Scientific basis for standardization of fetal head measurements by ultrasound: a reproducibility study

Biparietal diameter for first-trimester pregnancy dating: multicenter cohort study

OBJECTIVE

To evaluate the accuracy of fetal biparietal diameter (BPD) measurement in comparison with crown-rump length (CRL) measurement for pregnancy dating at 11-13 weeks' gestation.

METHODS

This was a retrospective multicenter cohort study performed in five maternity units in Spain, the UK, Belgium and Bulgaria between January 2011 and December 2019. We included all women who attended a routine ultrasound examination at 11 + 0 to 13 + 6 weeks who had a singleton pregnancy with a viable non-malformed fetus/neonate and ultrasound-derived measurements for both CRL and BPD, along with a comprehensive record of pregnancy outcomes. We developed a formula for pregnancy dating based on BPD using data from pregnancies conceived via in-vitro fertilization (IVF) by applying a simple linear regression. We validated this formula both internally and externally and compared it with the most commonly used formulae (Robinson's CRL-based and Kustermann's BPD-based formulae) through utilization of the Euclidean distance, relative absolute error and mean squared error. We also examined the rate of induction of labor for post-term pregnancy based on dating using each of the formulae.

RESULTS

A total of 49 492 women were included in the study, comprising 47 223 (95.4%) who conceived spontaneously and 2269 (4.6%) who conceived via IVF. In the internal validation performed using data from IVF pregnancies, our newly developed formula showed no significant difference when compared with the true gestational age calculated using conception date, with a mean difference of 0.0006 (95% CI, -0.09 to 0.09) days. In contrast, the mean difference of Kustermann's BPD-based formula was -0.31 (95% CI, -0.46 to -0.17) days and the mean difference of Robinson's CRL-based formula was -1.78 (95% CI, -1.88 to -1.68) days. In the external validation using data from spontaneously conceived pregnancies, with dating using Robinson's formula as the reference for 'true' gestational age, both our formula and Kustermann's formula resulted in underestimation of gestational age, with significant mean differences of -1.25 (95% CI, -1.28 to -1.22) days and -0.96 (95% CI, -0.98 to -0.93) days, respectively. The largest differences compared with Robinson's formula-based dating results were observed between 11 + 0 and 12 + 0 weeks. Dating the pregnancy using Robinson's formula led to 8.1% of pregnancies identified as requiring induction after 41 + 3 weeks, compared with 6.8% (P < 0.001) and 7.0% (P < 0.001) when applying our formula and Kustermann's formula, respectively.

CONCLUSION

Pregnancy dating based on ultrasound measurement of fetal BPD between 11 + 0 and 13 + 6 weeks' gestation is a reliable alternative to dating based on fetal CRL. © 2025 International Society of Ultrasound in Obstetrics and Gynecology.

Modality-level obstacles and initiatives to improve representation in fetal, infant, and toddler neuroimaging research samples

Fetal, infant, and toddler (FIT) neuroimaging researchers study early brain development to gain insights into neurodevelopmental processes and identify early markers of neurobiological vulnerabilities to target for intervention. However, the field has historically excluded people from global majority countries and from marginalized communities in FIT neuroimaging research. Inclusive and representative samples are essential for generalizing findings across neuroimaging modalities, such as magnetic resonance imaging, magnetoencephalography, electroencephalography, functional near-infrared spectroscopy, and cranial ultrasonography. These FIT neuroimaging techniques pose unique and overlapping challenges to equitable representation in research through sampling bias, technical constraints, limited accessibility, and insufficient resources. The present article adds to the conversation around the need to improve inclusivity by highlighting modality-specific historical and current obstacles and ongoing initiatives. We conclude by discussing tangible solutions that transcend individual modalities, ultimately providing recommendations to promote equitable FIT neuroscience.

Reproducibility of fetal ultrasound doppler parameters used for growth assessment

OBJECTIVES

To produce standards of references for quality control and assess the reproducibility of fetal ultrasound Doppler measurements commonly used for blood flow assessment in fetal growth.

METHODS

Women with singleton normal pregnancies were prospectively recruited at University College London Hospital, UK, between 24 and 41 weeks. Umbilical artery (UA), middle cerebral artery (MCA), and their pulsatility indices (PI), resistance indices (RI) and ratios such as cerebro-placental (CPR) and umbilical cerebral ratio (UCR) were obtained twice by two sonographers in training or after completion of training, blind to each other's measurements. Bland-Altman plots were generated, the mean differences and 95% limits of agreement (LOA) were calculated to assess intra- and interobserver reproducibility. Values were expressed as absolute values or as z-score.

RESULTS

One hundred ten women were recruited. Overall reproducibility was variable for absolute values and highly variable for z-scores, independently from vessel sampled, index or ratio used, intra- or interobserver reproducibility. The widest absolute values of 95% LOA were 0.3 for UA PI, 0.7 for MCA PI, 0.9 for CPR and 0.3 for UCR, respectively. Regarding z-score, the widest 95% LOA were 1.9 for UA PI, 2.1 for CPR and 1 for UCR. Reproducibility was slightly better for intra- compared with interobserver variability. There was significant difference in z-score reproducibility between MCA peak systolic velocity and CPR vs UCR.

CONCLUSIONS

Reference standards of reproducibility of fetal Doppler parameters are produced for standardization and quality-control purposes. Overall, the reproducibility for fetal Doppler parameters was variable independently from vessel sampled, Doppler index (PI or RI) or ratio used, intra- and interobserver comparison. UCR was the most reproducible parameter which should be recommended, together with UA PI, for clinical use and in research studies on fetal growth.

Transvaginal cervical cerclage: double monofilament modified Wurm vs single braided McDonald technique

OBJECTIVE

To compare pregnancy outcome in women at high risk of preterm birth undergoing the modified Wurm (two monofilament sutures) vs those undergoing the McDonald (single braided suture) transvaginal cervical cerclage technique.

METHODS

This was a single-center prospective observational study of all women with a singleton pregnancy attending a prematurity surveillance clinic because of an increased risk of preterm birth, and undergoing history- or ultrasound-indicated transvaginal cervical cerclage. Two cerclage techniques were evaluated and the choice of cerclage was at the physician's discretion. In the modified Wurm technique using monofilament material, two circumferential sutures are placed with two insertions each (four in total). Outcomes were compared vs those of women undergoing the McDonald technique (single braided suture using a diamond-type insertion method with four insertions in total). Primary outcome was the rate of preterm birth at < 32 weeks' gestation, with planned subanalyses according to cervical cerclage indication (history- or ultrasound-indicated), preterm birth rate at any gestational age (< 37, < 34, < 28 and < 24 weeks), and sonographic cervical length (CL) of ≤ 25 mm and ≤ 15 mm. Secondary outcome measures included maternal and neonatal adverse events and outcomes, including the pre- and postsurgical characteristics. In addition, a reproducibility analysis using Bland-Altman plots was performed to evaluate the intra- and interobserver reproducibility in assessment of CL on ultrasound examination before and after cerclage.

RESULTS

In total, 147 patients were included in the final analysis: 55 (37%) received modified Wurm cerclage and 92 (63%) received McDonald cerclage. Other than race, demographic characteristics were comparable between the two groups. Of these, 22 (40%) women in the modified Wurm group had history-indicated cerclage, vs 50 (54%) women in the McDonald group; the remaining cerclages were ultrasound-indicated. In women with a short CL (≤ 25 mm), there was a significantly lower rate of preterm birth at < 32 weeks' gestation after modified Wurm compared with the McDonald technique (3 (9%) vs 14 (29%); adjusted odds ratio (aOR), 0.25 (95% CI, 0.06-0.95); P = 0.042). However, the study was underpowered to provide definitive conclusions. In the overall population, there was no significant difference in preterm birth rate for < 32 weeks' gestation between the two techniques (7 (13%) vs 22 (24%); aOR, 0.51 (95% CI, 0.20-1.33); P = 0.169). There was no difference in overall surgical complications between the two techniques. The pregnancy loss rate and composite neonatal morbidity/mortality rate were comparable between the two groups (2 (4%) vs 7 (8%); odds ratio (OR), 0.47 (95% CI, 0.09-2.33); P = 0.485; and 5 (9%) vs 11 (13%); OR, 0.68; (95% CI, 0.22-2.09); P = 0.593, respectively).

CONCLUSIONS

In high-risk women with a sonographic short CL, placement of a modified Wurm cervical cerclage is associated with a lower rate of preterm birth < 32 weeks compared with McDonald cervical cerclage. Further research in larger cohorts is needed to confirm this finding and to determine if this technique reduces the preterm birth rate after elective cervical cerclage without CL shortening. © 2025 The Author(s). Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology.

Three-Dimensional Volume Ultrasound Assessment of Cesarean Scar Niche and Cervix in Pregnant Women: A Reproducibility Study

OBJECTIVE

To assess the reproducibility of standardized 3-dimensional (3D) ultrasound volume analysis of the dimensions and the position of cesarean birth (CB) scar niche relative to the cervix in pregnant women.

METHODS

This prospective single-center study in women with 1 previous CB ≥8 cm cervical dilatation acquired ultrasound volumes between 11 and 24 weeks' gestation in a mid-sagittal plane. Two experienced operators processed the volumes using virtual organ computer-aided analysis. A CB scar niche was defined as an indentation at the scar site of ≥2 mm in depth. Niche and cervix volumes were calculated using manual contouring. Agreement for categorical variables was expressed using intraclass correlation coefficient (ICC). The Bland-Altman method was used to assess numerical variable reproducibility.

RESULTS

To achieve the desired statistical power, 52 participants were included. The intraobserver agreement on niche classification relative to the internal os was 100%, with an interobserver kappa coefficient of 0.98 (95% confidence interval [CI] 0.97-0.99, P < .05). The intraobserver ICC for niche volume was 0.94 (95% CI 0.90-0.96; P < .001), with a mean difference of -15.32 mm3 (±109.32). The interobserver ICC was 0.78 (95% CI 0.62-0.87; P < .001), with a mean difference of -21.57 mm3 (±202.01). The ICC for niche/cervix volume ratio were 0.94 (95% CI 0.90-0.96; P < .001) and 0.79 (95% CI 0.63-0.87; P < .001) for intra- and interobserver reproducibility, respectively.

CONCLUSIONS

This study demonstrates that 3D CB scar sonographic features are highly reproducible in pregnant women with a history of advanced labor CB. The validated protocol can guide future research on the association with subsequent adverse pregnancy outcomes.

External validation of models to estimate gestational age in the second and third trimester using ultrasound: A prospective multicentre observational study

OBJECTIVES

Accurate assessment of gestational age (GA) is important at both individual and population levels. The most accurate way to estimate GA in women who book late in pregnancy is unknown. The aim of this study was to externally validate the accuracy of equations for GA estimation in late pregnancy and to identify the best equation for estimating GA in women who do not receive an ultrasound scan until the second or third trimester.

DESIGN

This was a prospective, observational cross-sectional study.

SETTING

57 prenatal care centres, France.

PARTICIPANTS

Women with a singleton pregnancy and a previous 11-14-week dating scan that gave the observed GA were recruited over an 8-week period. They underwent a standardised ultrasound examination at one time point during the pregnancy (15-43 weeks), measuring 12 foetal biometric parameters that have previously been identified as useful for GA estimation.

MAIN OUTCOME MEASURES

A total of 189 equations that estimate GA based on foetal biometry were examined and compared with GA estimation based on foetal CRL. Comparisons between the observed GA and the estimated GA were made using R2, calibration slope and intercept. RMSE, mean difference and 95% range of error were also calculated.

RESULTS

A total of 2741 pregnant women were examined. After exclusions, 2339 participants were included. In the 20 best performing equations, the intercept ranged from -0.22 to 0.30, the calibration slope from 0.96 to 1.03 and the RSME from 0.67 to 0.87. Overall, multiparameter models outperformed single-parameter models. Both the 95% range of error and mean difference increased with gestation. Commonly used models based on measurement of the head circumference alone were not amongst the best performing models and were associated with higher 95% error and mean difference.

CONCLUSIONS

We provide strong evidence that GA-specific equations based on multiparameter models should be used to estimate GA in late pregnancy. However, as all methods of GA assessment in late pregnancy are associated with large prediction intervals, efforts to improve access to early antenatal ultrasound must remain a priority.

TRIAL REGISTRATION

The proposal for this study and the corresponding methodological review was registered on PROSPERO international register of systematic reviews (registration number: CRD4201913776).

Which fetal growth charts should be used in France? Position of the French College of Obstetricians and Gynecologists (CNGOF)

OBJECTIVE

To assess which fetal growth charts best describe intrauterine growth in France defined as the ability to classify 10% of fetuses below the 10th percentile (small for gestational age [SGA]) and above the 90th percentile (large for gestational age [LGA]) in the second and third trimesters.

METHODS

We analyzed five studies on fetal ultrasound measurements using three French data sources. Two studies used second and third trimester ultrasound data from a nationwide birth cohort in 2011 (the ELFE study, N = 13 197 and N = 7747); one study used third trimester ultrasound data from on a nationwide cross-sectional study (the 2016 French National Perinatal Survey, N = 9940); and the last two studies were from the "Flash study" 2014 which prospectively collected ultrasound data from routine visits in the second and third trimesters (N = 4858 and N = 3522). For each study, we reported the percentage of measurements below the 10th percentile or above the 90th percentile, using French, Hadlock's, WHO and Intergrowth (IG) charts.

RESULTS

WHO classified 4.7% and 16.3% of fetuses as having an estimated fetal weight (EFW) <10th and >90th percentiles in the second trimester compared to 3.3% and 34.7% with IG. The percentage of fetuses in the third trimester with an EFW <10th and >90th percentiles, ranged from 9.1% to 9.4% and from 8.0% to 11.1%, respectively, for WHO, and from 3.9% to 4.1% and from 17.3% to 21.6%, respectively, for IG. The WHO and IG charts for head circumference were very similar and performed well. Compared to the WHO charts, the French and Hadlock's charts deviated more frequently from the target percentiles values for EFW and biometric measures.

CONCLUSION

It is recommended to use the WHO charts for the assessment of EFW and ultrasound biometric measurements in France (strong recommendation; low quality of evidence).

Etiologically Based Functional Taxonomy of the Preterm Birth Syndrome

Preterm birth (PTB) is a complex syndrome traditionally defined by a single parameter, namely, gestational age at birth (ie, ˂37 weeks). This approach has limitations for clinical usefulness and may explain the lack of progress in identifying cause-specific effective interventions. The authors offer a framework for a functional taxonomy of PTB based on (1) conceptual principles established a priori; (2) known etiologic factors; (3) specific, prospectively identified obstetric and neonatal clinical phenotypes; and (4) postnatal follow-up of growth and development up to 2 years of age. This taxonomy includes maternal, placental, and fetal conditions routinely recorded in data collection systems.

Use of focus point for plane acquisition to improve reproducibility in fetal biometry

OBJECTIVE

To assess the reproducibility of ultrasound measurements of fetal biometry using a 'focus point' to assist the acquisition of the relevant plane.

METHODS

This was a study of 80 women with a singleton non-anomalous pregnancy who attended University College London Hospital, London, UK, between 18 and 37 weeks' gestation. Planes to measure head circumference (HC), abdominal circumference (AC) and femur length (FL) were obtained four times by two different sonographers with different levels of experience, who were blinded to one another; the first set of images was obtained with reference to a standard image, and the second set of images was obtained using the focus point technique. The focus point was defined as a unique fetal anatomical landmark in each plane (cavum septi pellucidi for HC, two-thirds of the umbilical vein for AC and one of the two extremities of the diaphysis for FL). Once identified, the focus point was maintained in view while the sonographer rotated the probe along three axes (x, y, z) to acquire the relevant plane. Sonographers were either in training or had > 3000 scans worth of experience. Intra- and interobserver reproducibility were assessed using Bland-Altman plots, and absolute values and percentages for mean difference and 95% limits of agreement (LoA) were reported.

RESULTS

Overall reproducibility was good, with all 95% LoA < 8%. Reproducibility was improved by use of the focus point compared with the standard technique for both intraobserver comparison (95% LoA, < 4% vs < 6%) and interobserver comparison (95% LoA, < 7% vs < 8%). These findings were independent of sonographer seniority and plane acquired.

CONCLUSIONS

Reproducibility of fetal biometry assessment is improved with use of the focus point for plane acquisition, regardless of sonographer experience. We propose that this method should be implemented in clinical practice and training programs in fetal biometry. © 2023 The Authors. Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology.

Management of late-onset fetal growth restriction: pragmatic approach

OBJECTIVES

There is limited prospective evidence to guide the management of late-onset fetal growth restriction (FGR) and its differentiation from small-for-gestational age. The aim of this study was to assess prospectively a novel protocol in which ultrasound criteria were used to classify women with suspected late FGR into two groups: those at low risk, who were managed expectantly until the anticipated date of delivery, and those at high risk, who were delivered soon after 37 weeks of gestation. We also compared the outcome of this prospective cohort with that of a historical cohort of women presenting similarly with suspected late FGR, in order to evaluate the impact of the new protocol.

METHODS

This was a prospective study of women with a non-anomalous singleton pregnancy at ≥ 32 weeks' gestation attending a tertiary hospital in London, UK, between February 2018 and September 2019, with estimated fetal weight (EFW) ≤ 10th centile, or EFW > 10th centile in addition to a decrease in fetal abdominal circumference of ≥ 50 centiles compared with a previous scan, umbilical artery Doppler pulsatility index > 95th centile or cerebroplacental ratio < 5th centile. Women were classified as low or high risk based on ultrasound and Doppler criteria. Women in the low-risk group were delivered by 41 weeks of gestation, unless they subsequently met high-risk criteria, whereas women in the high-risk group (EFW < 3rd centile, umbilical artery Doppler pulsatility index > 95th centile or EFW between 3rd and 10th centiles (inclusive) with abdominal circumference drop or abnormal Dopplers) were delivered at or soon after 37 weeks. The primary outcome was adverse neonatal outcome and included hypothermia, hypoglycemia, neonatal unit admission, jaundice requiring treatment, suspected infection, feeding difficulties, 1-min Apgar score < 7, hospital readmission and any severe adverse neonatal outcome (perinatal death, resuscitation using inotropes or mechanical ventilation, 5-min Apgar score < 7, metabolic acidosis, sepsis, and cerebral, cardiac or respiratory morbidity). Secondary outcomes were adverse maternal outcome (operative delivery for abnormal fetal heart rate) and severe adverse neonatal outcome. Women managed according to the new protocol were compared with a historical cohort of 323 women delivered prior to the implementation of the new protocol, for whom management was guided by individual clinician expertise.

RESULTS

Over 18 months, 321 women were recruited to the prospective cohort, of whom 156 were classified as low risk and 165 were high risk. Adverse neonatal outcome was significantly less common in the low-risk compared with the high-risk group (45% vs 58%; adjusted odds ratio (aOR), 0.6 (95% CI, 0.4-0.9); P = 0.022). There was no significant difference in the rate of adverse maternal outcome (18% vs 24%; aOR, 0.7 (95% CI, 0.4-1.2); P = 0.142) or severe adverse neonatal outcome (3.8% vs 8.5%; aOR, 0.5 (95% CI, 0.2-1.3); P = 0.153) between the low- and high-risk groups. Compared with women in the historical cohort classified retrospectively as low risk, low-risk women managed under the new protocol had a lower rate of adverse neonatal outcome (45% vs 58%; aOR, 0.6 (95% CI, 0.4-0.9); P = 0.026).

CONCLUSIONS

Appropriate risk stratification to guide management of late FGR was associated with a reduced rate of adverse neonatal outcome in low-risk pregnancies. In clinical practice, a policy of expectantly managing women with a low-risk late-onset FGR pregnancy at term could improve neonatal and long-term development. Randomized controlled trials are needed to assess the effect of an evidence-based conservative management protocol for late FGR on perinatal morbidity and mortality and long-term neurodevelopment. © 2023 The Authors. Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology.

Training in Obstetric Ultrasound Biometry: Results from a Multicenter Reproducibility Study

OBJECTIVES

To assess the intra- and interobserver reproducibility of fetal biometry measurements obtained by trainee (junior) and experienced sonographers (senior) in the contest of two training programs in obstetric ultrasound.

METHODS

This was a prospective study on 192 women recruited ensuring an even distribution throughout gestation (18-41 weeks), at University College London Hospital (UCLH), England (87 cases), and at Maternité Regionale Universitaire de Nancy (MRUN), France (105 cases). The training took place in two training centers with experience in ultrasound training and subspecialist training in fetal medicine. Measurements for head circumference (HC), abdominal circumference (AC), and femur length (FL) were obtained twice by junior and senior sonographers, blind to their own and each other's measurements. Differences between and within sonographers were expressed in millimeters and as a percentage of fetal dimensions. Reproducibility was assessed using Bland-Altman plots.

RESULTS

Reproducibility was overall high with 95% confidence intervals (CI) within <6% for intraobserver and <8% for interobserver reproducibility. Intraobserver reproducibility was lower within junior than within senior sonographers' measurements for HC (95% CI: <4% versus <3%) and FL (95% CI: <6% and < 5%). Intraobserver reproducibility was similar between the two centers/training programs (AC 95% CI: <6%). Cumulative interobserver reproducibility in both centers was similar to the reproducibility within a single site (95% CI: <5%, <8%, and <7% for HC, AC, and FL, respectively).

CONCLUSIONS

Reproducibility of fetal biometry measurement was high in centers with structured training programs regardless of sonographers' experience. Reproducibility was higher in sonographers who completed the training.

Reproducibility of assessment of full-dilatation Cesarean section scar in women undergoing second-trimester screening for preterm birth

OBJECTIVE

To assess the reproducibility of a standardized method of measuring the Cesarean section (CS) scar, CS scar niche and their position relative to the internal os of the uterine cervix by transvaginal ultrasound in pregnant women with a previous full-dilatation CS.

METHODS

This was a prospective, single-center reproducibility study on women with a singleton pregnancy and a previous full-dilatation CS who underwent transvaginal ultrasound assessment of cervical length and CS scar characteristics at 14-24 weeks' gestation. The CS scar was identified as a hypoechogenic linear discontinuity of the myometrium at the anterior wall of the lower uterine segment or cervix. The CS scar niche was identified as an indentation at the site of the scar with a depth of at least 2 mm. The CS scar position was evaluated by measuring the distance to the internal cervical os. CS scar niche parameters, including its length, depth, width, and residual and adjacent myometrial thickness, were assessed in the sagittal and transverse planes. Qualitative reproducibility was assessed by agreement regarding visibility of the CS scar and niche. Quantitative reproducibility of CS scar measurements was assessed using three sets of images: (1) real-time two-dimensional (2D) images (real-time acquisition and caliper placement on 2D images by two operators), (2) offline 2D still images (offline caliper placement by two operators on stored 2D images acquired by one operator) and (3) three-dimensional (3D) volume images (volume manipulation and caliper placement on 2D images extracted by two operators). Agreement on CS scar visibility and the presence of a niche was analyzed using kappa coefficients. Intraobserver and interobserver reproducibility of quantitative measurements was assessed using Bland-Altman plots.

RESULTS

To achieve the desired statistical power, 72 women were recruited. The CS scar was visualized in > 80% of images. Interobserver agreement for scar visualization and presence of a niche in real-time 2D images was excellent (kappa coefficients of 0.84 and 0.85, respectively). Overall, reproducibility was higher for real-time 2D and offline 2D still images than for 3D volume images. The 95% limits of agreement (LOA) for intraobserver reproducibility were between ± 1.1 and ± 3.6 mm for all sets of images; the 95% LOA for interobserver reproducibility were between ± 2.0 and ± 6.3 mm. Measurement of the distance from the CS scar to the internal cervical os was the most reproducible 2D measurement (intraobserver and interobserver 95% LOA within ± 1.6 and ± 2.7 mm, respectively). Overall, niche measurements were the least reproducible measurements (intraobserver 95% LOA between ± 1.6 and ± 3.6 mm; interobserver 95% LOA between ± 3.1 and ± 6.3 mm). There was no consistent difference between measurements obtained by reacquisition of 2D images (planes obtained twice and caliper placed), caliper placement on 2D stored images or volume manipulation (planes obtained twice and caliper placed).

CONCLUSIONS

The CS scar position and scar niche in pregnant women with a previous full-dilatation CS can be assessed in the second trimester of a subsequent pregnancy using either 2D or 3D volume ultrasound imaging with a high level of reproducibility. Overall, the most reproducible CS scar parameter is the distance from the CS scar to the internal cervical os. The method proposed in this study should enable clinicians to assess the CS scar reliably and may help predict pregnancy outcome. © 2022 The Authors. Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology.

Ultrasound Diagnosis of the Small and Large Fetus

Antenatal imaging is crucial in the management of high-risk pregnancies. Accurate dating relies on acquisition of reliable and reproducible ultrasound images and measurements. Quality image acquisition is necessary for assessing fetal growth and performing Doppler measurements to help diagnose pregnancy complications, stratify risk, and guide management. Further research is needed to ascertain whether current methods for estimating fetal weight can be improved with 3-dimensional ultrasound or magnetic resonance imaging; optimize dating with late initiation of prenatal care; minimize under-diagnosis of fetal growth restriction; and identify the best strategies to make ultrasound more available in low-income and middle-income countries.

A Systematic Review of Methodology Used in Studies Aimed at Creating Charts of Fetal Brain Structures

Ultrasound-based assessment of the fetal nervous system is routinely recommended at the time of the mid-trimester anatomy scan or at different gestations based on clinical indications. This review evaluates the methodological quality of studies aimed at creating charts for fetal brain structures obtained by ultrasound, as poor methodology could explain substantial variability in percentiles reported. Electronic databases (MEDLINE, EMBASE, Cochrane Library, and Web of Science) were searched from January 1970 to January 2021 to select studies on singleton fetuses, where the main aim was to construct charts on one or more clinically relevant structures obtained in the axial plane: parieto-occipital fissure, Sylvian fissure, anterior ventricle, posterior ventricle, transcerebellar diameter, and cisterna magna. Studies were scored against 29 predefined methodological quality criteria to identify the risk of bias. In total, 42 studies met the inclusion criteria, providing data for 45,626 fetuses. Substantial heterogeneity was identified in the methodological quality of included studies, and this may explain the high variability in centiles reported. In 80% of the studies, a high risk of bias was found in more than 50% of the domains scored. In conclusion, charts to be used in clinical practice and research should have an optimal study design in order to minimise the risk of bias and to allow comparison between different studies. We propose to use charts from studies with the highest methodological quality.

Quality control of fetal biometric evaluation and Doppler ultrasound

In recent years quality control in obstetric ultrasound has become recommended and an essential component of obstetric scanning. This is to minimize the inaccuracy and variability related to fetal measurements, to provide an effective quality assurance system to sonographers to certify their practice and decrease the impact of medical litigations. For a quality control system in obstetric ultrasound to be useful clinically, multiple strategies need to be employed: certified training, practical standardization exercise, image storing, qualitative and quantitative quality control. Qualitative quality control consists of the evaluation of images obtained for fetal biometry and Doppler scans using an objective score against predefined criteria. Quantitative quality control consists of analyzing quantitatively the performance of a sonographer and the impact on measurements values. Quantitative analysis could be performed either using estimates of intraobserver or interobserver reproducibility of plane acquisition and caliper placements.

Support vector regression algorithm modeling to predict the parturition date of small - to medium-sized dogs using maternal weight and fetal biparietal diameter

Background and Aim:

Fetal biparietal diameter (BPD) is a feasible parameter to predict canine parturition date due to its inverted correlation with days before parturition (DBP). Although such a relationship is generally described using a simple linear regression (SLR) model, the imprecision of this model in predicting the parturition date in small- to medium-sized dogs is a common problem among veterinarian practitioners. Support vector regression (SVR) is a useful machine learning model for prediction. This study aimed to compare the accuracy of SVR with that of SLR in predicting DBP.

Materials and Methods:

After measuring 101 BPDs in 35 small- to medium-sized pregnant bitches, we fitted the data to the routine SLR model and the SVR model using three different kernel functions, radial basis function SVR, linear SVR, and polynomial SVR. The predicted DBP acquired from each model was further utilized for calculating the coefficient of determination (R2), mean absolute error, and mean squared error scores for determining the prediction accuracy.

Results:

All SVR models were more accurate than the SLR model at predicting DBP. The linear and polynomial SVRs were identified as the two most accurate models (p<0.01).

Conclusion:

With available machine learning software, linear and polynomial SVRs can be applied to predicting DBP in small- to medium-sized pregnant bitches.

The impact of optimal dating on the assessment of fetal growth

BACKGROUND

The impact of using the Intergrowth (IG) dating formulae in comparison to the commonly used Robinson dating on the evaluation of biometrics and estimated fetal weight (EFW) has not been evaluated.

METHODS

Nationwide cross-sectional study of routine fetal ultrasound biometry in low-risk pregnant women whose gestational age (GA) had been previously assessed by a first trimester CRL measurement. We compared the CRL-based GA according to the Robinson formula and the IG formula. We evaluated the fetal biometric measurements as well as the EFW taken later in pregnancy depending on the dating formula used. Mean and standard deviation of the Z scores as well as the number and percentage of cases classified as <3rd, < 10th, >90th and > 97th percentile were compared.

RESULTS

Three thousand five hundred twenty-two low-risk women with scans carried out after 18 weeks were included. There were differences of zero, one and 2 days in 642 (18.2%), 2700 (76.7%) and 180 (5%) when GA was estimated based on the Robinson or the IG formula, respectively. The biometry Z scores assessed later in pregnancy were all statistically significantly lower when the Intergrowth-based dating formula was used (p < 10- 4). Likewise, the number and percentage of foetuses classified as <3rd, < 10th, >90th and > 97th percentile demonstrated significant differences. As an example, the proportion of SGA foetuses varied from 3.46 to 4.57% (p = 0.02) and that of LGA foetuses from 17.86 to 13.4% (p < 10- 4).

CONCLUSION

The dating formula used has a quite significant impact on the subsequent evaluation of biometry and EFW. We suggest that the combined and homogeneous use of a recent dating standard, together with prescriptive growth standards established on the same low-risk pregnancies, allows an optimal assessment of fetal growth.

International standards for fetal brain structures based on serial ultrasound measurements from Fetal Growth Longitudinal Study of INTERGROWTH-21st Project

OBJECTIVE

To create prescriptive growth standards for five fetal brain structures, measured using ultrasound, in healthy, well-nourished women at low risk of impaired fetal growth and poor perinatal outcome, taking part in the Fetal Growth Longitudinal Study (FGLS) of the INTERGROWTH-21^st Project.

METHODS

This was a complementary analysis of a large, population-based, multicenter, longitudinal study. The sample analyzed was selected randomly from the overall FGLS population, ensuring an equal distribution among the eight diverse participating sites and of three-dimensional (3D) ultrasound volumes across pregnancy (range: 15-36 weeks' gestation). We measured, in planes reconstructed from 3D ultrasound volumes of the fetal head at different timepoints in pregnancy, the size of the parieto-occipital fissure (POF), Sylvian fissure (SF), anterior horn of the lateral ventricle, atrium of the posterior horn of the lateral ventricle (PV) and cisterna magna (CM). Fractional polynomials were used to construct the standards. Growth and development of the infants were assessed at 1 and 2 years of age to confirm their adequacy for constructing international standards.

RESULTS

From the entire FGLS cohort of 4321 women, 451 (10.4%) were selected at random. After exclusions, 3D ultrasound volumes from 442 fetuses born without a congenital malformation were used to create the charts. The fetal brain structures of interest were identified in 90% of cases. All structures, except the PV, showed increasing size with gestational age, and the size of the POF, SF, PV and CM showed increasing variability. The 3^rd , 5^th , 50^th , 95^th and 97^th smoothed centiles are presented. The 5^th centiles for the POF and SF were 3.1 mm and 4.7 mm at 22 weeks' gestation and 4.6 mm and 9.9 mm at 32 weeks, respectively. The 95^th centiles for the PV and CM were 8.5 mm and 7.5 mm at 22 weeks and 8.6 mm and 9.5 mm at 32 weeks, respectively.

CONCLUSIONS

We have produced prescriptive size standards for fetal brain structures based on prospectively enrolled pregnancies at low risk of abnormal outcome. We recommend these as international standards for the assessment of measurements obtained using ultrasound from fetal brain structures. © 2020 Authors. Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology.

Prenatal diagnosis of foetal hydrocephalus and suspected X-linked recessive inheritance of cleft lip in a Chihuahua

A 3.5-year-old, 2.9 kg, multiparous Chihuahua presented with abdominal distension; pregnancy was diagnosed. On Day 7 before parturition, prenatal sonograms showed anechoic bilateral dilated cerebral lateral ventricles, suggesting fluid-filled regions (ventriculomegaly) in one foetus. A Caesarean section was performed and the male newborn had an abnormally enlarged dome-shaped head and a cleft lip, and died 6 days after birth. According to the family pedigree, the X-linked recessive inheritance of an orofacial cleft from the unaffected mother was suggested. This report clearly demonstrates that canine foetal ventriculomegaly (hydrocephalus) can be diagnosed in utero. For dog breeds predisposed to congenital ventriculomegaly, early detection is important for the prediction of perinatal survival and adequate supportive care can be applied at delivery.

Quality-improvement program for ultrasound-based fetal anatomy screening using large-scale clinical audit

OBJECTIVE

A large-scale audit and peer review of ultrasound images may improve sonographer performance, but is rarely performed consistently as it is time-consuming and expensive. The aim of this study was to perform a large-scale audit of routine fetal anatomy scans to assess if a full clinical audit cycle can improve clinical image-acquisition standards.

METHODS

A large-scale, clinical, retrospective audit was conducted of ultrasound images obtained during all routine anomaly scans performed from 18 + 0 to 22 + 6 weeks' gestation at a UK hospital during 2013 (Cycle 1), to build a baseline understanding of the performance of sonographers. Targeted actions were undertaken in response to the findings with the aim of improving departmental performance. A second full-year audit was then performed of fetal anatomy ultrasound images obtained during the following year (Cycle 2). An independent pool of experienced sonographers used an online tool to assess all scans in terms of two parameters: scan completeness (i.e. were all images archived?) and image quality using objective scoring (i.e. were images of high quality?). Both were assessed in each audit at the departmental level and at the individual sonographer level. A random sample of 10% of scans was used to assess interobserver reproducibility.

RESULTS

In Cycle 1 of the audit, 103 501 ultrasound images from 6257 anomaly examinations performed by 22 sonographers were assessed; in Cycle 2, 153 557 images from 6406 scans performed by 25 sonographers were evaluated. The analysis was performed including the images obtained by the 20 sonographers who participated in both cycles. Departmental median scan completeness improved from 72% in the first year to 78% at the second assessment (P < 0.001); median image-quality score for all fetal views improved from 0.83 to 0.86 (P < 0.001). The improvement was greatest for those sonographers who performed poorest in the first audit; with regards to scan completeness, the poorest performing 15% of sonographers in Cycle 1 improved by more than 30 percentage points, and with regards to image quality, the poorest performing 11% in Cycle 1 showed a more than 10% improvement. Interobserver repeatability of scan completeness and image-quality scores across different fetal views were similar to those in the published literature.

CONCLUSIONS

A clinical audit and a set of targeted actions helped improve sonographer scan-acquisition completeness and scan quality. Such adherence to recommended clinical acquisition standards may increase the likelihood of correct measurement and thereby fetal growth assessment, and should allow better detection of abnormalities. As such a large-scale audit is time consuming, further advantages would be achieved if this process could be automated. © 2018 The Authors. Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of the International Society of Ultrasound in Obstetrics and Gynecology.

ISUOG Practice Guidelines: ultrasound assessment of fetal biometry and growth

INTRODUCTION These Guidelines aim to describe appropriate assessment of fetal biometry and diagnosis of fetal growth disorders. These disorders consist mainly of fetal growth restriction (FGR), also referred to as intrauterine growth restriction (IUGR) and often associated with small‐for‐gestational age (SGA), and large‐for‐gestational age (LGA), which may lead to fetal macrosomia; both have been associated with a variety of adverse maternal and perinatal outcomes. Screening for, and adequate management of, fetal growth abnormalities are essential components of antenatal care, and fetal ultrasound plays a key role in assessment of these conditions. The fetal biometric parameters measured most commonly are biparietal diameter (BPD), head circumference (HC), abdominal circumference (AC) and femur diaphysis length (FL). These biometric measurements can be used to estimate fetal weight (EFW) using various different formulae1. It is important to differentiate between the concept of fetal size at a given timepoint and fetal growth, the latter being a dynamic process, the assessment of which requires at least two ultrasound scans separated in time. Maternal history and symptoms, amniotic fluid assessment and Doppler velocimetry can provide additional information that may be used to identify fetuses at risk of adverse pregnancy outcome. Accurate estimation of gestational age is a prerequisite for determining whether fetal size is appropriate‐for‐gestational age (AGA). Except for pregnancies arising from assisted reproductive technology, the date of conception cannot be determined precisely. Clinically, most pregnancies are dated by the last menstrual period, though this may sometimes be uncertain or unreliable. Therefore, dating pregnancies by early ultrasound examination at 8–14 weeks, based on measurement of the fetal crown–rump length (CRL), appears to be the most reliable method to establish gestational age. Once the CRL exceeds 84 mm, HC should be used for pregnancy dating2–4. HC, with or without FL, can be used for estimation of gestational age from the mid‐trimester if a first‐trimester scan is not available and the menstrual history is unreliable. When the expected delivery date has been established by an accurate early scan, subsequent scans should not be used to recalculate the gestational age1. Serial scans can be used to determine if interval growth has been normal. In these Guidelines, we assume that the gestational age is known and has been determined as described above, the pregnancy is singleton and the fetal anatomy is normal. Details of the grades of recommendation used in these Guidelines are given in Appendix 1. Reporting of levels of evidence is not applicable to these Guidelines.

Automated Fetal Head Detection and Circumference Estimation from Free-Hand Ultrasound Sweeps Using Deep Learning in Resource-Limited Countries

Ultrasound imaging remains out of reach for most pregnant women in developing countries because it requires a trained sonographer to acquire and interpret the images. We address this problem by presenting a system that can automatically estimate the fetal head circumference (HC) from data obtained with use of the obstetric sweep protocol (OSP). The OSP consists of multiple pre-defined sweeps with the ultrasound transducer over the abdomen of the pregnant woman. The OSP can be taught within a day to any health care worker without prior knowledge of ultrasound. An experienced sonographer acquired both the standard plane-to obtain the reference HC-and the OSP from 183 pregnant women in St. Luke's Hospital, Wolisso, Ethiopia. The OSP data, which will most likely not contain the standard plane, was used to automatically estimate HC using two fully convolutional neural networks. First, a VGG-Net-inspired network was trained to automatically detect the frames that contained the fetal head. Second, a U-net-inspired network was trained to automatically measure the HC for all frames in which the first network detected a fetal head. The HC was estimated from these frame measurements, and the curve of Hadlock was used to determine gestational age (GA). The results indicated that most automatically estimated GAs fell within the P2.5-P97.5 interval of the Hadlock curve compared with the GAs obtained from the reference HC, so it is possible to automatically estimate GA from OSP data. Our method therefore has potential application for providing maternal care in resource-constrained countries.

Image-scoring system for umbilical and uterine artery pulsed-wave Doppler ultrasound measurement

OBJECTIVES

To develop an objective image-scoring system for pulsed-wave Doppler measurement of maternal uterine and fetal umbilical arteries, and evaluate how this compares with subjective assessment.

METHODS

As an extension to the INTERGROWTH-21^st Project, we developed a scoring system based on six predefined criteria for uterine and umbilical artery pulsed-wave Doppler measurements. Objective evaluation using the scoring system was compared with subjective assessment which consisted of classifying an image as simply acceptable or unacceptable. Based on sample size estimation, a total of 120 umbilical and uterine artery Doppler images were selected randomly from the INTERGROWTH-21^st image database. Two independent reviewers evaluated all images in a blinded fashion, both subjectively and using the six-point scoring system. Percentage agreement and kappa statistic were compared between the two methods.

RESULTS

The overall agreement between reviewers was higher for objective assessment using the scoring system (agreement, 85%; adjusted kappa, 0.70) than for subjective assessment (agreement, 70%; adjusted kappa, 0.47). For the six components of the scoring system, the level of agreement (adjusted kappa) was 0.97 for anatomical site, 0.88 for sweep speed, 0.77 for magnification, 0.68 for velocity scale, 0.68 for image clarity and 0.65 for angle of insonation.

CONCLUSION

In quality assessment of umbilical and uterine artery pulsed-wave Doppler measurements, our proposed objective six-point image-scoring system is associated with greater reproducibility than is subjective assessment. We recommend this as the preferred method for quality control, auditing and teaching. Copyright © 2018 ISUOG. Published by John Wiley & Sons Ltd.

Comparison Study of Low-Cost Ultrasound Devices for Estimation of Gestational Age in Resource-Limited Countries

We investigated how accurately low-cost ultrasound devices can estimate gestational age (GA) using both the standard plane and the obstetric sweep protocol (OSP). The OSP can be taught to health care workers without prior knowledge of ultrasound within one day and thus avoid the need to train dedicated sonographers. Three low-cost ultrasound devices were compared with one high-end ultrasound device. GA was estimated with the head circumference (HC), abdominal circumference (AC) and femur length (FL) using both the standard plane and the OSP. The results revealed that the HC, AC and FL can be used to estimate GA using low-cost ultrasound devices in the standard plane within the inter-observer variability presented in the literature. The OSP can be used to estimate GA by measuring the HC and the AC, but not the FL. This study shows that it is feasible to estimate GA in resource-limited countries with low-cost ultrasound devices using the OSP. This makes it possible to estimate GA and assess fetal growth for pregnant women in rural areas of resource-limited countries.

Quality control of ultrasound for fetal biometry: results from the INTERGROWTH-21st Project

OBJECTIVE

To assess a comprehensive package of ultrasound quality control in the Fetal Growth Longitudinal Study of the INTERGROWTH-21^st Project, a large multicenter study of fetal growth.

METHODS

Quality control (QC) measures were performed for 20 313 ultrasound scan images obtained prospectively from 4321 fetuses at 14-41 weeks' gestation in eight geographical locations. At the time of each ultrasound examination, three fetal biometric variables (head circumference (HC), abdominal circumference (AC) and femur length (FL)) were measured in triplicate on separately generated images. All measurements were taken in a blinded fashion. QC had two elements: (1) qualitative QC: visual assessment by sonographers at each study site of their images based on specific criteria, with 10% of images being re-assessed at the Oxford-based Ultrasound Quality Unit (compared using an adjusted kappa statistic); and (2) quantitative QC: assessment of measurement data by comparing the first, second and third measurements (intraobserver variability), remeasurement of caliper replacement in 10% (interobserver variability), both by Bland-Altman plots and plotting frequency histograms of the SD of triplicate measurements and assessing how many were above or below 2 SD of the expected distribution. The system allowed the sonographers' performances to be monitored regularly.

RESULTS

A high level of agreement between self- and external scoring was demonstrated for all measurements (κ = 0.99 (95% CI, 0.98-0.99) for HC, 0.98 (95% CI, 0.97-0.99) for AC and 0.96 (95% CI, 0.95-0.98) for FL). Intraobserver 95% limits of agreement (LoA) of ultrasound measures for HC, AC and FL were ± 3.3%, ± 5.6% and ± 6.2%, respectively; the corresponding values for interobserver LoA were ± 4.4%, ± 6.0% and ± 5.6%. The SD distribution of triplicate measurements for all biometric variables showed excessive variability for three of 31 sonographers, allowing prompt identification and retraining.

CONCLUSIONS

Qualitative and quantitative QC monitoring was feasible and highly reproducible in a large multicenter research study, which facilitated the production of high-quality ultrasound images. We recommend that the QC system we developed is implemented in future research studies and clinical practice. Copyright © 2017 ISUOG. Published by John Wiley & Sons Ltd.

Biparietal diameter measurements using the outer-to-outer versus outer-to-inner measurement: A question of pedantry?

Objectives

To compare two methods of measuring fetal biparietal diameter (BPD) - outer-to-inner (BPDoi) vs. outer-to-outer (BPDoo) calliper placement - and to compare the differences in EFW calculated using the Hadlock 4 formula and other common EFW formulae.

Methods

A total of 543 fetuses underwent a single ultrasound prospectively performed by 40 sonographers between 14 and 40 weeks of gestation, taking into account the intra- and inter-observer variability. The measurements for each fetus consisted of BPDoi and BPDoo, and EFW is calculated from HC, AC and FL measurements. The difference between BPDoo and BPDoi was estimated, and this difference was compared with gestational age using linear regression. Translational equations that allow interconversion of the two parameters were derived. EFW calculated from four different formulae using various combinations of biometric measurements was compared.

Results

The difference between BPDoi and BPDoo increases with gestational age, although this difference was small. For BPDoo, the regression equation is BPDoo = 0.555934 + 1.027318 × BPDoi. Similarly, for BPDoi, the regression equation is BPDoi = -0.403458 + 0.9714153 × BPDoo. There is a minimal difference in the EFW calculated from the four formulae, except for gestations prior to 27-28 weeks. EFW derived from INTERGROWTH-21st formulae plot is higher than that from Hadlock 3 or Hadlock 4 before 27-28 weeks.

Conclusions

Although the absolute difference between BPDoo and BPDoi increased across gestational age, this difference was small. The method of BPD measurement should follow that as prescribed in the EFW equation used in the local context. Estimation of fetal weight using Hadlock 3, Hadlock 4 and INTERGROWTH-21st is similar, with slight differences at gestations less than 27-28 weeks.

A Deep Learning Solution for Automatic Fetal Neurosonographic Diagnostic Plane Verification Using Clinical Standard Constraints

During routine ultrasound assessment of the fetal brain for biometry estimation and detection of fetal abnormalities, accurate imaging planes must be found by sonologists following a well-defined imaging protocol or clinical standard, which can be difficult for non-experts to do well. This assessment helps provide accurate biometry estimation and the detection of possible brain abnormalities. We describe a machine-learning method to assess automatically that transventricular ultrasound images of the fetal brain have been correctly acquired and meet the required clinical standard. We propose a deep learning solution, which breaks the problem down into three stages: (i) accurate localization of the fetal brain, (ii) detection of regions that contain structures of interest and (iii) learning the acoustic patterns in the regions that enable plane verification. We evaluate the developed methodology on a large real-world clinical data set of 2-D mid-gestation fetal images. We show that the automatic verification method approaches human expert assessment.