An evaluation of two equations for predicting fetal weight by ultrasound

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.

Prediction of Neonatal Growth Restriction in Fetuses With Gastroschisis by Early Third Trimester Ultrasonography Utilizing Contemporary Birth Weight Percentiles

OBJECTIVE

To identify the estimated fetal weight (EFW) formula and threshold for the optimal prediction of fetal growth restriction (FGR) at 26-34 weeks' in fetuses with gastroschisis.

METHODS

Late second and third trimester ultrasound data were used to calculate the EFW utilizing eight different formulas: Hadlock I-IV, Honarvar, Shepard, Siemer, and Warsof. EFW and birth weight percentiles were assigned from US population growth curves. FGR and small for gestational age (SGA) were defined as EFW and birth weight less than the tenth percentile for gestational age; Receiver operating characteristic (ROC) curves were used to compare formula performance for FGR diagnosis at 26-34 weeks' to identify an SGA birth weight.

RESULTS

There were 170 newborns with gastroschisis; 46 (27%) were SGA. The mean gestational age at the time of ultrasound was 30.8 ± 1.7 weeks. The mean gestational age at birth was 36.3 ± 1.7 weeks. ROC curve analysis found the Hadlock III formula had the largest area under the curve (AUC) of 0.813 closely followed by Hadlock IV (AUC = 0.811) and Hadlock II (AUC = 0.808) for diagnosis of FGR correlating to neonatal SGA diagnosis. Hadlock II, Hadlock III, and Hadlock IV had the highest diagnostic accuracies when compared to the other EFW formulas.

CONCLUSIONS

The Hadlock II, Hadlock III, and Hadlock IV formulas have comparable predictive performance in the optimal identification of FGR in fetuses with gastroschisis at 26-34 weeks'. A threshold of an EFW less than the 25.2th percentile is suggested.

Diagnosis of Pregnancy Complications Using Blind Ultrasound Sweeps Performed by Individuals Without Prior Formal Ultrasound Training

OBJECTIVE

To estimate the diagnostic accuracy of blind ultrasound sweeps performed with a low-cost, portable ultrasound system by individuals with no prior formal ultrasound training to diagnose common pregnancy complications.

METHODS

This is a single-center, prospective cohort study conducted from October 2020 to January 2022 among people with second- and third-trimester pregnancies. Nonspecialists with no prior formal ultrasound training underwent a brief training on a simple eight-step approach to performing a limited obstetric ultrasound examination that uses blind sweeps of a portable ultrasound probe based on external body landmarks. The sweeps were interpreted by five blinded maternal-fetal medicine subspecialists. Sensitivity, specificity, and positive and negative predictive values for blinded ultrasound sweep identification of pregnancy complications (fetal malpresentation, multiple gestations, placenta previa, and abnormal amniotic fluid volume) were compared with a reference standard ultrasonogram as the primary analysis. Kappa for agreement was also assessed.

RESULTS

Trainees performed 194 blinded ultrasound examinations on 168 unique pregnant people (248 fetuses) at a mean of 28±5.85 weeks of gestation for a total of 1,552 blinded sweep cine clips. There were 49 ultrasonograms with normal results (control group) and 145 ultrasonograms with abnormal results with known pregnancy complications. In this cohort, the sensitivity for detecting a prespecified pregnancy complication was 91.7% (95% CI 87.2-96.2%) overall, with the highest detection rate for multiple gestations (100%, 95% CI 100-100%) and noncephalic presentation (91.8%, 95% CI 86.4-97.3%). There was high negative predictive value for placenta previa (96.1%, 95% CI 93.5-98.8%) and abnormal amniotic fluid volume (89.5%, 95% CI 85.3-93.6%). There was also substantial to perfect mean agreement for these same outcomes (range 87-99.6% agreement, Cohen κ range 0.59-0.91, P<.001 for all).

CONCLUSION

Blind ultrasound sweeps of the gravid abdomen guided by an eight-step protocol using only external anatomic landmarks and performed by previously untrained operators with a low-cost, portable, battery-powered device had excellent sensitivity and specificity for high-risk pregnancy complications such as malpresentation, placenta previa, multiple gestations, and abnormal amniotic fluid volume, similar to results of a diagnostic ultrasound examination using a trained ultrasonographer and standard-of-care ultrasound machine. This approach has the potential to improve access to obstetric ultrasonography globally.

Accuracy and precision of sonographic fetal weight estimation in Sweden

INTRODUCTION

Fetal growth assessment by ultrasound is an essential part of modern obstetric care. The formula by Persson and Weldner for estimated fetal weight (EFW), used in Sweden since decades, has not yet been evaluated. The objective of this study was to evaluate accuracy and precision of the formula by Persson and Weldner, and to compare it to two other formulae using biparietal diameter instead of head circumference.

MATERIAL AND METHODS

The study population consisted of 31 521 singleton pregnancies delivered at 22⁺⁰ gestational weeks or later, with an ultrasound EFW performed within 2 days before delivery, registered in the Swedish Pregnancy Register between 2014 and 2021. Fetal biometric ultrasound measurements were used to calculate EFW according to the formulae by Persson and Weldner, Hadlock 2 and Shepard. Bland-Altman analysis, systematic error (mean percentage error), random error (standard deviation [SD] of mean percentage error), proportion of weight estimates within ±10% of birthweight, and proportion with underestimated and overestimated weight was calculated. Moreover, calculations were made after stratification into small, appropriate, and large for gestational age (SGA, AGA and LGA), respectively, and gestational age at examination.

RESULTS

For the formula by Persson and Weldner, MPE was -2.7 (SD 8.9) and the proportion of EFW within ±10% from actual birthweight was 76.0%. MPE was largest for fetuses estimated as severe SGA (<3rd percentile, -5.4) and for the most preterm fetuses (<24 weeks, -5.4). For Hadlock 2 and Shepard's formulae, MPE were 3.9 (SD 8.9) and 3.4 (SD 9.7), respectively, and the proportions of EFW within ±10% from actual birthweight were 69.4% and 67.1%, respectively. MPE was largest for fetuses estimated as severe LGA (>97th percentile), 7.6 and 9.4, respectively.

CONCLUSIONS

The recommended Swedish formula by Persson and Weldner is generally accurate for fetal weight estimation. The systematic underestimation of EFW and random error is largest in extreme preterm and estimated SGA-fetuses, which is of importance in clinical decision making. The accuracy of EFW with the formula by Persson and Weldner is as good as or better than Hadlock 2 and Shepard's formulae.

Accuracy of estimated fetal weight in extremely preterm infants and the impact of prepregnancy body mass index

BACKGROUND

Antenatally, we rely on ultrasound estimated fetal weight as a proxy for birthweight to inform discussions regarding perinatal morbidity and mortality. Maternal obesity may negatively impact the quality of ultrasound imaging, and thus, understanding the associations between obesity and estimated fetal weight in the preterm period is important.

OBJECTIVE

Given the rising obesity rates and association with preterm birth, we sought to determine the accuracy of ultrasound-derived estimated fetal weight in predicting birthweight in preterm infants by prepregnancy body mass index and to evaluate the accuracy of estimated fetal weight in predicting birthweight between small-for-gestational-age and appropriate-for-gestational-age infants.

STUDY DESIGN

We included all women who delivered a live-born singleton infant between 23 0/7 and 31 6/7 weeks of gestation and had an ultrasound estimated fetal weight within 7 days before delivery. We calculated the mean percentage difference between estimated fetal weight and birthweight and the absolute percent difference. Excess error was defined as an absolute percentage difference of >20%. We used multivariable modified Poisson models to determine the association between prepregnancy body mass index and small for gestational age and excess ultrasound error.

RESULTS

Our cohort included 641 infants with a mean gestational age of 28.0±2.6 weeks and a mean birthweight of 1110±425 g. More than one-third of our cohort were obese (227 [35%]). The mean percentage difference between estimated fetal weight and birthweight was 7.7%±11.2% among all infants. Ultrasound overestimated birthweight in 77% of the cohort (n=492). Stratified by body mass index, the mean percentage differences between estimated fetal weight and birthweight were 6.7%±11.0% in women with normal weight and 9.5%±12.0% in women with obesity (P=.02). The mean percentage differences between estimated fetal weight and birthweight were 11.0%±11.0% in small-for-gestational-age infants (n=80) and 7.1%±11.0% in appropriate-for-gestational-age infants (P<.001). Small-for-gestational-age infant was associated with an increased risk of excess ultrasound error with an adjusted relative risk of 2.3 (95% confidence interval, 1.2-4.3).

CONCLUSION

Although ultrasound estimated fetal weight overestimated birthweight, particularly in small-for-gestational-age infants, most estimates were within 10% of actual birthweight. Obesity and small-for-gestational-age birth were both associated with an increased risk of excess ultrasound error (≥20%) in estimating birthweight.

Fetal magnetic resonance imaging at 36 weeks predicts neonatal macrosomia: the PREMACRO study

BACKGROUND

Large-for-gestational-age fetuses are at increased risk of perinatal morbidity and mortality. Magnetic resonance imaging seems to be more accurate than ultrasound in the prediction of macrosomia; however, there is no well-powered study comparing magnetic resonance imaging with ultrasound in routine pregnancies.

OBJECTIVE

This study aimed to prospectively compare estimates of fetal weight based on 2-dimensional ultrasound and magnetic resonance imaging with actual birthweights in routine pregnancies.

STUDY DESIGN

From May 2016 to February 2019, women received counseling at the 36-week clinic. Written informed consent was obtained for this Ethics Committee-approved study. In this prospective, single-center, blinded study, pregnant women with singleton pregnancies between 36 0/7 and 36 6/7 weeks' gestation underwent both standard evaluation of estimated fetal weight with ultrasound according to Hadlock et al and magnetic resonance imaging according to the formula developed by Baker et al, based on the measurement of the fetal body volume. Participants and clinicians were aware of the results of the ultrasound but blinded to the magnetic resonance imaging estimates. Birthweight percentile was considered as the gold standard for the ultrasound and magnetic resonance imaging-derived percentiles. The primary outcome was the area under the receiver operating characteristic curve for the prediction of large-for-gestation-age neonates with birthweights of ≥95th percentile. Secondary outcomes included the comparative prediction of large-for-gestation-age neonates with birthweights of ≥90th, 97th, and 99th percentiles and small-for-gestational-age neonates with birthweights of ≤10th, 5th, and 3rd percentiles for gestational age and maternal and perinatal complications.

RESULTS

Of 2914 women who were initially approached, results from 2378 were available for analysis. Total fetal body volume measurements were possible for all fetuses, and the time required to perform the planimetric measurements by magnetic resonance imaging was 3.0 minutes (range, 1.3-5.6). The area under the receiver operating characteristic curve for the prediction of a birthweight of ≥95th percentile was 0.985 using prenatal magnetic resonance imaging and 0.900 using ultrasound (difference=0.085, P<.001; standard error, 0.020). For a fixed false-positive rate of 5%, magnetic resonance imaging for the estimation of fetal weight detected 80.0% (71.1-87.2) of birthweight of ≥95th percentile, whereas ultrasound for the estimation of fetal weight detected 59.1% (49.0-68.5) of birthweight of ≥95th percentile. The positive predictive value was 42.6% (37.8-47.7) for the estimation of fetal weight using magnetic resonance imaging and 35.4% (30.1-41.1) for the estimation of fetal weight using ultrasound, and the negative predictive value was 99.0% (98.6-99.3) for the estimation of fetal weight using magnetic resonance imaging and 98.0% (97.6-98.4) for the estimation of fetal weight using ultrasound. For a fixed false-positive rate of 10%, magnetic resonance imaging for the estimation of fetal weight detected 92.4% (85.5-96.7) of birthweight of ≥95th percentile, whereas ultrasound for the estimation of fetal weight detected 76.2% (66.9-84.0) of birthweight of ≥95th percentile. The positive predictive value was 29.9% (27.2-32.8) for the estimation of fetal weight using magnetic resonance imaging and 26.2% (23.2-29.4) for the estimation of fetal weight using ultrasound, and the negative predictive value was 99.6 (99.2-99.8) for the estimation of fetal weight using magnetic resonance imaging and 98.8 (98.4-99.2) for the estimation of fetal weight using ultrasound. The area under the receiver operating characteristic curves for the prediction of large-for-gestational-age neonates with birthweights of ≥90th, 97th, and 99th percentiles and small-for-gestational-age neonates with birthweights of ≤10th, 5th, and 3rd percentiles was significantly larger in prenatal magnetic resonance imaging than in ultrasound (P<.05 for all).

CONCLUSION

At 36 weeks' gestation, magnetic resonance imaging for the estimation of fetal weight performed significantly better than ultrasound for the estimation of fetal weight in the prediction of large-for-gestational-age neonates with birthweights of ≥95th percentile for gestational age and all other recognized cutoffs for large-for-gestational-age and small-for-gestational-age neonates (P<.05 for all).

Accuracy of ultrasound estimation of fetal weight at term: A comparison of shepard and hadlock methods

Background

Ultrasound measurement provides a noninvasive means of obtaining information about fetal weight and may help in necessary preparations at and after delivery. Although some ultrasound methods include only one or two fetal indices, others, to improve accuracy, incorporate either three or all the four fetal indices. The aim of this report is to assess the accuracy of two different methods for fetal weight estimation.

Materials and Methods

This was a prospective study of 170 consecutive pregnant women at term. Ultrasound was used to estimate fetal weight by the Shepard and Hadlock methods, and the actual birth weight (ABW) was determined at birth. The ultrasound-estimated fetal weights (EFWs) and ABW were analyzed.

Results

The women were aged 21-42 years (mean 31.3 ± 7 years). The EFW using the Shepard method was 1.9 kg-5.0 kg (mean 3.6 ± 0.5 kg) and 1.8 kg-4.4 kg (mean 3.3 ± 0.4 kg) for Hadlock method, and ABW was 2.0 kg-4.5 kg (mean 3.4 ± 0.5 kg). The mean EFW using the Shepard method was significantly higher than that of ABW (P < 0.001). The Shepard method significantly overestimated macrosomia compared to that by the ABW. There was no significant difference in microsomia rate between the two methods and ABW.

Conclusion

The Hadlock method was more accurate at estimating fetal weight compared to the Shepard method and is recommended for the ultrasound estimation of fetal weight in our setting and similar settings.

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.

Accuracy of Ultrasound to Predict Neonatal Birth Weight Among Fetuses With Gastroschisis: Impact on Timing of Delivery

OBJECTIVES

To determine the accuracy of ultrasound estimation of fetal weight among fetuses with gastroschisis and how the diagnosis of fetal growth restriction (FGR) affects the timing of delivery.

METHODS

This was a retrospective cohort study including all fetuses with a diagnosis of gastroschisis at our institution from November 2012 through October 2017. We excluded multiple gestations, pregnancies with major structural or chromosomal abnormalities, and those for which prenatal and postnatal follow-up were unavailable. Performance characteristics of ultrasound to predict being small for gestational age (SGA) were calculated for the first and last ultrasound estimations of fetal weight.

RESULTS

Our cohort included 75 cases of gastroschisis. At the initial ultrasound estimation, 15 of 58 (25.9%) fetuses met criteria for FGR; 48 of 70 (68.6%) met criteria at the time of the last ultrasound estimation (median, 34.7 weeks). Cesarean delivery was performed for 37 of 75 (49.3%), with FGR and concern for fetal distress as the indication for delivery in 17 of 37 (45.9%). Only 6 of 17 (35.3%) of the neonates born by cesarean delivery for an indication of FGR and fetal distress were SGA. The initial ultrasound designation of FGR corresponded to SGA at birth in 8 of 15 (53.3%), whereas the last ultrasound estimation corresponded to SGA in 17 of 48 (35.4%). The initial ultrasound estimation agreed with the last ultrasound estimation before delivery with the diagnosis of FGR in 13 of 15 (86.7%).

CONCLUSIONS

Ultrasound in the third trimester was sensitive but had a low positive predictive value and low accuracy for the diagnosis of SGA at birth for fetuses with gastroschisis. A large proportion of fetuses were born by cesarean delivery with indications related to FGR or fetal concerns.

Prediction of fetal weight based on back propagation neural network optimized by genetic algorithm

Fetal weight is an important index to judge fetal development and ensure the safety of pregnant women. However, fetal weight cannot be directly measured. This study proposed a prediction model of fetal weight based on genetic algorithm to optimize back propagation (GA-BP) neural network. Using random number table method, 80 cases of pregnant women in our hospital from September 2018 to March 2019 were divided into control group and observation group, 40 cases in each group. The doctors in the control group predicted the fetal weight subjectively according to routine ultrasound and physical examination. In the observation group, the continuous weight change model of pregnant women was established by using the regression model and the historical physical examination data obtained by feature normalization pretreatment, and then the genetic algorithm (GA) was used to optimize the initial weights and thresholds of back propagation (BP) neural network to establish the fetal weight prediction model. The coincidence rate of fetal weight was compared between the two groups after birth. Results: The prediction error of GA-BPNN was controlled within 6%. And the accuracy of GA-BPNN was 76.3%, which were 14.5% higher than that of traditional methods. According to the error curve, GA-BP is more effective in predicting the actual fetal weight. Conclusion: The GA-BPNN model can accurately and quickly predict fetal weight.

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.

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.

Universal late pregnancy ultrasound screening to predict adverse outcomes in nulliparous women: a systematic review and cost-effectiveness analysis

BACKGROUND

Currently, pregnant women are screened using ultrasound to perform gestational aging, typically at around 12 weeks' gestation, and around the middle of pregnancy. Ultrasound scans thereafter are performed for clinical indications only.

OBJECTIVES

We sought to assess the case for offering universal late pregnancy ultrasound to all nulliparous women in the UK. The main questions addressed were the diagnostic effectiveness of universal late pregnancy ultrasound to predict adverse outcomes and the cost-effectiveness of either implementing universal ultrasound or conducting further research in this area.

DESIGN

We performed diagnostic test accuracy reviews of five ultrasonic measurements in late pregnancy. We conducted cost-effectiveness and value-of-information analyses of screening for fetal presentation, screening for small for gestational age fetuses and screening for large for gestational age fetuses. Finally, we conducted a survey and a focus group to determine the willingness of women to participate in a future randomised controlled trial.

DATA SOURCES

We searched MEDLINE, EMBASE and the Cochrane Library from inception to June 2019.

REVIEW METHODS

The protocol for the review was designed a priori and registered. Eligible studies were identified using keywords, with no restrictions for language or location. The risk of bias in studies was assessed using the Quality Assessment of Diagnostic Accuracy Studies 2 (QUADAS-2) tool. Health economic modelling employed a decision tree analysed via Monte Carlo simulation. Health outcomes were from the fetal perspective and presented as quality-adjusted life-years. Costs were from the perspective of the public sector, defined as NHS England, and the costs of special educational needs. All costs and quality-adjusted life-years were discounted by 3.5% per annum and the reference case time horizon was 20 years.

RESULTS

Umbilical artery Doppler flow velocimetry, cerebroplacental ratio, severe oligohydramnios and borderline oligohydramnios were all either non-predictive or weakly predictive of the risk of neonatal morbidity (summary positive likelihood ratios between 1 and 2) and were all weakly predictive of the risk of delivering a small for gestational age infant (summary positive likelihood ratios between 2 and 4). Suspicion of fetal macrosomia is strongly predictive of the risk of delivering a large infant, but it is only weakly, albeit statistically significantly, predictive of the risk of shoulder dystocia. Very few studies blinded the result of the ultrasound scan and most studies were rated as being at a high risk of bias as a result of treatment paradox, ascertainment bias or iatrogenic harm. Health economic analysis indicated that universal ultrasound for fetal presentation only may be both clinically and economically justified on the basis of existing evidence. Universal ultrasound including fetal biometry was of borderline cost-effectiveness and was sensitive to assumptions. Value-of-information analysis indicated that the parameter that had the largest impact on decision uncertainty was the net difference in cost between an induced delivery and expectant management.

LIMITATIONS

The primary literature on the diagnostic effectiveness of ultrasound in late pregnancy is weak. Value-of-information analysis may have underestimated the uncertainty in the literature as it was focused on the internal validity of parameters, which is quantified, whereas the greatest uncertainty may be in the external validity to the research question, which is unquantified.

CONCLUSIONS

Universal screening for presentation at term may be justified on the basis of current knowledge. The current literature does not support universal ultrasonic screening for fetal growth disorders.

FUTURE WORK

We describe proof-of-principle randomised controlled trials that could better inform the case for screening using ultrasound in late pregnancy.

STUDY REGISTRATION

This study is registered as PROSPERO CRD42017064093.

FUNDING

This project was funded by the National Institute for Health Research (NIHR) Health Technology Assessment programme and will be published in full in Health Technology Assessment; Vol. 25, No. 15. See the NIHR Journals Library website for further project information.

Fetal birthweight prediction with measured data by a temporal machine learning method

Background

Birthweight is an important indicator during the fetal development process to protect the maternal and infant safety. However, birthweight is difficult to be directly measured, and is usually roughly estimated by the empirical formulas according to the experience of the doctors in clinical practice.

Methods

This study attempts to combine multiple electronic medical records with the B-ultrasonic examination of pregnant women to construct a hybrid birth weight predicting classifier based on long short-term memory (LSTM) networks. The clinical data were collected from 5,759 Chinese pregnant women who have given birth, with more than 57,000 obstetric electronic medical records. We evaluated the prediction by the mean relative error (MRE) and the accuracy rate of different machine learning classifiers at different predicting periods for first delivery and multiple deliveries. Additionally, we evaluated the classification accuracies of different classifiers respectively for the Small-for-Gestational-age (SGA), Large-for-Gestational-Age (LGA) and Appropriate-for-Gestational-Age (AGA) groups.

Results

The results show that the accuracy rate of the prediction model using Convolutional Neuron Networks (CNN), Random Forest (RF), Linear-Regression, Support Vector Regression (SVR), Back Propagation Neural Network(BPNN), and the proposed hybrid-LSTM at the 40th pregnancy week for first delivery were 0.498, 0.662, 0.670, 0.680, 0.705 and 0.793, respectively. Among the groups of less than 39th pregnancy week, the 39th pregnancy week and more than 40th week, the hybrid-LSTM model obtained the best accuracy and almost the least MRE compared with those of machine learning models. Not surprisingly, all the machine learning models performed better than the empirical formula. In the SGA, LGA and AGA group experiments, the average accuracy by the empirical formula, logistic regression (LR), BPNN, CNN, RF and Hybrid-LSTM were 0.780, 0.855, 0.890, 0.906, 0.916 and 0.933, respectively.

Conclusions

The results of this study are helpful for the birthweight prediction and development of guidelines for clinical delivery treatments. It is also useful for the implementation of a decision support system using the temporal machine learning prediction model, as it can assist the clinicians to make correct decisions during the obstetric examinations and remind pregnant women to manage their weight.

Reduced growth velocity from the mid-trimester is associated with placental insufficiency in fetuses born at a normal birthweight

BACKGROUND

Fetal growth restriction (FGR) due to placental insufficiency is a major risk factor for stillbirth. While small-for-gestational-age (SGA; weight < 10th centile) is a commonly used proxy for FGR, detection of FGR among appropriate-for-gestational-age (AGA; weight ≥ 10th centile) fetuses remains an unmet need in clinical care. We aimed to determine whether reduced antenatal growth velocity from the time of routine mid-trimester ultrasound is associated with antenatal, intrapartum and postnatal indicators of placental insufficiency among term AGA infants.

METHODS

Three hundred and five women had biometry measurements recorded from their routine mid-trimester (20-week) ultrasound, at 28 and 36 weeks' gestation, and delivered an AGA infant. Mid-trimester, 28- and 36-week estimated fetal weight (EFW) and abdominal circumference (AC) centiles were calculated. The EFW and AC growth velocities between 20 and 28 weeks, and 20-36 weeks, were examined as predictors of four clinical indicators of placental insufficiency: (i) low 36-week cerebroplacental ratio (CPR; CPR < 5th centile reflects cerebral redistribution-a fetal adaptation to hypoxia), (ii) neonatal acidosis (umbilical artery pH < 7.15) after the hypoxic challenge of labour, (iii) low neonatal body fat percentage (BF%) reflecting reduced nutritional reserve and (iv) placental weight < 10th centile.

RESULTS

Declining 20-36-week fetal growth velocity was associated with all indicators of placental insufficiency. Each one centile reduction in EFW between 20 and 36 weeks increased the odds of cerebral redistribution by 2.5% (odds ratio (OR) = 1.025, P = 0.001), the odds of neonatal acidosis by 2.7% (OR = 1.027, P = 0.002) and the odds of a < 10th centile placenta by 3.0% (OR = 1.030, P < 0.0001). Each one centile reduction in AC between 20 and 36 weeks increased the odds of neonatal acidosis by 3.1% (OR = 1.031, P = 0.0005), the odds of low neonatal BF% by 2.8% (OR = 1.028, P = 0.04) and the odds of placenta < 10th centile by 2.1% (OR = 1.021, P = 0.0004). Falls in EFW or AC of > 30 centiles between 20 and 36 weeks were associated with two-threefold increased relative risks of these indicators of placental insufficiency, while low 20-28-week growth velocities were not.

CONCLUSIONS

Reduced growth velocity between 20 and 36 weeks among AGA fetuses is associated with antenatal, intrapartum and postnatal indicators of placental insufficiency. These fetuses potentially represent an important, under-recognised cohort at increased risk of stillbirth. Encouragingly, this novel fetal assessment would require only one additional ultrasound to current routine care, and adds to the potential benefits of routine 36-week ultrasound.

Fetal ultrasound estimated weight and correlation to Brazilian newborn weight

Background: To compare the best fetal weight formula with different biometric tables on the weight of Brazilian newborns. Methods: This observational study has tested the performance of different common fetal weight formulas and biometric tables. Weight estimates were performed by the methods of Warsof et al. (1977), Shepard et al. (1982), Hadlock et al. (1985), Furlan et al. (2012) and Stirnemann et al. (2017). The biometric tables selected were the following: Snijders and Nicolaides (1994), Hadlock et al. (1984), Papageorghiou et al. (2014) and Kiserud et al. (2016) and correlated to Pedreira et al. (2011) database, which was considered the gold standard. Statistical analyses were performed using the mean relative error, average absolute error and the Pearson correlation coefficient (r). Results: The best r was found when using the Snijders and Nicolaides (1994) biometric table with weight formula by Stirnemann et al. (2017). The average relative error was lower when using weight formula by Shepard et al. (1982) with biometric tables by Snijders and Nicolaides (1994), Papageorghiou et al. (2014) or Kiserud et al. (2016). On average, absolute error, the lowest r was obtained for the Furlan et al. (2012) weight formula and the Papageorghiou et al. (2014) biometric table. Conclusions: The best correlation was found for biometric table by Snijders and Nicolaides (1994) and fetal weight formula calculation for the estimation of Brazilian newborn weight by Stirnemann et al. (2017).

Background: To compare the best fetal weight formula with different biometric tables on the weight of Brazilian newborns. Methods: This observational study has tested the performance of different common fetal weight formulas and biometric tables. Weight estimates were performed by the methods of Warsof et al. (1977), Shepard et al. (1982), Hadlock et al. (1985), Furlan et al. (2012) and Stirnemann et al. (2017). The biometric tables selected were the following: Snijders and Nicolaides (1994), Hadlock et al. (1984), Papageorghiou et al. (2014) and Kiserud et al. (2016) and correlated to Pedreira et al. (2011) database, which was considered the gold standard. Statistical analyses were performed using the mean relative error, average absolute error and the Pearson correlation coefficient (r). Results: The best r was found when using the Snijders and Nicolaides (1994) biometric table with weight formula by Stirnemann et al. (2017). The average relative error was lower when using weight formula by Shepard et al. (1982) with biometric tables by Snijders and Nicolaides (1994), Papageorghiou et al. (2014) or Kiserud et al. (2016). On average, absolute error, the lowest r was obtained for the Furlan et al. (2012) weight formula and the Papageorghiou et al. (2014) biometric table. Conclusions: The best correlation was found for biometric table by Snijders and Nicolaides (1994) and fetal weight formula calculation for the estimation of Brazilian newborn weight by Stirnemann et al. (2017).

Intrauterine growth discordance across gestation and birthweight discordance in dichorionic twins

BACKGROUND

Although intertwin size difference is an important measure of fetal growth, the appropriate cut point to define discordance is unclear. Few studies have assessed intertwin differences in estimated fetal weight longitudinally or in relation to size differences at birth.

OBJECTIVES

The objectives of the study were to estimate the magnitude of percentage differences in estimated fetal weight across gestation in dichorionic twins in relation to a fixed discordance cut point and compare classification of aberrant fetal growth by different measures (estimated fetal weight differences, birthweight discordance, small for gestational age).

STUDY DESIGN

Women aged 18-45 years from 8 US centers with dichorionic twin pregnancies at 8 weeks 0 days to 13 weeks 6 days gestation planning to deliver in participating hospitals were recruited into the Eunice Kennedy Shriver National Institute of Child Health and Human Development Fetal Growth Studies-Dichorionic Twins study and followed through delivery (n = 140; 2012-2013). Ultrasounds were conducted at 6 targeted study visits to obtain fetal biometrics and calculate estimated fetal weight. Percent estimated fetal weight and birthweight differences were calculated: ([weight_larger - weight_smaller]/weight_larger)*100; discordance was defined as ≥18% for illustration. Birth sizes for gestational age (both, 1, or neither small for gestational age) were determined; twins were categorized into combined birthweight plus small for gestational age groups: birthweight discordance ≥18% (yes, no) with both, 1, or neither small for gestational age. Linear mixed-models estimated percentiles of estimated fetal weight percent differences across gestation and compared estimated fetal weight differences between combined birthweight discordance and small for gestational age groups. A Fisher exact test compared birthweight discordance and small for gestational age classifications.

RESULTS

Median estimated fetal weight percentage difference increased across gestation (5.9% at 15.0, 8.4% at 38.0 weeks), with greater disparities at higher percentiles (eg, 90th percentile: 15.6% at 15.0, 26.3% at 38.0 weeks). As gestation advanced, an increasing percentage of pregnancies were classified as discordant using a fixed cut point: 10% at 27.0, 15% at 34.0, and 20% at 38.0 weeks. Birthweight discordance and small for gestational age classifications differed (P = .002); for birthweight discordance ≥18% vs <18%: 44% vs 71% had neither small for gestational age; 56% vs 18% had 1 small for gestational age; no cases (0%) vs 11% had both small for gestational age, respectively. Estimated fetal weight percent difference varied across gestation by birthweight discordance plus small for gestational age classification (P = .040). Estimated fetal weight percentage difference increased with birthweight discordance ≥18% (neither small for gestational age: 0.46%/week [95% confidence interval, 0.08-0.84]; 1 small for gestational age: 0.57%/week [95% confidence interval, 0.25-0.90]) but less so without birthweight discordance (neither small for gestational age: 0.17%/week [95% confidence interval, 0.06-0.28]; 1 small for gestational age: 0.03%/week [95% confidence interval, -0.17 to 0.24]); both small for gestational age: 0.10%/week [95% confidence interval, -0.15 to 0.36]).

CONCLUSION

The percentage of dichorionic pregnancies exceeding a fixed discordance cut point increased over gestation. A fixed cut point for defining twin discordance would identify an increasing percentage of twins as discordant as gestation advances. Small for gestational age and percentage weight differences assess distinct aspects of dichorionic twin growth. A percentile cut point may be more clinically useful for defining discordance, although further study is required to assess whether any specific percentile cut point correlates to adverse outcomes.

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.

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.

Does the Porter formula hold its promise? A weight estimation formula for macrosomic fetuses put to the test

Purpose

Estimating fetal weight using ultrasound measurements is an essential task in obstetrics departments. Most of the commonly used weight estimation formulas underestimate fetal weight when the actual birthweight exceeds 4000 g. Porter et al. published a specially designed formula in an attempt to improve detection rates for such macrosomic infants. In this study, we question the usefulness of the Porter formula in clinical practice and draw attention to some critical issues concerning the derivation of specialized formulas of this type.

Methods

A retrospective cohort study was carried out, including 4654 singleton pregnancies with a birthweight ≥ 3500 g, with ultrasound examinations performed within 14 days before delivery. Fetal weight estimations derived using the Porter and Hadlock formulas were compared.

Results

Of the macrosomic infants, 27.08% were identified by the Hadlock formula, with a false-positive rate of 4.60%. All macrosomic fetuses were detected using the Porter formula, with a false-positive rate of 100%; 99.96% of all weight estimations using the Porter formula fell within a range of 4300 g ± 10%. The Porter formula only provides macrosomic estimates.

Conclusions

The Porter formula does not succeed in distinguishing macrosomic from normal-weight fetuses. High-risk fetuses with a birthweight ≥ 4500 g in particular are not detected more precisely than with the Hadlock formula. For these reasons, we believe that the Porter formula should not be used in clinical practice. Newly derived weight estimation formulas for macrosomic fetuses must not be based solely on a macrosomic data set.

Electronic supplementary material

The online version of this article (10.1007/s00404-019-05410-7) contains supplementary material, which is available to authorized users.

Evaluating the accuracy and precision of sonographic fetal weight estimation models in extremely early-onset fetal growth restriction

INTRODUCTION

Birthweight is a critical predictor of survival in extremely early-onset fetal growth restriction (diagnosed pre-28 weeks' gestation, with abnormal umbilical/uterine artery Doppler waveforms), therefore accurate fetal weight estimation is a crucial component of antenatal management. Currently available sonographic fetal weight estimation models were predominantly developed in populations of mixed gestational age and varying fetal weights, but not specifically tested within the context of extremely early-onset fetal growth restriction. This study aimed to determine the accuracy and precision of fetal weight estimation in this population and investigate whether model performance is affected by other factors.

MATERIAL AND METHODS

Cases where a growth scan was performed within 48 hours of delivery (n = 65) were identified from a cohort of extremely early-onset fetal growth-restricted pregnancies at a single tertiary maternity center (n = 159). Fetal biometry measurements were used to calculate estimated fetal weight using 21 previously published models. Systematic and random errors were calculated for each model and used to identify the best performing model, which in turn was used to explore the relationship between error and gestation, estimated fetal weight, fetal presentation, fetal asymmetry and amniotic fluid volume.

RESULTS

Both systematic (median 8.2%; range -44.1 to 49.5%) and random error (median 11.6%; range 9.7-23.8%) varied widely across models. The best performing model was Hadlock head circumference-abdominal circumference-femur length (HC-AC-FL), regardless of gestational age, fetal size, fetal presentation or asymmetry, with an overall systematic error of 1.5% and random error of 9.7%. Despite this, it only calculated the estimated fetal weight within 10% of birthweight in 64.6% of cases. There was a weak negative relation between mean percentage error with Hadlock HC-AC-FL and amniotic fluid volume, suggesting fetal weight is overestimated at lower liquor volumes and underestimated at higher liquor volumes (P = 0.002, adjusted R²  = 0.08).

CONCLUSIONS

Hadlock HC-AC-FL is the most accurate model currently available to estimate fetal weight in extremely early-onset fetal growth restriction independent of gestation or fetal size, asymmetry or presentation. However, for 35.4% of cases in this study, estimated fetal weight calculated using this model deviates by more than 10% from birthweight, highlighting a need for an improved model.

Estimation of fetal weight using Hadlock's formulas: Is head circumference an essential parameter?

OBJECTIVES

To test the equivalence of two fetal weight estimation formulas generated by Hadlock, a formula that includes head circumference parameter (H1), and another (H2) which excludes this parameter. A secondary aim was to identify the patients in which H2 formula is less reliable to use.

STUDY DESIGN

This retrospective cohort study included a total of 1220 sonographic fetal weight estimations performed within seven days of delivery and recorded at a single medical center from January 2014 to December 2016. Estimated fetal weight was calculated using H1 and H2 formulas. Their accuracies were compared using percentage error, the proportion of weight estimations falling within ±15% error interval and by Bland-Altman analysis. Multivariate regression was performed to evaluate factors affecting weight estimation by H2 formula.

RESULTS

The mean birth weight was 3288.92 ± 641.27gr. The H2 formula presented with statistically significant higher value of systemic mean percent error comparing to H1 (3.19% vs. 1.87%, p < 0.001 respectively). H2 formula had a lower accuracy compared to H1 in predicting fetal weight within ±15% of birth weight (90.49% vs. 93.44%, p < 0.01 respectively). Using Bland-Altman analysis, the 95% limits of agreement between both formulas were (-142.03) to 231.79gr with a mean of 44.88gr. Factors found to influence significantly on H2 formula were long femur length (OR 1.144, p < 0.0001) and low maternal age (OR 0.947, p < 0.01).

CONCLUSIONS

H1formula was more accurate than H2 formula in predicting fetal weight at term. However, the accuracy difference was found to be small. Therefore, if ultrasonographic evaluation of HC is technically difficult, Hadlock formula that excludes head circumference can be used with confidence. Caution should be paid with higher values of femur length and lower maternal age.

The use of magnetic resonance imaging in the prediction of birthweight

Extremes of fetal growth can increase adverse pregnancy outcomes, and this is equally applicable to single and multiple gestations. Traditionally, these cases have been identified using simple two-dimensional ultrasound which is quite limited by its low precision. Magnetic resonance imaging (MRI) has now been used for many years in obstetrics, mainly as an adjunct to ultrasound for congenital abnormalities and increasingly as part of the post-mortem examination. However, MRI can also be used to accurately assess fetal weight as first demonstrated by Baker et al in 1994, using body volumes rather than standard biometric measurements. This publication was followed by several others, all of which confirmed the superiority of MRI; however, despite this initial promise, the technique has never been successfully integrated into clinical practice. In this review, we provide an overview of the literature, detail the various techniques and formulas currently available, discuss the applicability to specific high-risk groups and present our vision for the future of MRI within clinical obstetrics.

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.

Fetal abdominal wall defects in an Australian tertiary setting: contemporary characteristics, ultrasound accuracy, and outcome

PURPOSE

In this study, we aimed to comprehensively evaluate risk factors, ultrasound estimation of fetal weight, prenatal management, and pregnancy outcomes of gastroschisis and omphalocele at a metropolitan Australian hospital.

MATERIAL AND METHODS

This was a retrospective single-center cohort study from 2006 to 2014 at a tertiary hospital with colocated neonatal surgical facilities. Demographic, pregnancy, ultrasound, birth and neonatal data were compared between gastroschisis and omphalocele. Correlation between routine (Hadlock 1 &2) and specific (Siemer) estimated fetal weight (EFW) estimation formulae with birth weight (BW) was made for those 50 gastroschisis cases with ≥2 third trimester scans and last scan ≤2 weeks prior to birth.

RESULTS

There were 126 abdominal wall defects: 83 gastroschisis and 43 omphalocele. Consistent with international literature, the average maternal age was lower for gastroschisis and rates of smoking higher, while there were more intrauterine deaths and pregnancy terminations in omphalocele. Gastroschisis mothers were more likely living outside Sydney, had more infections in pregnancy and were followed with a larger number of antenatal visits, with a shorter period from the last visit to birth. In omphalocele pregnancies, amniocentesis was more likely performed, with more abnormal results than in gastroschisis fetuses. All EFW formulae had a good correlation between Z score for the last US and actual BW (ICC 0.693-0.815), with Hadlock 2 being the best. Siemer formula had the best correlation from first to the last scan. Gastroschisis newborns were born earlier (36.8 versus 38.2 wks p = .001), with smaller birthweight (2.52 versus 3.03 kg, p < .001), a longer request of intensive care (central line, parenteral nutrition, intubation) and second surgery, along with more multisystem complications (average 1.5 versus 0.7, p = .004) and a longer hospital stay (58.8 versus 36.8 d, p < .001).

CONCLUSION

Demographic, antenatal, and pregnancy outcome data for abdominal wall defects correlated well with the international literature. Hadlock 1-2 gave the most consistent EFW estimate, with all formulae showing good correlation.

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.

Magnetic resonance imaging for prenatal estimation of birthweight in pregnancy: review of available data, techniques, and future perspectives

Fetuses at the extremes of growth abnormalities carry a risk of perinatal morbidity and death. Their identification traditionally is done by 2-dimensional ultrasound imaging, the performance of which is not always optimal. Magnetic resonance imaging superbly depicts fetal anatomy and anomalies and has contributed largely to the evaluation of high-risk pregnancies. In 1994, magnetic resonance imaging was introduced for the estimation of fetal weight, which is done by measuring the fetal body volume and converting it through a formula to fetal weight. Approximately 10 studies have shown that magnetic resonance imaging is more accurate than 2-dimensional ultrasound imaging in the estimation of fetal weight. Yet, despite its promise, the magnetic resonance imaging technique currently is not implemented clinically. Over the last 5 years, this technique has evolved quite rapidly. Here, we review the literature data, provide details of the various measurement techniques and formulas, consider the application of the magnetic resonance imaging technique in specific populations such as patients with diabetes mellitus and twin pregnancies, and conclude with what we believe could be the future perspectives and clinical application of this challenging technique. The estimation of fetal weight by ultrasound imaging is based mainly on an algorithm that takes into account the measurement of biparietal diameter, head circumference, abdominal circumference, and femur length. The estimation of fetal weight by magnetic resonance imaging is based on one of the 2 formulas: (1) magnetic resonance imaging-the estimation of fetal weight (in kilograms)=1.031×fetal body volume (in liters)+0.12 or (2) magnetic resonance imaging-the estimation of fetal weight (in grams)=1.2083×fetal body volume (in milliliters)ˆ0.9815. Comparison of these 2 formulas for the detection of large-for-gestational age neonates showed similar performance for preterm (P=.479) and for term fetuses (P=1.000). Literature data show that the estimation of fetal weight with magnetic resonance imaging carries a mean or median relative error of 2.6 up to 3.7% when measurements were performed at <1 week from delivery; whereas for the same fetuses, the relative error at 2-dimensional ultrasound imaging varied between 6.3% and 11.4%. Further, in a series of 270 fetuses who were evaluated within 48 hours from birth and for a fixed false-positive rate of 10%, magnetic resonance imaging detected 98% of large-for-gestational age neonates (≥95th percentile for gestation) compared with 67% with ultrasound imaging estimates. For the same series, magnetic resonance imaging applied to the detection of small-for-gestational age neonates ≤10th percentile for gestation, for a fixed 10% false-positive rate, reached a detection rate of 100%, compared with only 78% for ultrasound imaging. Planimetric measurement has been 1 of the main limitations of magnetic resonance imaging for the estimation of fetal weight. Software programs that allow semiautomatic segmentation of the fetus are available from imaging manufacturers or are self-developed. We have shown that all of them perform equally well for the prediction of large-for-gestational age neonates, with the advantage of the semiautomatic methods being less time-consuming. Although many challenges remain for this technique to be generalized, a 2-step strategy after the selection of a group who are at high risk of the extremes of growth abnormalities is the most likely scenario. Results of ongoing studies are awaited (ClinicalTrials.gov Identifier # NCT02713568).

Comparison of the accuracy of INTERGROWTH-21 formula with other ultrasound formulae in fetal weight estimation

OBJECTIVE

A new ultrasound formula for fetal weight estimation was proposed from the INTERGROWTH-21 project in 2017. There is no comparison of its accuracy with other ultrasound formulae. This study aims to compare the accuracy of INTERGROWTH-21 formula in fetal weight estimation with the traditional Hadlock1 and Shepard formula.

MATERIALS AND METHODS

All pregnant patients who had delivery in United Christian Hospital between January to December 2016 were retrospectively reviewed. Those who had prenatal ultrasound scan performed within 7 days of delivery were recruited. Hadlock1, Shepard and INTERGROWTH-21 formula were used to estimate the fetal weight and their accuracies were compared with the actual birthweight of neonates.

RESULTS

A total of 403 patients were recruited. Hadlock1 was the most accurate with the lowest mean absolute percentage error (MAPE) 7.34 when compared with Shepard (9.00; p < 0.001) and INTERGROWTH-21 (9.07; p < 0.001). INTERGROWTH-21 had the lowest proportion of patients having estimated fetal weight within 10% discrepancy from the actual birthweight (57.6%) compared with Hadlock1 (71.2%; p < 0.001) and Shepard (66.3; p = 0.011). Presence of intrauterine growth restriction (IUGR) or fetal macrosomia (>=4000 g) were both associated with significantly higher MAPE in Hadlock1 and INTERGROWTH-21. IUGR (p = 0.005) and macrosomia (p = 0.004) remained significant in the final equation of logistic regression model that affect the precision of fetal weight estimation in Hadlock1, while only IUGR was significant in INTERGROWTH-21 (p < 0.001).

CONCLUSION

INTERGROWTH-21 formula was not shown to be better than the traditional Hadlock1 or Shepard formulae. Future prospective studies would be required to evaluate the accuracy of INTERGROWTH-21 formula especially at the extremes of birthweight.

Top-cited articles in the Journal: a bibliometric analysis

BACKGROUND

The Journal has had a profound influence in nearly 150 years of publishing. A bibliometric analysis, which uses citation analyses to evaluate the impact of articles, can be used to identify the most impactful papers in the Journal's history.

OBJECTIVE

The objective was to identify and characterize the top-cited articles published in the Journal since 1920.

STUDY DESIGN

We used the Web of Science and Scopus databases to identify the most frequently cited articles of the Journal from 1920 through 2018. The top 100 articles from each database were included in our analysis. Articles were evaluated for several characteristics including year of publication, article type, topic, open access, and country of origin. Using the Scopus data, we performed an unadjusted categorical analysis to characterize the articles and a 2 time point analysis to compare articles before and after 1995, the median year of publication from each database list.

RESULTS

The top 100 articles from each database were included in the analysis. This included 120 total articles: 80 articles listed in both and 20 unique in each database. More than half (52%) were observational studies, 9% were RCTs, and 75% were from US authors. When the post-1995 studies were compared with the articles published before 1995, articles were more frequently cited (median 27 vs 13 citations per year, P < .001), more likely to be randomized (14.0% vs 4.8%, P = .009), and more likely to originate from international authors (33.3% vs 17.5%, P = .045).

CONCLUSION

Slightly more than half of the top-cited papers in the Journal since 1920 were observational studies and three quarters of all papers were from US authors. Compared with top-cited papers before 1995, the Journal's top-cited papers after 1995 were more likely to be randomized and to originate from international authors.

The value of ultrasound in predicting isolated inter-twin discordance and adverse perinatal outcomes

PURPOSE

To investigate the value of ultrasound approaching delivery to predict isolated inter-twin discordance and adverse perinatal outcomes.

METHODS

We retrospectively included twin pregnancies with sonography approaching delivery in ten maternal-foetal medicine centres in China from 2013 to 2014. Estimated foetal weight (EFW) and inter-twin EFW disparity (EFWD) were calculated based on biometry parameters. Percentage errors between EFW and actual birthweight or between EFWD and actual inter-twin disparity were calculated. ROC curves and multiple logistic regression were applied to evaluate the ability of EFWD to predict inter-twin disparity ≥ 25%, stillbirth, asphyxia and admission to a neonatal intensive unit (NICU). Chorionicity-stratified analysis was further performed.

RESULTS

Two hundred sixty-six monochorionic and 760 dichorionic twin pregnancies were analysed. The percentage errors in foetal weight estimations were 7-13%, whereas percentage errors in the estimation of inter-twin disparity were nearly 100%. Among eight formulas, Hadlock1 performed best, with a detectable rate of 65% and a false positive rate of 5% when predicting inter-twin disparity ≥ 25%. EFWD ≥ 22% was strongly associated with stillbirth (OR = 4.17, 95% CI 1.40-12.40) and NICU admission (OR = 3.48, 95% CI 2.03-5.97) after adjustment for gestational age, parity and abnormal umbilical systolic/diastolic ratio. Ultrasound had better predictive ability in monochorionic twins.

CONCLUSION

The predictive value of ultrasound for isolated inter-twin discordance and adverse perinatal outcomes was limited, which was possibly due to the magnifying of systematic errors in the disparity estimation compared with weight estimation. Despite this, abnormal biometry was an independent contributor for the poor prognosis of neonates.

A modified model can improve the accuracy of foetal weight estimation by magnetic resonance imaging

PURPOSE

To determine whether birth weight can be reliably estimated using three-dimensional (3D) magnetic resonance imaging (MRI) foetal body volume at term.

METHOD

Foetuses between 37⁺⁵ weeks and 41 weeks of gestation were delivered within 7 days after MRI and ultrasound (US) examinations. 3D foetal models were reconstructed from MRI data, and body volume was calculated. The MRI-based weight estimations were calculated using the Baker equation and the modified Baker equation with a higher density coefficient. The US-based weight estimations were determined using the formula by Hadlock. Estimations based on MRI and US were compared with the birth weights.

RESULTS

Among 22 foetuses that underwent both US and MRI evaluations within 48 h before labour, the mean random errors for the estimated weight based on US, the Baker equation and the modified Baker equation were 6.5%, 4.8%, and 4.8%, respectively, and these methods correctly estimated the weights of 77.3%, 86.4% and 100% of the foetuses to within 10% of the actual birth weight. The weights of 95.5% of the foetuses were underestimated by the Baker equation. Similar findings were observed among 103 estimations based on both US and MRI within 7 days before delivery. The mean relative error of the MRI-determined estimate of foetal weight using the modified Baker equation was not significantly associated with foetal sex, birth weight, gestational age at MRI examination, the MRI-to-delivery interval or the type of MRI scanner.

CONCLUSION

A modified Baker equation with a high-density coefficient can improve the accuracy of foetal weight estimation based on 3D MRI foetal volume at term, and its accuracy was not significantly affected by foetal characteristics or the type of MRI scanner among births occurring within 7 days after examinations.

Foetal weight prediction models at a given gestational age in the absence of ultrasound facilities: application in Indonesia

BACKGROUND

Birth weight is one of the most important indicators of neonatal survival. A reliable estimate of foetal weight at different stages of pregnancy would facilitate intervention plans for medical practitioners to prevent the risk of low birth weight delivery. This study has developed reliable models to more accurately predict estimated foetal weight at a given gestation age in the absence of ultrasound facilities.

METHODS

A primary health care centre was involved in collecting retrospective non-identified Indonesian data. The best subset model selection criteria, coefficient of determination, standard deviation, variance inflation factor, Mallows Cp, and diagnostic tests of residuals were deployed to select the most significant independent variables. Simple and multivariate linear regressions were used to develop the proposed models. The efficacy of models for predicting foetal weight at a given gestational age was assessed using multi-prediction accuracy measures.

RESULTS

Four weight prediction models based on fundal height and its combinations with gestational age (between 32 and 41 weeks) and ultrasonic estimates of foetal head circumference and foetal abdominal circumference have been developed. Multiple comparison criteria show that the proposed models were more accurate than the existing models (mean prediction errors between - 0.2 and 2.4 g and median absolute percentage errors between 4.1 and 4.2%) in predicting foetal weight at a given gestational age (between 35 and 41 weeks).

CONCLUSIONS

This research has developed models to more accurately predict estimated foetal weight at a given gestational age in the absence of ultrasound machines and trained ultra-sonographers. The efficacy of the models was assessed using retrospective data. The results show that the proposed models produced less error than the existing clinical and ultrasonic models. This research has resulted in the development of models where ultrasound facilities do not exist, to predict the estimated foetal weight at varying gestational age. This would promote the development of foetal inter growth charts, which are currently unavailable in Indonesian primary health care systems. Consistent monitoring of foetal growth would alleviate the risk of having inter growth abnormalities, such as low birth weight that is the most leading factor of neonatal mortality.

A New Model for Birth Weight Prediction Using 2- and 3-Dimensional Ultrasonography by Principal Component Analysis: A Chinese Population Study

OBJECTIVES

To establish a new model for birth weight prediction using 2- and 3-dimensional ultrasonography (US) by principal component analysis (PCA).

METHODS

Two- and 3-dimensional US was prospectively performed in women with normal singleton pregnancies within 7 days before delivery (37-41 weeks' gestation). The participants were divided into a development group (n = 600) and a validation group (n = 597). Principal component analysis and stepwise linear regression analysis were used to develop a new prediction model. The new model's accuracy in predicting fetal birth weight was confirmed by the validation group through comparisons with previously published formulas.

RESULTS

A total of 1197 cases were recruited in this study. All interclass and intraclass correlation coefficients of US measurements were greater than 0.75. Two principal components (PCs) were considered primary in determining estimated fetal birth weight, which were derived from 9 US measurements. Stepwise linear regression analysis showed a positive association between birth weight and PC1 and PC2. In the development group, our model had a small mean percentage error (mean ± SD, 3.661% ± 3.161%). At least a 47.558% decrease in the mean percentage error and a 57.421% decrease in the standard deviation of the new model compared with previously published formulas were noted. The results were similar to those in the validation group, and the new model covered 100% of birth weights within 10% of actual birth weights.

CONCLUSIONS

The birth weight prediction model based on 2- and 3-dimensional US by PCA could help improve the precision of estimated fetal birth weight.

Sonographic prediction of macrosomia in pregnancies complicated by maternal diabetes: finding the best formula

PURPOSE

To evaluate the best performing formula for macrosomia prediction in pregnancies complicated by diabetes.

METHODS

A retrospective analysis was performed of 1060 sonographic fetal biometrical measurements performed within 7 days of delivery in term pregnancies (37-42 gestational weeks) complicated by diabetes. Sonographic prediction of macrosomia (≥ 4000, ≥ 4250, and ≥ 4500 g) was evaluated utilizing ten previously published formulas by: (1) calculating for each macrosomia threshold the sensitivity, specificity, positive and negative predictive value, and ± likelihood ratio for macrosomia prediction; (2) comparing the systematic and random error and the proportion of estimates < 10% of birth weights between macrosomic and non-macrosomic neonates. Best performing formula was determined based on Euclidean distance.

RESULTS

97 (9.2%) macrosomic neonates (> 4000 g) were included. Median birth weight was 3380 (1866-3998) g for non-macrosomic and 4198 (4000-5180) g for macrosomic neonates. Higher macrosomia cutoff was associated with higher specificity and lower sensitivity. We found a considerable variation between formulas in different accuracy parameters. Hadlock's formula (1985), based on abdominal circumference, femur length, head circumference and biparietal diameter, had the shortest Euclidean distance, reflecting the highest accuracy.

CONCLUSION

Prediction of macrosomia among women with diabetes differs significantly between formulas. In our cohort, the best performing formula for macrosomia prediction was Hadlock's formula (1985).

Disadvantages of a weight estimation formula for macrosomic fetuses: the Hart formula from a clinical perspective

Purpose

Sonographic fetal weight (FW) estimation to detect macrosomic fetuses is an essential part of everyday routine work in obstetrics departments. Most of the commonly used weight estimation formulas underestimate FW when the actual birth weight (BW) exceeds 4000 g. One of the best-established weight estimation formulas is the Hadlock formula. In an effort to improve the detection rates of macrosomic infants, Hart et al. published a specially designed formula including maternal weight at booking. The usefulness of the Hart formula was tested.

Methods

Retrospective study of 3304 singleton pregnancies, birth weight ≥ 3500 g. The accuracy of the Hadlock and Hart formula were tested. A subgroup analysis examined the influence of the maternal weight. The Chi-squared test and one-way analysis of variation were carried out. For all analyses, p < 0.05 was considered statistically significant.

Results

The overall percentages of births falling within ± 5% and ± 10% of the BW using the Hadlock formula were 27% and 53%, respectively. Using the Hart formula, 24% and 54% were identified within these levels. With the Hart formula, 94% of all weight estimations fall within 4200 g ± 5% and nearly 100% fall within 4200 g ± 10%.

Conclusions

Applying the Hart formula results in an overestimation of fetal weight in neonates with a birth weight < 4000 g and fails to identify high-risk fetuses. We, therefore, do not consider Hart’s formula to be of clinical relevance.

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.

Prospective assessment of INTERGROWTH-21st and World Health Organization estimated fetal weight reference curves

OBJECTIVES

To assess the suitability of the new INTERGROWTH-21^st and World Health Organization (WHO) estimated fetal weight (EFW) references in a Southern Chinese population. A secondary aim was to determine the accuracy of EFW by assessing the difference between EFW and actual birth weight.

METHODS

This was a prospective cross-sectional cohort study. Viable singleton pregnancies at 11-13 weeks' gestation were recruited to undergo a single standardized fetal biometric scan after 20 weeks. The gestational age at which the scan was performed was allocated randomly at the time of recruitment. EFW was predicted using both the Hadlock and INTERGROWTH-21^st weight estimation model formulae. Population-specific EFW references were constructed. Z-scores were used to compare these references against the INTERGROWTH-21^st and WHO international size references. Gestational-age-adjusted projection was used to assess the difference between EFW on the day of delivery and birth weight for fetuses having biometry scans ≥ 34 weeks.

RESULTS

Fetuses of 970 participants had biometry scans. The median number of scans per gestational week was 48 (interquartile range, 43-53). Z-score comparison indicated that the WHO 10^th , 50^th and 90^th centiles of the EFW reference were consistently higher than the corresponding local centiles, whilst the INTERGROWTH-21^st 10^th centile was lower. Fewer than 2% of fetuses scanned at or after 34 weeks would be considered as potentially large-for-gestational age, irrespective of which model was used to predict weight. Adopting the WHO international reference would result in approximately one in six fetuses being regarded as potentially small-for-gestational age, 50% more than the number determined using a population-specific reference. Systematic errors of extrapolated EFW were similar, ranging from 5.5% to 7.4%.

CONCLUSIONS

Centers seeking to use new references, such as the INTERGROWTH-21^st and/or WHO international references, as a means of determining whether a fetus is small- or large-for-gestational age, would be advised to assess the suitability of these references within their own population using standardized methodology. Copyright © 2017 ISUOG. Published by John Wiley & Sons Ltd.

Estimating Gestational Age With Sonography: Regression-Derived Formula Versus the Fetal Biometric Average

OBJECTIVES

To compare the accuracy of a new regression-derived formula developed from the National Fetal Growth Studies data to the common alternative method that uses the average of the gestational ages (GAs) calculated for each fetal biometric measurement (biparietal diameter, head circumference, abdominal circumference, and femur length).

METHODS

This retrospective cross-sectional study identified nonanomalous singleton pregnancies that had a crown-rump length plus at least 1 additional sonographic examination with complete fetal biometric measurements. With the use of the crown-rump length to establish the referent estimated date of delivery, each method's (National Institute of Child Health and Human Development regression versus Hadlock average [Radiology 1984; 152:497-501]), error at every examination was computed. Error, defined as the difference between the crown-rump length-derived GA and each method's predicted GA (weeks), was compared in 3 GA intervals: 1 (14 weeks-20 weeks 6 days), 2 (21 weeks-28 weeks 6 days), and 3 (≥29 weeks). In addition, the proportion of each method's examinations that had errors outside prespecified (±) day ranges was computed by using odds ratios.

RESULTS

A total of 16,904 sonograms were identified. The overall and prespecified GA range subset mean errors were significantly smaller for the regression compared to the average (P < .01), and the regression had significantly lower odds of observing examinations outside the specified range of error in GA intervals 2 (odds ratio, 1.15; 95% confidence interval, 1.01-1.31) and 3 (odds ratio, 1.24; 95% confidence interval, 1.17-1.32) than the average method.

CONCLUSIONS

In a contemporary unselected population of women dated by a crown-rump length-derived GA, the National Institute of Child Health and Human Development regression formula produced fewer estimates outside a prespecified margin of error than the commonly used Hadlock average; the differences were most pronounced for GA estimates at 29 weeks and later.

Inter-observer variability in fetal biometric measurements

OBJECTIVE

To evaluate inter-observer variability and reproducibility of ultrasound measurements for fetal biometric parameters.

MATERIALS AND METHODS

A prospective cohort study was implemented in two tertiary care hospitals in Amman, Jordan; Prince Hamza Hospital and Albashir Hospital. 192 women with a singleton pregnancy at a gestational age of 18-36 weeks were the participants in the study. Transabdominal scans for fetal biometric parameter measurement were performed on study participants from the period of November 2014 to March 2015. Women who agreed to participate in the study were administered two ultrasound scans for head circumference, abdominal circumference and femur length. The correlation coefficient was calculated. Bland-Altman plots were used to analyze the degree of measurement agreement between observers. Limits of agreement ± 2 SD for the differences in fetal biometry measurements in proportions of the mean of the measurements were derived. Main outcome measures examine the reproducibility of fetal biometric measurements by different observers.

RESULTS

High inter-observer inter-class correlation coefficient (ICC) was found for femur length (0.990) and abdominal circumference (0.996) where Bland-Altman plots showed high degrees of agreement. The highest degrees of agreement were noted in the measurement of abdominal circumference followed by head circumference. The lowest degree of agreement was found for femur length measurement. We used a paired-sample t-test and found that the mean difference between duplicate measurements was not significant (P > 0.05).

CONCLUSION

Biometric fetal parameter measurements may be reproducible by different operators in the clinical setting with similar results. Fetal head circumference, abdominal circumference and femur length were highly reproducible. Large organized studies are needed to ensure accurate fetal measurements due to the important clinical implications of inaccurate measurements.

Predicting birth weight in fetuses with gastroschisis

OBJECTIVE

To determine the accuracy of commonly utilized ultrasound formulas for estimating birth weight (BW) in fetuses with gastroschisis.

STUDY DESIGN

A retrospective review was conducted of all inborn pregnancies with gastroschisis within the five institutions of the University of California Fetal Consortium (UCfC) between 2007 and 2012. Infants delivered at ⩾28 weeks who had an ultrasound within 21 days before delivery were included. Prediction of BW was evaluated for each of the five ultrasound formulas: Hadlock 1 (abdominal circumference (AC), biparietal diameter (BPD), femur length (FL) and head circumference (HC)) and Hadlock 2 (AC, BPD and FL), Shepard (AC and BPD), Honarvar (FL) and Siemer (BPD, occipitofrontal diameter (OFD), and FL) using Pearson's correlation, mean difference and percent error and Bland-Altman analysis. Sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) for the ultrasound diagnosis of intrauterine growth restriction (IUGR) were assessed.

RESULTS

We identified 191 neonates born with gastroschisis within the UCfC, with 111 neonates meeting the inclusion criteria. The mean gestational age at delivery was 36.3±1.7 weeks and the mean BW was 2448±460 g. Hadlock (1) formula was found to have the best correlation (r=0.81), the lowest mean difference (8±306 g) and the lowest mean percent error (1.4±13%). The Honarvar and Siemer formulas performed significantly worse when compared with Hadlock 1, with a 13.7% (P<0.001) and 3.9% (P=0.03) difference, respectively, between estimated and actual BW. This was supported by Bland-Altman plots. For Hadlock 1 and 2, sensitivity was 80% with a NPV of 91%.

CONCLUSION

The widely used Hadlock (1) and (2) formulas provided the best estimated BW in infants with gastroschisis despite its inclusion of abdominal circumference. Furthermore, this formula performs well with diagnosis of IUGR.

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.

Five-dimensional long bones biometry for estimation of femur length and fetal weight at term compared to two-dimensional ultrasound: a pilot study

BACKGROUND/OBJECTIVE

This study aimed to evaluate accuracy of five-dimensional long bones (5D LB) compared to two-dimensional ultrasound (2DUS) biometry to predict fetal weight among normal term women.

METHODS

Fifty six normal term women were recruited at Ain Shams Maternity Hospital, Egypt from 14 May to 30 November 2015. Fetal weight was estimated by Hadlock's IV formula using 2DUS and 5D LB. Estimated fetal weights (EFW) by 2DUS and 5D LB were compared with actual birth weights (ABW).

RESULTS

Mean femur length (FL) was 7.07 ± 0.73 cm and 6.74 ± 0.67 cm by 2DUS and 5D LB (p = .02). EFW was 3309.86 ± 463.06 g by 2DUS and 3205.46 ± 447.85 g by 5D LB (p = .25). No statistical difference was observed between ABW and EFW by 2DUS (p = .7) or 5D LB (p = .45). Positive correlation was found between EFW by 2DUS, 5D LB, and ABW (r = 0.67 and 0.7; p < .001). There was strong agreement between FL measured by 2DUS and 5D LB (ICC = 0.78), and perfect agreement between EFW by 2DUS and EFW by 5D LB (ICC = 0.918). 2DUS and 5D LB showed mean absolute percentage error for EFW of 10 ± 7% and 8 ± 7% compared to ABW (p = .15).

CONCLUSIONS

2DUS and 5D LB had same accuracy for fetal weight estimation at normal term pregnancy.

Practice Bulletin No. 173: Fetal Macrosomia

Suspected fetal macrosomia is encountered commonly in obstetric practice. As birth weight increases, the likelihood of labor abnormalities, shoulder dystocia, birth trauma, and permanent injury to the neonate increases. The purpose of this document is to quantify those risks, address the accuracy and limitations of methods for estimating fetal weight, and suggest clinical management for a pregnancy with suspected fetal macrosomia.

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.