclusion, the computerized artificial neural network (ANN) model could provide better US estimation of fetal weight than estimations by means of commonly used formulas generated from regression analysis.

Fetal biometry: clinical, pathological, and technical considerations

Sonographic measurements of fetal ultrasound parameters are the basis for accurate determination of gestational age and detection of fetal growth abnormalities. Selection of the most useful single biometric parameter depends on the timing and purpose of measurement and is influenced by specific limitations. CRL (crown-rump length) is the best parameter for early dating of pregnancy. Biparietal diameter (BPD) maintains the closest correlation with gestational age in the second trimester. In cases of variation in the shape of the skull, head circumference is an effective alternative. Abdominal circumference is the most useful dimension to evaluate fetal growth, and femur length is the best parameter in the evaluation of skeletal dysplasia. Use of multiple predictors improves the accuracy of estimates. An individual approach to each pregnancy is recommended for fetal growth assessment. The various epidemiological factors involved in fetal growth should be considered and specific charts for different communities should be used when possible. The methods of fetal weight estimation with their limitations and potential errors are presented. Clinical application of fetal biometry in abnormal growth is discussed in cases of small- and large-for-gestational-age fetuses, chromosomal aberrations, and skeletal dysplasias.

Estimation of fetal weight before and after amniotomy in the laboring gravid woman

OBJECTIVE

This study was undertaken to search for differences between fetal weights estimated both ultrasonographically and clinically before and after amniotomy in laboring gravid women.

STUDY DESIGN

Estimates of fetal weight (ultrasonographic and clinical) were obtained for laboring gravid women before and after amniotomy. These estimates were compared with actual birth weights determined post partum.

RESULTS

One hundred sixty-two patients completed the study protocol. Comparisons made with unpaired Student t test analyses demonstrated a difference (P <.001) between ultrasonographically estimated fetal weights before and after amniotomy. Simple regression analysis showed a correlation between both ultrasonographic and clinical estimates of fetal weight and actual birth weights before and after amniotomy, with postamniotomy clinical estimates having the strongest correlation (ultrasonographic preamniotomy estimate, R = 0.717; ultrasonographic postamniotomy estimate, R = 0.630; clinical preamniotomy estimate, R = 0.742; and clinical postamniotomy estimate, R = 0.788). Of all ultrasonographic parameters measured, preamniotomy abdominal circumference correlated best with actual birth weight (R = 0.730).

CONCLUSION

Clinical estimates of fetal weight after amniotomy correlated well with actual birth weights. Preamniotomy abdominal circumference was the ultrasonographic parameter best for prediction of actual birth weight. Maternal weight affected clinical but not ultrasonographic estimates of fetal weight in this study. However, clinical estimates of fetal weight were actually superior to ultrasonographic estimates of fetal weight in this study.

Positive predictive value of suspected growth aberration in twin gestations

OBJECTIVE

Our purpose was to determine the positive predictive value of ultrasonographic surveillance for growth abnormalities in twin gestations as a function of gestational age.

STUDY DESIGN

Women with twin gestations and delivery between January 1992 and March 1998 who had a 20- to 24-week sonogram with normal fetal anatomic findings and who had at least 1 sonogram showing abnormal growth were identified. Abnormal growth on ultrasonography was defined as an estimated fetal weight <10th percentile, abdominal circumference <5th percentile, or twin discordance (>20% difference in twin weights as a function of the heavier twin). Birth weights were then assessed for evidence of twin discordance or growth restriction.

RESULTS

The positive predictive value for the occurrence of a growth abnormality at birth, after an abnormal growth finding on ultrasonography at any time during gestation, was 47.7%. The positive predictive value was greatest (85%) when suspected growth restriction was first documented at 20 to 24 weeks of gestation and decreased with increasing gestational age. Even though sonograms were obtained at a mean interval of 4.4 +/- 2.0 weeks, those gestations with normal growth at 20 to 24 weeks had an elapsed time of 10.3 +/- 3.9 weeks until a growth abnormality was subsequently detected.

CONCLUSION

In twin gestations the positive predictive value of a sonogram for a growth abnormality at birth is significantly decreased after normal findings on a 20- to 24-week sonogram. This finding suggests that a routine 2- to 4-week interval between sonograms for all twin gestations may be unwarranted.

Fetal weight estimation and prediction of fetal macrosomia in non-diabetic pregnant women

In the present study we investigated the accuracy of Shepard's formula in the sonographic diagnosis of macrosomic fetus of non-diabetic pregnant women. Three hundred and eighty-one macrosomic and 450 appropriate for gestational age (AGA) fetuses born to non-diabetic mothers between 37-42 weeks of gestation were included in the study. Ultrasonographic fetal weight estimation within two days of delivery was made using Shepard's formula in all patients. The estimated fetal weights were compared with the actual birth weights of the same subjects. We did not observe any macrosomic newborn birth in pregnant women with 3200 g or less fetal weight estimation. However, in patients with 3400-3499 g fetal weight estimation, a statistically significant increase in macrosomic newborn birth was observed. Only 3.2% of newborns having actual birth weights greater than or equal to 4000 g had sonographic birth weight estimation less than 4000 g. Accuracy of weight estimations using the Shepard's formula was found to be low in macrosomic fetus. On the other hand, increased incidence of macrosomic newborn birth was observed in subjects with ultrasonographic fetal weight estimations above 3400 g and this level may be useful as a cut-off value for prediction of macrosomic fetus in non-diabetic pregnant women.

A comparison between ultrasound and clinical methods for predicting fetal weight

Fetal weight prediction by different methods were compared. Those methods were ultrasound fetal weight estimations using Campbell, Warsof and Hadlock equations, and clinical subjective estimation by experienced obstetricians, as well as clinical objective studies (Zayed's equation). We evaluated 523 Jordanian (Arabic) patients in labour. Our results shows that ultrasound equation provides the highest accuracy in predicting fetal weight. In this study Hadlock's equation was more precise than the other equations. There is still a place for clinical fetal weight estimation, especially if objection methods are used.