Sonographic Fetal Weight Estimation Research Articles

Accuracy of sonographic fetal weight estimation: a matter of presentation

To assess the accuracy of sonographic weight estimation for fetuses in breech presentation, and to determine whether certain sonographic models perform better than others in cases of breech presentation. This was a retrospective cohort study of all sonographic weight estimations of fetuses in breech presentation performed within 3 days prior to delivery (n = 165). The accuracy of weight estimation was evaluated using eight sonographic models and was compared with a control group of fetuses in vertex presentation matched to the study group by birth weight and fetal gender (n = 165). After exclusion of a model based on femur diaphysis length alone, which was found to be highly inaccurate, the systematic error for fetuses in breech presentation was smaller than that observed for fetuses in vertex presentation (mean of all models - 0.14% vs. 2.0%, P = 0.01). The random error was higher in cases of breech presentation (9.4-13.2% vs. 7.5-8.9%, P < 0.05), and was lower for models that are based on three to four biometric indices (9.4-9.5%) compared with models that incorporate one to two biometric indices (10.8-13.6%, P < 0.05). Overall, the higher random error outweighed the decrease in the systematic error, as reflected by the lower fraction of weight estimations within 10% of birth weight among fetuses in breech presentation. Models based on three to four biometric indices were more accurate in detecting the weight thresholds beyond which a trial of vaginal delivery is usually not recommended. Sonographic weight estimation appears to be less accurate for fetuses in breech presentation, principally because of a larger random error. The use of sonographic models that are based on three to four biometric indices, training aimed at improving measurement in breech fetuses and the development of sonographic models derived from fetuses in breech presentation, may improve the accuracy of weight estimation in these cases.

Accuracy of sonographic weight estimation as a function of fetal sex

To determine whether the accuracy of sonographic fetal weight estimation is related to fetal sex. The accuracy of sonographic fetal weight estimation was compared between male and female fetuses using 3672 sonographic weight estimations performed within 3 days prior to delivery. Fetal weight was estimated using eight regression models that are based on different combinations of the following biometric parameters: abdominal circumference (AC), femur diaphysis length (FL), biparietal diameter (BPD) and head circumference (HC). In seven out of the eight models tested, the presence of a male fetus was associated with a significantly lower systematic error compared with a female fetus (-0.2 to 2.1% vs. 1.3 to 6%, P<0.001). On multivariate analysis, fetal sex was independently associated with sonographic accuracy so that the likelihood of a weight estimation within 10% of birth weight was 30% higher for male fetuses compared with female fetuses. The biometric parameters that contributed most to these sex-related differences were FL and AC, while models that included HC were associated with the lowest differences in the systematic error between male fetuses and female fetuses. For most models, the random error and correlation between estimated weight and birth weight were not affected by fetal sex (8.1-12.8% vs. 8.2-13.6%, and 0.856-0.944 vs. 0.842-0.944, respectively). Sonographic estimation of fetal weight is more accurate for male fetuses than for female fetuses. The use of sex-specific models may improve the accuracy of fetal weight estimation for female fetuses.

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

To compare the accuracy of 21 sonographic fetal weight-estimation models and abdominal circumference (AC) as a single measure for the prediction of fetal macrosomia (> 4000 g) using either fixed or optimal model-specific thresholds. A total of 4765 sonographic weight estimations performed within 3 days prior to delivery were analyzed. The predictive accuracy of 21 published sonographic fetal weight-estimation models was calculated using three different thresholds: a fixed threshold of 4000 g; a model-specific threshold obtained from the inflexion point of the receiver-operating characteristics (ROC) curve; and a model-specific threshold associated with the highest overall accuracy. Cluster analysis was used to determine whether a certain combination of fetal biometric indices is associated with a higher predictive accuracy than others. For a fixed threshold of > 4000 g, there was considerable variation among the models in sensitivity (range, 13.6-98.5%) and specificity (range, 63.6-99.8%) for fetal macrosomia. Use of the threshold derived from the inflexion point of the ROC curve decreased the intermodel variation to a minimum (sensitivity, 84.4-91.4%; and specificity, 79.5-86.3%). Even when this optimal model-specific threshold was applied, models based on three to four biometric indices were more accurate than were models based on only two biometric indices or on AC as a single measure (P=0.03). Sonographic fetal weight-estimation models based on three to four biometric indices appear to be more accurate than are models based on two indices or on AC as a single measure, for the diagnosis of macrosomia. In these cases, the use of an optimal, model-specific threshold is associated with a higher degree of accuracy than is the uniform use of a fixed threshold of an estimated weight of > 4000 g.

700: The accuracy of sonographic fetal weight estimation in cases of breech presentation-how accurate we are?

700: The accuracy of sonographic fetal weight estimation in cases of breech presentation-how accurate we are?

Accuracy of sonographic fetal weight estimation of fetuses with a birth weight of 1500 g or less

Objective To compare 35 commonly used formulae for small and average sized fetuses on their accuracy in estimating the birth weight in fetuses of 1500 g or less. Study design For this retrospective study a database search was performed for all singleton pregnancies without structural or chromosomal defects and with a birth weight of 1500 g or less where the last ultrasound examination was performed within seven days before delivery. Percentage error and absolute percentage error were calculated based on 35 different weight estimation formulae. Multiple regression analysis was used to determine the significant contributors to the absolute percentage error. Results One hundred and ninety-three cases fulfilled the inclusion criteria. The median birth weight was 990 g. The percentage error ranged between −15.2% (underestimation with the Merz I formula) and 37.4% (overestimation with the Jordaan formula) and the respective standard deviations between 10.5% (Mielke I) and 54.0% (Schillinger), respectively. The absolute percentage error was between 8.5% and 37.6%. The most accurate weight estimation was achieved with the formula from Mielke (percentage error 1.8% and absolute percentage error 8.5%). Multiple regression analysis showed that significant contributors to the percentage error of the Mielke formula were biparietal diameter (OR = −0.206, p = 0.045), occipitofrontal diameter (OR = 0.765, p < 0.0001), abdominal circumference (OR = −2.953, p < 0.0001), femur length (OR = −0.903, p < 0.0001), head to abdomen ratio (OR = −1.080, p < 0.0001) and fetal weight (OR = 2.847, p < 0.0001). Conclusion When estimating fetal weight in fetuses weighing 1500 g or less, one has to be aware of the great differences in accuracy among the formulae.

Evaluation of six commonly used formulae for sonographic estimation of fetal weight in a Sri Lankan population

Objective: To compare six commonly used formulae (Shepard, Campbell, Hadlock I, II, III, and IV) for estimation of fetal weight in Sri Lankan population. Methods: A descriptive cross-sectional study conducted at Ward 9, Sri Jayewardenepura General Hospital, Kotte, Sri Lanka from the October to December 2007.The study included 86 singleton pregnancies. The fetal biometry - biparietal diameter (BPD), head circumference (HC), abdominal circumference (AC), femur length (FL) - ultrasonically measured on the previous day of planned delivery, actual birth weights (ABW) taken within 30 minutes of delivery. Estimated fetal weight (EFW) from each equation calculated using basic biometric values for estimation of fetal weight. Statistical analysis done using Karl Pierson correlation. Results: The highest positive correlation between the ABW and the EFW was seen in the Hadlock IV (r =0.836). According to the area under the curve for each ROC curve Hadlock IV equation has the highest (0.849). For fetuses less than 2.5 kg Hadlock IV has the highest sensitivity (75%). All the equations have the high specificity which ranges from93.6h to 100%. In fetuses more than 3.5 kg the Shepard has the highest sensitivity (90%). The specificity is highest (97.4%) in Hadlock IV. Even though the Hadlock IV is the best formula identified in our study to predict babies less than 2.5 kg out of whole population, it is not the best for prediction of a baby larger than 3.5 kg (Hadlock IV sensitivity 40%) compared to Hadlock I (sensitivity 80% and specificity 89.5%) which is the best formula to predict a baby more than 3.5 kg. Conclusion: All formulae have adequate accuracy for estimating fetal weight in the population tested, Hadlock IV has the best accuracy. Key words: Fetal weight; obstertrics sonography. DOI: 10.4038/sljog.v31i1.1735 Sri Lanka Journal of Obstetrics and Gynaecology 2009; 31 : 20-33

Early fetal growth: concepts and pitfalls

Early fetal growth: concepts and pitfalls

Continuous independent quality control for fetal ultrasound biometry provided by the cumulative summation technique

To apply the cumulative summation (CUSUM) technique for an evaluation of the learning process of sonographic fetal weight estimation at term in combination with the z-scores of biometry determinants and to assess the time of appearance and sources of errors. Learning curve (LC-CUSUM) and double CUSUM charts for systematic error detection based on absolute and signed mean percentage error were generated to retrospectively estimate the longitudinal accuracy of sonographic fetal weight estimation conducted by three trainees and one experienced examiner. For LC-CUSUM analysis an examination was considered to be a failure when there was an absolute error in birth weight estimation >/= 15%. Fetal biometry measurements (head circumference, abdominal circumference (AC) and femur length (FL)) from 227 routine ultrasound scans of one examiner were separately transformed into z-scores and double CUSUM charts were generated to assess the systematic errors for each determinant. The LC-CUSUM charts revealed that different numbers of scans are required for different examiners to achieve competence in estimating birth weight. AC and FL deviated most significantly from expected values (P < 0.05). The double CUSUM charts revealed exact periods of systematic errors in the measurement of biometry determinants, clearly reflecting errors of fetal weight estimation. The use of CUSUM techniques in the analysis of sonographic data allows observation of the development of an examiner's skill and maintenance of competence. The CUSUM technique not only allows the reasons for impaired fetal weight estimation to be revealed but also allows determination of the exact time when inaccurate measurements start to occur. We suggest that CUSUM charts should be implemented in routine clinical practice as a measure of objective quality evaluation of sonographic fetal biometry.

331: Sonographic suspicion of macrosomia effecting mode of delivery

To determine if infants with sonographic suspicion for macrosomia have improved outcomes over infants with birthweight (BW) >4kg and no antenatal sonographic suspicion for macrosomia. All infants suspected of having macrosomia based on ultrasound (estimated fetal weight (EFW) >4kg) and all singleton infants born with macrosomia (defined as BW >4kg) were identified in a large academic center in 2007. Of 5013 singleton deliveries, 81 infants (1.6%) had a sonographic EFW >4kg (Susp). 374 infants (7.5%) had BW>4kg (Act) and of these, 328 were not suspected antenatally by ultrasound (Unsusp). Susp had lower BW compared to Unsusp (4110±427 vs 4240±422 g, p<0.01), but higher rates of induction (41.9% vs 30.2%, p<0.05) and primary cesarean delivery (CD) (38.7% vs 25.9%, p<0.05). Susp and Unsusp had similar rates of NICU admission (2.5% vs 3.4%), shoulder dystocia (3.7% vs 4%), newborn hospital stay (4.1±11.5 vs 3.1 ±2.5 d), and similar gestational age at birth (39.5±5 vs 39.4±1 wk). All groups had similar rates of diabetes. Subset of Susp with BW>4kg (n=46, 56.8%) were heavier (4366 ±352 vs 4240 ±197 g, p<0.001) and had higher primary CD (47.8 vs 25.9%, p<0.01) compared to Unsusp, but similar rates of NICU admission (2.2 vs 3.4%), shoulder dystocia (2.2 vs 4.0%), and neonatal hospital stay (2.9±0.9 vs 3.1±2.5 d). Susp with BW<4kg (n=35, 43.2%) had lower BW (3772±221 vs 4240±197g, p<0.001), lower ponderal index (3.2±0.6 vs 3.7 ±0.5, p<0.03), higher induction rates (51.4% vs 30.2%, p<0.01), but similar rates of primary CD (30% vs 18.8%), NICU admission (2.9% vs 3.4%), shoulder dystocia (5.7% vs 4.0%), and hosptial stay (5.6±17 vs 3.1±2.5 d) compared to Unsusp. Suspicion of macrosomia based on sonographic EFW may have greater impact on management then clinical EFW and lead to higher rates of primary CD and induction of labor without improving immediate neonatal outcome.

Fetal Weight Estimation by 2D and 3D Ultrasound: Comparison of Six Formulas

To evaluate and compare the accuracy of different formulas to estimate fetal weight using 2D and 3D ultrasound. We performed a prospective study on unselected singleton pregnancies. All scanned fetuses delivered within 7 days in absence of structural and chromosomal abnormalities were included. The fetal weight was calculated using the 3D Schild, Chang, Liang and 2D Hansmann, Merz and Hadlock formulas. Absolute and mean deviations of estimated fetal weight were calculated. Of 249 scanned fetuses 200 that fulfilled the criteria were included. Birth weights ranged between 535 and 5020 g. The highest correlation between estimated fetal and birth weight was achieved by applying Schild's equation, and the absolute percentage error was 5.6%. The corresponding values for 2D Hansmann, Merz and four-parametric Hadlock formulas were 7.5%, 7.9%, and 9.2%, respectively, while these were 13.1% and 30.7% for Liang's and Chang's 3D equations. Using the Schild formula, a deviation from birth weight below 10 % was achieved in 80 % of fetuses, with Hansmann's in 73.5% and with Merz in 72.5%, while this parameter was much lower in the remaining equations. The best option with the highest accuracy for sonographic fetal weight estimation was the 3D Schild equation followed by the 2D Hansmann and Merz formulas. Published data of the accuracy could be reproduced with the exception of the "Asian" 3D equations in our European population. The limited improvement in weight agreement using the 3D technique compared to the 2D technique may be outweighed by the time consumption.

Environmental rather than genetic fetal overgrowth: defining the difference and hints for diagnosis and management

Environmental rather than genetic fetal overgrowth: defining the difference and hints for diagnosis and management

Effect of Increased Body Mass Index on the Accuracy of Estimated Fetal Weight by Sonography in Twins

The purpose of this study was to determine whether increasing body mass index (BMI) decreases the accuracy of sonographic estimations of fetal weight in twin gestations. A chart review was conducted, in which 361 charts of patients with twin gestations over a 2-year period were reviewed. A total of 194 patients had sonographic examinations for fetal weight within 6 days of delivery and were included in the analysis. The difference between the sonographically estimated fetal weight was compared with the actual birth weight for each twin and stratified for the patient's BMI. There was a significant increasing trend in mean absolute percent errors with increasing BMIs in both twins (P< .05). The mean absolute percent errors for twin A were 6% for patients with a BMI of less than 25 and 9% for those with a BMI of greater than 30. The mean absolute percent errors for twin B were 6.7% for patients with a BMI of less than 25 and almost 11.7% for those with a BMI of greater than 30. There was a significantly increasing trend in mean absolute differences in grams for both twins with increasing gestational age, with almost a 4-fold increase from less than 28 weeks to greater than 36 weeks in both twins (P< .05). Increasing maternal obesity decreases the accuracy of sonographically determined fetal weight in twin gestations, particularly for twin B.

Sonographic fetal weight estimation in prolonged pregnancy: comparative study of two‐ and three‐dimensional methods

To compare two-dimensional (2D) and three-dimensional (3D) ultrasound techniques, including volumetry of fetal thigh, for fetal weight (FW) estimation in prolonged pregnancy, and to develop a new FW estimation formula. This prospective comparative study initially included 176 pregnant women. FW estimation was performed at >or= 287 days of gestation within <or= 4 days of delivery. Fetal head, abdomen and femur were measured using 2D ultrasound techniques, and fetal thigh volume was estimated using 3D techniques. The formula of Persson and Weldner (2D) was compared with two 3D formulae published by Lee and colleagues. In a subgroup of 63 fetuses, volumetry of the abdomen was performed and a new formula was developed; this formula was tested prospectively, along with the previously published formulae, on a further 50 women (Test Group). In the initial group of 176 pregnancies, the SD of the mean percentage error (MPE) was 6.3% for both the 2D Persson and Weldner formula and for the better performing 3D formula of Lee et al., but the MPE of this Lee formula differed significantly from zero. Significantly more FW estimations were within +/- 10% of the birth weight when the 2D formula was used than when the 3D formulae were applied. The new formula gave a SD of MPE of 5.6% when applied to the data from which it was derived. In the Test Group, the SD of MPE was similar for the 2D formula, the second formula of Lee et al. and the new formula, with values of 7.0, 7.0 and 7.1, respectively, but only the Persson and Weldner formula showed a MPE that did not differ significantly from zero. FW in prolonged pregnancies can be estimated using 2D sonography with the same accuracy as with 3D sonography. 3D ultrasound techniques require technically advanced and expensive equipment, special operator training and skills, and are time consuming. It does not seem reasonable to abandon the 2D ultrasound methods in favor of 3D ultrasound imaging for FW estimation.

481: Sonographic estimation of fetal weight in breech presentation: Are current equations equally as accurate?

Although several ultrasonographic fetal biometric equations have been created for the estimation of fetal weight, these have typically been created using fetuses in cephalic presentation. The optimal algorithm for the estimation of fetal weight among breech fetuses has not yet been determined.

Clinical estimation of fetal weight and the Hawthorne effect

Objective The Hawthorne effect refers to improvement in performance solely due to the subject's knowledge that he or she is being studied. We sought to determine if an obstetrician's clinical estimation of fetal weight (EFW) is influenced by the Hawthorne effect seen in some clinical trials. Study design We compared obstetricians’ clinical EFW's obtained during a study period to those obtained prior to the study period in one institution. We included any patient presenting at ≥37 weeks gestation. We excluded multiple pregnancies and patients with a recent sonographic EFW. Results There was no difference in regards to the proportion of EFW's within 10% of the birthweight (67.9% vs. 68.5%, p = .91), the mean absolute difference of EFW-birthweight (282 ± 227 g vs. 285 ± 232 g, p = .88), or the mean absolute percent error (8.5 ± 7.4% vs. 8.6 ± 7.2%, p = .96). We also could not find any Hawthorne effect when we excluded resident physicians’ EFW's and when we analyzed the subgroup of newborns with a birth weight ≥4000 g. Conclusion An obstetrician's knowledge that he or she is being studied is unlikely to improve clinical EFW accuracy. Published clinical EFW accuracies are likely to be similar to those obtained in clinical practice.

Detection of Fetal Growth Restriction with Preterm Severe Preeclampsia: Experience at Two Tertiary Centers

Our objective was to determine if sonographic estimate of fetal weight (SEFW) can identify fetal growth restriction (FGR; birthweight < 10% for gestational age [GA]) among patients with preterm (28 to 32 weeks) severe preeclampsia (P SPE). At two centers, all singletons with reliable GA, P SPE, and SEFW within 3 weeks of birth were identified retrospectively. Intrauterine growth restriction was SEFW < or = 10% for GA. Likelihood ratio (LR) and guidelines by an Evidence-Based Medicine Working Group were used. At the two centers, IUGR was suspected in 20% (4 of 20) and 28% (5 of 18) of P SPE, and FGR was noted in 35% and 44%. At one center, suspected intrauterine growth restriction (IUGR) was associated with actual FGR in 50% of the cases and at center II, in 80%. The LR for IUGR to identify FGR was 3.0. We concluded that SEFW is not a useful diagnostic test in identifying FGR among patients with preterm SPE.

Estimation of fetal weight by measurement of fetal thigh soft‐tissue thickness in the late third trimester

The accuracy of current formulae for the sonographic estimation of fetal weight (EFW) is compromised by significant intra- and interobserver variability of biometrical measurements, particularly circumferences. The aim of this study was to assess the reliability of the linear measurement of mid-thigh soft-tissue thickness (STT) and to derive a novel formula for EFW. This was a prospective study involving 388 singleton uncomplicated pregnancies. There were three consecutive phases: (1) to verify the relationship between STT and birth weight, (2) to derive a novel formula for EFW using femur length and STT only, and (3) to test the accuracy of the new equation. Only the 290 patients who delivered within 48 h of measurement were considered for the analysis. A comparison with other formulae was performed. STT was significantly correlated with both abdominal circumference and birth weight (r(2) = 0.36 and 0.46, respectively; P < 0.001). Both intra- and interobserver variability were satisfactory (0.44 +/- 0.27 and 0.57 +/- 0.35 mm, respectively). The equation for EFW was developed using multiple stepwise regression analysis (EFW = - 1687.47 + (54.1 x femur length) + (76.68 x STT)) and tested prospectively on 69 patients. The new formula yielded results (r = 0.79) that were slightly better in accuracy than two other published equations, and had an absolute mean error of < 15% in 97% of cases. Our findings confirm the potential of the linear measurement of mid-thigh STT as a valuable parameter for the sonographic assessment of fetal growth and EFW. Our new equation is apparently at least as reliable as the most widely used formulae for EFW.

Analysis of Factors Influencing the Ultrasonic Fetal Weight Estimation

Objective: The aim of our study was the evaluation of sonographic fetal weight estimation taking into consideration 9 of the most important factors of influence on the precision of the estimation. Methods: We analyzed 820 singleton pregnancies from 22 to 42 weeks of gestational age. We evaluated 9 different factors that potentially influence the precision of sonographic weight estimation (time interval between estimation and delivery, experts vs. less experienced investigator, fetal gender, gestational age, fetal weight, maternal BMI, amniotic fluid index, presentation of the fetus, location of the placenta). Finally, we compared the results of the fetal weight estimation of the fetuses with poor scanning conditions to those presenting good scanning conditions. Results: Of the 9 evaluated factors that may influence accuracy of fetal weight estimation, only a short interval between sonographic weight estimation and delivery (0–7 vs. 8–14 days) had a statistically significant impact. Conclusion: Of all known factors of influence, only a time interval of more than 7 days between estimation and delivery had a negative impact on the estimation.

173: Sonographic fetal weight estimation: Which model is best?

It remains unclear which formula, of the many formulas available in the literature, is the most accurate in predicting birthweight.Thus, we aimed to compare the accuracy of 23 sonographic models for fetal weight estimation, and to determine whether the accuracy improves as more fetal biometric indices are included in the model.

P40.11: Fetal esophagus pathology: place of the pouch sign

and non-anomalous singleton fetuses with intact fetal membranes. Sonographic measurements included biparietal diameter (BPD), head circumference (HC), abdominal circumference (AC), femur length (FL), humerus length (HL), transcerebellar diameter (TCD), and sonographic estimated fetal weight (SEFW). Values of axial FNC and FNA were each calculated as the mean of three separate measurements. The 5th, 50th, and 95th centiles were estimated at each week of gestational age (GA) by least-squares regression for the mean and standard deviation (SD) of the FNC and FNA as functions of GA. R2 and associated P-values for the relationships between FNC, FNA and BPD, HC, AC, HL, FL, TCD and SEFW were calculated. Results: The study included 720 consecutive patients. All attempts at measurement were successful. Mean maternal age = 27.3 ± 6.6 years. Median gravidity = 3 (range 1–13), median parity = 1 (range 0–10). Mean FNC (cm) = −11.85 + 1.687× GA (weeks) −0.043 × GA + 0.0004951 × GA. SD = 3.15–0.3823 × GA + 0.01733 × GA − 0.0002179 × GA. Mean FNA (cm2) = 37.29–7.0 × GA + 0.4717 × GA − 0.01245 × GA + 0.0001222 × GA. SD = 7.08–0.9413 × GA + 0.04135 × GA − 0.0004829 × GA. FNC and FNA correlated significantly and strongly with BPD, HC, AC, HL, FL, TCD and SEFW. Conclusions: Current nomograms of axial FNC and FNA throughout gestation have been provided.