Quality of first-trimester measurement of crown-rump length

Introducing and Validating the Cranial-Dorsal-Hip Angle (∠CDH): A Method for Accurate Fetal Position Assessment in the First Trimester and Future AI Applications

Purpose  To introduce the cranial-dorsal-hip angle (∠CDH) as a novel quantitative tool for assessing fetal position in the first trimester and to validate its feasibility for future AI applications. Materials and Methods  2520 first-trimester fetal NT exams with 2582 CRL images (January-August 2022) were analyzed at a tertiary hospital as the pilot group. Additionally, 1418 cases with 1450 fetal CRL images (September-December 2022) were examined for validation. Three expert sonographers defined a standard for fetal positions. ∠CDH measurements, conducted by two ultrasound technicians, were validated for consistency using Bland-Altman plots and the intra-class correlation coefficient (ICC). This method allowed for categorizing fetal positions as hyperflexion, neutral, and hyperextension based on ∠CDH. Comparative accuracy was assessed against Ioannou, Wanyonyi, and Roux methods using the weighted Kappa coefficient (k value). Results  The pilot group comprised 2186 fetal CRL images, and the validation group included 1193 images. Measurement consistency was high (ICCs of 0.993; P<0.001). The established 95% reference range for ∠CDH in the neutral fetal position was 118.3° to 137.8°. The ∠CDH method demonstrated superior accuracy over the Ioannou, Wanyonyi, and Roux methods in both groups, with accuracy rates of 94.5% (k values: 0.874, 95%CI: 0.852-0.896) in the pilot group, and 92.6% (k values: 0.838, 95%CI: 0.806-0.871) in the validation group. Conclusion  The ∠CDH method has been validated as a highly reproducible and accurate technique for first-trimester fetal position assessment. This sets the stage for its potential future integration into intelligent assessment models.

Crown-rump length measurement error: impact on assessment of growth

OBJECTIVE

To examine the impact of first-trimester crown-rump length (CRL) measurement error on the interpretation of estimated fetal weight (EFW) and classification of fetuses as small-, large- or appropriate-for-gestational age on subsequent growth scans.

METHODS

We examined the effects of errors of ± 2, ± 3 and ± 4 mm in the measurement of fetal CRL on percentiles of EFW at 20, 32 and 36 weeks' gestation and classification as small-, large- or appropriate-for-gestational age. Published data on CRL measurement error were used to determine variation present in practice.

RESULTS

A measurement error of -2 mm in first-trimester CRL shifts an EFW on the 10^th percentile at the 20-week scan to around the 20^th percentile, and the effect of a CRL measurement error of + 2 mm would shift an EFW on the 10^th percentile to around the 5^th percentile. At 32 weeks, a first-trimester CRL measurement error would shift an EFW on the 10^th percentile to the 7^th (+ 2 mm) or 14^th (-2 mm) percentile; at 36 weeks, the EFW would shift from the 10^th percentile to the 8^th (+ 2 mm) or 12^th (-2 mm) percentile. Published data suggest that measurement errors of 2 mm or more are common in practice.

CONCLUSION

Because of the widespread and potentially severe consequences of CRL measurement errors as small as 2 mm on clinical assessment, patient management and research results, there is a need to increase awareness of the impact of CRL measurement error and to reduce measurement error variation through standardization and quality control. © 2021 International Society of Ultrasound in Obstetrics and Gynecology.

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.

[Report from the CFEF seminar on fetal biometry (June 2017)]

This article reports the conclusions and recommendations resulting from the seminar organized in Paris on June 15, 2017 by the scientific committee of the French College of Fetal Ultrasound (CFEF). The purpose of this meeting was to audit the practices in screening for SGA and IUGR fetuses in France and to discuss ways to improve ultrasound screening. A review of charts, references, standards and common practices was performed. The potential new biometric tools applicable in France were reviewed and analyzed. Eventually, options and recommendations for improvement are proposed.

Relation between the quality of the ultrasound image acquisition and the precision of the measurement of the crown-rump length in the late first trimester: what are the consequences?

OBJECTIVE

To assess the extent to which the distribution of crown-rump length (CRL) values may be correlated with different criteria for the quality of the CRL images.

STUDY DESIGN

This is a retrospective analysis of a series of 977 CRL images, by two independent observers, for the presence or the absence of 14 quality hallmarks. Inter-observer agreement for the hallmarks was assessed by the proportion of agreement and Cohen's kappa. The association between the quantiles of the CRL distribution and the presence or absence of the 14 quality hallmarks was modeled using quantile regression.

RESULTS

The overall inter-observer agreement across the 14 hallmarks was 91.7%, kappa=0.81, 95% CI [0.80-0.82]. Distribution of CRL measurements varied considerably as a function of image quality: when the fetus was in extension, the mean CRL was +5.7mm (vs. not in extension, p<0.001), when the fetus was in flexion (vs. not), the mean CRL was -4.7mm (p<0.001) and when the image magnification was <65% (vs. >65%), the mean CRL was -4.2mm (p<0.001). There was a global trend to over-estimate the CRL for the higher deciles and to under-estimate the CRL for the lower deciles when the sagittal quality hallmarks were absent. No significant impact on CRL distribution was observed in association with the precise placement of the calipers nor with the horizontal orientation of the fetus.

CONCLUSION

Distribution of CRL measurements was influenced by the quality of CRL images. In particular, inadequate position of the fetus (flexion/extension) and insufficient image magnification were associated with systematic changes in the values of CRL. Our results show that as the quality of CRL images decreases, the associated variations in the distribution of CRL can have an impact on the chromosomal risk assessment and may lead to inappropriate obstetrical decisions.

[How to assess the neutral position of the fetus for the crown-rump length measurement at the nuchal translucency scan]

OBJECTIVES

The objective of this study was to establish a simple and reproducible method for the assessment of the fetal head position when measuring crown-rump length (CRL) at the nuchal translucency scan.

METHODS

Two observers conducted a retrospective analysis of a consecutive series of 570 images of CRL collected by the French College of Fetal Echography (CFEF) national practice assessment program for the first-trimester scan. The images were deemed hyper-flexed if no fluid was visible between the chin and the chest of the fetus. The images were deemed hyper-extended if the angle between the palate and the CRL line was 90° or more. The images were deemed neutral if no hyper-extension nor hyper-flexion was observed.

RESULTS

The proportion of agreement for a non-neutral position of the fetal head was 91.3% (kappa=0.80, 95% CI [0.75 to 0.86]). Images with a non-neutral position corresponded to poor CRL quality images according to the CFEF score (relative risk=4.2, 95% CI [2.9 to 6.1] for one observer and 4.9, 95% CI [3.3 to 7.2] for the other observer). Proportions of agreement for the hyper-flexion and for the hyper-extension were 94.6% (kappa=0.80, 95% CI [0.72 to 0.87]) and 96.8% (kappa=0.81, 95% CI [0.72 to 0.90]), respectively. No additional lines were drawn on the ultrasound images during the evaluation process.

CONCLUSIONS

The proposed method for evaluating the extent to which the fetal head has a non-neutral position at measurement of the CRL appears both simple and reproducible.

[A simple self-assessment tool for the first-trimester ultrasound images]

OBJECTIVES

The objective of this study was to establish a minimum subset of simple criteria for the self-assessment of the quality of first-trimester ultrasound images of nuchal translucency (NT) and crown-rump length (CRL).

METHODS

We designed 162 simplified image-scoring methods (ISM) based on 1, 2, 3 or 4 binary criteria derived from the 8 criteria of the original image scoring method of the French College of Fetal Ultrasound (CFEF). These ISM were assessed on 68,250 consecutive scans of the French national audit conducted by the CFEF on NT and CRL images. The ISM associated with the best precision to identify excellent/reasonable quality scans were selected.

RESULTS

Simplified ISM based on 1, 2, 3 and 4 criteria showed maximum positive predictive values of 95.3% (95.11-95.50) 98.0% (97.87-98.14), 99.3% (99.17-99.35) and 99.7% (99.68-99.79), respectively, to identify excellent/reasonable quality scans. The proportion of excellent/reasonable scans was 2.8 to 16.7% when three criteria among the 8 were insufficient, and 0.17 to 3.95% when four criteria were insufficient.

CONCLUSIONS

The best performing ISM was based on the following four quality criteria: (i) sagittal plane of the NT, (ii) calipers placement for measuring the NT, (iii) image magnification of NT images and (iv) CRL measurement. This score might be the most relevant in clinical practice in the first-trimester screening.