Inter-observer variability in fetal biometric measurements

Objective

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

The feasibility of using 5D CNS software in obtaining standard fetal head measurements from volumes acquired by three-dimensional ultrasonography: comparison with two-dimensional ultrasound

Objective: To evaluate the performance of a new software (5D CNS) developed to automatically recognize the axial planes of the fetal brain from three-dimensional volumes and to obtain the basic standard biometric measurements. The accuracy, reproducibility, and time required for analysis of 5D CNS were compared with that of two-dimensional (2D) ultrasound.

Methods: This was a prospective study of 120 uncomplicated singleton pregnancies undergoing routine second trimester examination. For every pregnancy standard biometric measurements including biparietal diameter, head circumference, distal lateral ventricle width, transverse cerebellar diameter and cisterna magna width were obtained using 2D ultrasound and three-dimensional (3D) ultrasound with 5D CNS software. Reliability and agreement of the two techniques were evaluated using intraclass correlation coefficients (ICCs) and proportionate Bland–Altman plots were constructed. The time necessary to complete the measurements with either technique was compared and intraobserver and interobserver agreements of measurements calculated.

Results: In 118/120 (98.3%), 5D CNS successfully reconstructed the axial diagnostic planes and calculated all the basic biometric head and brain measurements. The agreement between the two techniques was high for all the measurements considered (all ICCS?>?0.920). The time necessary to measure the biometric variables considered was significantly shorter with 5D CNS (54 versus 115?s, p?<?0.0001) than with 2D ultrasonography. No significant differences were found in 5D CNS repeated measurements obtained either by the same observer or by two independent observers.

Conclusion: 5D CNS software allows us to obtain reliable biometric measurements of the fetal brain and to reduce the examination time. Its application may improve work-flow efficiency in ultrasonographic practices     

First trimester dating by fetal heart rate assessment: a comparison with crown-rump length measurement

Objective: The purpose of this study was to determine whether fetal heart rate (FHR) can be used to date pregnancies in the early first trimester using the gold standard of crown-rump length (CRL) dating as a reference.

Methods: This single center study evaluated women undergoing obstetrical ultrasounds between 4.5 and 8.5 weeks. FHR and gestational age (GA) based on CRL were obtained. Linear regression analysis and a Bland–Altman plot were used to demonstrate the relationship between the two measurements. A further simplified version of the relationship between CRL and FHR that may be clinically useful was calculated.

Results: 176 patients were included in the study. The Pearson correlation coefficient was 0.95, indicating a strong correlation between the two dating methods. The Bland–Altman plot demonstrated agreement across GA tested. A simple arithmetic formula of GA(weeks)?=?FHR (beats per minute)/20 was calculated. 169/176 patients had <4 days discrepancy between FHR- and CRL-based dating using this formula.

Conclusion: We found that a simple formula based on FHR may accurately date early pregnancies. This method, if further validated, may represent an important tool for pregnancy dating.     

A novel reference chart and growth standard of fetal biometry in the Taiwanese population

ObjectiveThe purpose of this study was to establish a new reference chart and growth standards for fetal biometry in Taiwan.Materials and methods2047 singleton pregnancies were enrolled in this study with 15,813 fetal scans between 18 and 40 gestational weeks. A reference chart and normal range for fetal biparietal diameter (BPD), abdominal circumference (AC) and femur length (FL) was established by longitudinal quantile regression model. 330 women with comorbidities including gestational hypertension, preeclampsia and gestational diabetes were excluded and 1717 pregnant women were enrolled for the growth standard.ResultsThe new reference values were significantly larger across all gestational ages compared with the prior National Taiwan University reference chart in 1983. Compared with Intergrowth-21st, the BPD was larger at 18–23 weeks, the AC was larger at 18–24 weeks and the FL was larger at 18–36 weeks whereas they were all smaller at 29–40 weeks for the BPD, at 32–40 weeks for the AC and at 38–40 weeks for the FL. A quantile regression equation of biometry was established. BPD, AC, and FL had weekly growth of 2.5, 9.87 and 2.15 mm. Prepregnancy body weight, height, age, and gestational diabetes increased fetal size. Both gestational and chronic hypertension decreased fetal size.ConclusionTo promote maternal-fetal safety, a new reference chart and growth standard for fetal biometry is necessary to measure fetal growth.     

Spine length measurement in the first trimester of pregnancy

OBJECTIVES: The aim of the study was to evaluate spine length as an indicator of skeletal growth in the first trimester of pregnancy and to provide a nomogram of spine length at the end of the first trimester of pregnancy. METHODS: The study was carried out on 420 single pregnancies, at gestational ages ranging from 11 to 14 weeks, using high-resolution transabdominal echography. Biparietal diameter and crown-rump length (CRL) were measured to date the pregnancy. Using the same scanning plane used to measure CRL, the whole spine length in antero-dorsal position can be visualized as a double hyperechoic line from 10 weeks of gestation onwards. Spine length was measured three times by one observer and the mean of the three measurements was considered as definitive. Forty fetuses had multiple measurements for interobserver and intraobserver error analysis. RESULTS: Linear relationship between spine length, and gestational age, biparietal diameter and CRL were demonstrated. Spine length (millimetres) as a function of gestational age (days) was expressed by the regression equation: spine length = 1.09 x (gestational age in days) -60.56, with a determination coefficient of R(2) = 0.744. Spine length ranged from 21.5 mm at 11 weeks to 41.9 mm at 14 weeks. CONCLUSION: The data obtained showed that spine length increased progressively from the end of the first trimester to the beginning of the second. A high correlation between spine length, gestational age, biparietal diameter, and CRL was observed. Spine length measurement could therefore be considered a good indicator of fetal growth.     

Fetal cerebral ventricle volumetry: comparison between 3D ultrasound and magnetic resonance imaging in fetuses with ventriculomegaly

Objectives.?The aim of this study was to evaluate feasibility of fetal lateral ventricle (LV) volumetry in fetuses with ventriculomegaly and to compare measurements performed by 3D sonographic method virtual organ computer-aided analysis (VOCAL) with those obtained by magnetic resonance imaging (MRI).

Methods.?This cross-sectional study evaluated 30 fetuses with atrial width (AW) between 10 and 30?mm, from 20 to 36 gestational weeks. Fifty-nine ventricles were measured by two observers. Sonographic volumetric measurements using VOCAL 30° were performed with an ACCUVIX XQ machine (Medison, Korea) and MRI assessments with a Sonata system using ARGUS software (Siemens, Germany). Agreement between both techniques was assessed by intraclass correlation coefficient (ICC) calculation, and proportionate Bland–Altman plots were constructed.

Results.?A high degree of reliability was observed between VOCAL and MRI measurements (ICC 0.928, 95%CI [0.876;0.958]). Bland–Altman plots confirmed the high correlation (mean of differences: 1.62 cm³ and standard deviation:?±?8.41 cm³).

Conclusion.?Three-dimensional volumetry of fetal LVs by VOCAL method has good agreement with fetal MRI in fetuses with ventriculomegaly and may be used as an additional tool in patient counseling and prognosis prediction.     

First-trimester fetal limb biometry in Chinese population

OBJECTIVES: To establish reference ranges for fetal limb biometry obtained by transabdominal ultrasound examination at 12-14 weeks of gestation in Chinese women. METHODS: A total of 1489 normal singleton fetuses between 12(+0) and 14(+6) weeks of gestation were examined transabdominally by two experienced observers. The gestation was ascertained by measurement of fetal crown-rump length (CRL) or biparietal diameter (BPD) and head circumference (HC). The lengths of the humerus and femur were prospectively worked out. RESULTS: Gestation-specific reference ranges for limb measurements were calculated. The femur length (FL) (mean +/- SD) was 9.15 +/- 1.44 mm at 12-12(+6) weeks, 11.45 +/- 1.35 mm at 13-13(+6) weeks, and 13.64 +/- 1.60 mm at 14-14(+6) weeks; the corresponding humerus length (HL) (mean +/- SD) was 9.63 +/- 1.44 mm, 12.01 +/- 1.41 mm, 14.29 +/- 1.48 mm, respectively. CONCLUSIONS: There was a general increase in fetal limb biometry with gestation. Fetal limb length can be an early marker of early growth restriction as well as fetal skeletal dysplasia among women in the local population.     

Fetal echocardiography during routine first-trimester screening: a feasibility study in an unselected population

OBJECTIVE: To evaluate the feasibility of obtaining standard echocardiographic views of the fetal heart during routine first-trimester screening and construct reference ranges for cardiac biometry at 11 + 0 to 13 + 6 weeks of gestation. METHODS: A cross-sectional study of 584 fetuses in an unselected population. Viable pregnancies with a crown-rump length (CRL) of 41-78 mm were included. Echocardiography was performed by a single obstetrician using a 5 to 7.5 MHz vaginal transducer. The course and outcome of pregnancies were recorded and information on the babies was obtained in all cases. RESULTS: A completely satisfactory visualization of the fetal heart structures was possible in 58% (43%, 56% and 62% at 11, 12 and 13 weeks, respectively). Reference ranges were constructed from the measurements of cardiac ventricles, their outflow tracts, and cardiothoracic circumference ratio in relation to CRL. CONCLUSION: Standard echocardiograhic views of the fetal heart can be obtained at 11 + 0 to 13 + 6 weeks of gestation using the transvaginal approach. New reference ranges were established for fetal cardiac biometry at 11 + 0 to 13 + 6 weeks of gestation.     

Evaluation of fetal sonographic measurements in the first trimester by transvaginal sonography.

To assess the reliability of early biometric measurements in pregnancy, transvaginal sonography was performed in 92 pregnancies in the first trimester in a cross-sectional fashion. Measurements included crown-to-rump length (CRL), biparietal diameter (BPD), head and abdominal circumference (HC and AC), and femur length (FL). Stepwise regression analysis of the gestational age was performed. CRL maintained the highest correlation with gestational age (r = 0.99, p less than 0.001). BPD, HC, AC also correlated well. FL showed a less strong correlation with gestational age (r = 0.76, p less than 0.001). CRL remains the standard for early sonography measurements.     

Fetal biometry: clinical, pathological, and technical considerations

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

Ultrasonographic ear length measurement in normal second- and third-trimester fetuses

OBJECTIVE: We sought to develop a nomogram for fetal ear length measurements from a large population of healthy second- and third-trimester fetuses and to investigate the correlation of fetal ear length with other standard fetal biometry measurements, as follows: biparietal diameter, head circumference, abdominal circumference, femur length, and humerus length. STUDY DESIGN: Ear length measurement was obtained prospectively in 4240 singleton fetuses between 15 and 40 weeks' gestational age. Either complete data for normal karyotype on amniocentesis or normal infant examination at birth or both were available in 2583 cases. These constituted the final study population. RESULTS: A nomogram was developed by linearly regressing ear length on gestational age (Ear length [in millimeters] = 1.076 x Gestational age [in weeks] - 7. 308). There was a high correlation between ear length and gestational age (r = 0.96; P =.0001). CONCLUSION: The results of this study provide normative data on growth of fetal ear length from 15 to 40 weeks' gestation. Good correlation was also observed between ear length and other fetal biometric measurements (biparietal diameter, head circumference, abdominal circumference, femur length, and humerus length).     

Agreement between two 3D ultrasound techniques for the assessment of the subpubic arch angle

Objectives: To assess the reliability of a new three-dimensional (3D) ultrasound technique for the measurement of the subpubic arch angle (SPA) and the agreement between two contrast-enhancing 3D ultrasound techniques.

Methods: We acquired two static 3D transperineal volumes from 72 nulliparous women using two ultrasound machines equipped with two different 3D contrast enhancement and linear reconstruction softwares: 1. Oblique View Extended Imaging with HD-Volume Imaging (OVIX-HDVI?), Samsung; 2. Omniview with Volume Contrast Imaging (Omniview-VCI?), GE Healthcare. An operator measured SPA once by OVIX-HDVI, and twice by Omniview-VCI, while another operator measured SPA once by Omniview-VCI. We evaluated intra- and inter-observer reproducibility of Omniview-VCI and intermethod agreement. Reproducibility and intermethod agreement were studied by means of intraclass correlation coefficient (ICC) and Bland–Altman method.

Results: Omniview-VCI SPA measurements showed excellent intraobserver and interobserver reproducibility (ICC 0.970; 95% C.I. 0.952 to 0.981, 0.932; 95% C.I. 0.893 to 0.957, respectively). Furthermore, Omniview VCI SPA measurements demonstrated excellent agreement with those performed by OVIX-HDVI technique (ICC 0.943; 95 C.I. 0.911 to 0.964). No systematic difference was found in any of the reliability studies.

Conclusions: OmniView-VCI is a reliable method for SPA assessment. Both OmniView-VCI and OVIX-HDVI can be used interchangeably for SPA measurement.     

Ultrasound biometry of Arabian fetuses.

OBJECTIVE: To establish fetal ultrasound biometry charts for Arabian fetuses between 14 and 40 weeks of gestation. METHOD: Cross-sectional fetal ultrasound data of normal singleton pregnancies, which had been performed over a period of 7 years, were retrieved. Only pregnant Arab women with certain last menstrual period dates and/or early ultrasound examinations were included. Each fetus contributed to only one set of data. Normal ranges for biparietal diameter (BPD), head circumference (HC), abdominal circumference (AC), and femur length (FL) were established. The mean and 5th and 95th percentiles at 18th, 28th, and 36 weeks of gestation were compared with similar ranges of published data from pregnancies of American and Anglo-Saxon population. RESULTS: Fetal ultrasound biometry has been established for our local population. Comparing our data with Western population emphasizes the presence of significant variation in fetal morphometric measurements, particularly in the later weeks of gestation and at the extremes of the range of fetal size. CONCLUSION: The clinical significance of this variation differs according to the primary objective of ultrasound fetal measurements. For estimation of fetal age, usually by head and femur measurements in early gestation, ethnic variation seems to have limited significance. Whereas for estimation of fetal growth and/or weight in the third trimester, based on abdominal circumference, the use of given points, e.g., 10th or 5th percentile derived from other population charts, has the potential of either over- or underdiagnosis of IUGR fetuses. The adoption of locally developed charts is recommended.     

Assessment of gestational age of the Asian fetus by the sonar measurement of crown-rump length and biparietal diameter

Summary. Two populations of pregnant Asian and European women were scanned using linear array real-time ultrasound machines. Measurements were made of fetal crown-rump length (CRL) up to 14 weeks gestational age and of biparietal diameter (BPD) up to 20 weeks gestational age. Polynomial growth curves relating CRL and BPD measurements to their gestational ages were fitted to the data by the method of unweighted least squares. There were no significant differences between the Asian and European parameters for the CRL and BPD curves. European nomograms may be used to establish Asian fetal gestational age up to 20 weeks.     

Fetal ultrasound biometry: 2. Abdomen and femur length reference values

Objective To create reliable reference ranges and calculate Z scores for fetal abdomen and femur ultrasound biometry using a large sample size which is evenly distributed from 12 to 42 weeks of pregnancy.
Design A prospective, cross-sectional study.
Setting Obstetric clinics (outpatient and delivery units) at the University Hospital of Zurich.
Sample The study data were obtained from 6557 pregnant women.
Methods Only the first ultrasound examination between 12 and 42 weeks of each fetus with certainly established gestational age was used for analysis. No exclusions were made on the grounds of small-for-date birthweight, prematurity or other events several weeks after the examination. Separate regression models were fitted to estimate the mean and standard deviation at each gestational age for each parameter.
Results A total of 5807 mean abdominal diameters and abdominal circumferences were derived from fetal transverse and anterio-posterior fetal abdominal diameter measurements. Fetal femur length was measured in 5860 instances. The charts, tables and regression formulae of the biometrical measurements are presented. A comparison of our charts with others showed no significant difference. Only Merz's ¹ centiles for abdominal biometry were lower and for femur length higher than ours. An application to calculate 2 scores was developed using Excel (Microsoft Corporation, USA); the macros are presented in detail in the Figure 6 footnote .
Conclusions We have presented centile charts, tables and formulae for fetal abdominal diameter and circumference and femur length derived from a large and minimally selected sample size in a carefully designed cross-sectional study. Complete tables and regression formulae to calculate reference ranges and Z scores are presented to use in computer-aided evaluation of fetal ultrasound biometry.     

Fetal ultrasound biometry: 2. Abdomen and femur length reference values.

OBJECTIVE: To create reliable reference ranges and calculate Z scores for fetal abdomen and femur ultrasound biometry using a large sample size which is evenly distributed from 12 to 42 weeks of pregnancy. DESIGN: A prospective, cross-sectional study. SETTING: Obstetric clinics (outpatient and delivery units) at the University Hospital of Zurich. SAMPLE: The study data were obtained from 6557 pregnant women. METHODS: Only the first ultrasound examination between 12 and 42 weeks of each fetus with certainly established gestational age was used for analysis. No exclusions were made on the grounds of small-for-date birthweight, prematurity or other events several weeks after the examination. Separate regression models were fitted to estimate the mean and standard deviation at each gestational age for each parameter. RESULTS: A total of 5807 mean abdominal diameters and abdominal circumferences were derived from fetal transverse and anterio-posterior fetal abdominal diameter measurements. Fetal femur length was measured in 5860 instances. The charts, tables and regression formulae of the biometrical measurements are presented. A comparison of our charts with others showed no significant difference. Only Merz's centiles for abdominal biometry were lower and for femur length higher than ours. An application to calculate Z scores was developed using Excel (Microsoft Corporation, USA); the macros are presented in detail in the Figure 6 footnote. CONCLUSIONS: We have presented centile charts, tables and formulae for fetal abdominal diameter and circumference and femur length derived from a large and minimally selected sample size in a carefully designed cross-sectional study. Complete tables and regression formulae to calculate reference ranges and Z scores are presented to use in computer-aided evaluation of fetal ultrasound biometry.     

Intra- and interobserver agreement on cervical volume and flow indices during pregnancy using transvaginal 3-dimensional ultrasonography and Doppler angiography

OBJECTIVES: To assess intra- and interobserver agreement in cervical volume and flow indices measurements. METHOD: We prospectively examined 126 patients by two seperate observers using transvaginal 3D gray-scale and power Doppler ultrasound. The two acquired volume datasets were analyzed using the VOCAL imaging program for assessing cervical volume, vascularization index (VI), flow index (FI), and vascularization flow index (VFI). Reproducibility of volume and vascularity measurement was assessed by calculating intraclass (intra-CC) and interclass (inter-CC) correlation coefficients (ICCs). RESULTS: Both intraobserver and interobserver cervical volume measurements were in perfect agreement with intra-CC values of 0.95, 0.96 for both examiners and with an inter-CC value of 0.95. Intraobserver agreement for VI, FI and VFI measurements were as good as the interobserver agreement for VI, and VFI measurements were adequate but less for FI measurements (inter-CC 0.67). Overall, volumetric data were more reliably acquirable than power Doppler measurements. CONCLUSIONS: 3D ultrasound gray-scale and power Doppler measurement of cervical volume and vascularization have acceptable intra- and interobserver variations and thus may be used in clinical research of cervical physiology and pathophysiology during pregnancy.     

First-trimester reference centiles of fetal biometry in Indian population

Aim and objective: To create crown-rump length (CRL)-based biometric chart for fetus in the first trimester among the Indian population.

Material and methods: Cross-sectional data were obtained from 400 singleton pregnancies between 11 and 14 weeks gestation with a normal outcome. Linear regression models were constructed; the mean and SD were derived as a function of CRL.

Results: There was a positive correlation of CRL with nuchal translucency (NT) (y?=?0.0102x?+?0.6307 R^2?=^?0.1177), biparietal diameter (BPD) (BPD?=?0.032*CRL +0.185 R^2?=^?0.765), occipito-frontal diameter (OFD), lateral ventricular diameter (LV), abdominal circumference (AC) (AC?=?0.944*CRL +9.684 R^2?=^?0.668), femur length (FL) (FL?=?0.222*CRL ?4.734 R^2?=^?0.661), fetal weight (FW) (FW?=?1.328*CRL ?10.41 R^2?=^?0.662). The regression models and centile charts of NT, BPD, OFD, LV, AC, and FW were constructed. Taking FW as the independent variable, a linear equation of BPD, AC, and FL to calculate weight was constructed.

Conclusions: The first-trimester centile charts of fetal parameters can be used as a reference for Indian population in the determination of gestational age or other adverse outcomes.     

First-trimester screening for fetal triploidy at 11 to 14 weeks: a role for fetal biometry

OBJECTIVE: Intrauterine growth restriction in triploidy has been reported as early as in the first trimester. This study was undertaken to evaluate the ability of first-trimester crown rump length (CRL)-based charts to detect triploid fetuses. MATERIAL AND METHODS: Analysis of fetal biometry in cases of triploidy diagnosed in the first trimester over the last three years. Biometry for abdominal circumference (AC), head circumference (HC) and biparietal diameter (BPD) was analyzed in relation to both gestational age (GA)-based charts and to CRL-based charts. RESULTS: Five cases of fetal triploidy were diagnosed at 11 to 14 weeks. Screening based on nuchal translucency (NT) and maternal age showed a risk > 1/300 in only one of the 5 cases of triploid fetus. In all of these five cases, CRL-based biometry was grossly abnormal, although it was abnormal in only two of these five cases in relation to GA-based charts. CONCLUSION: First-trimester CRL-based biometry charts seem to reflect early asymmetrical growth delay in triploidy more accurately than GA-based charts. CRL-based biometry is likely to improve the early detection of triploid pregnancies without leading to dating error.