Analysis of quality of nuchal translucency measurements: its role in prenatal diagnosis

Ultrasonographic Fetal Nuchal Translucency Measurements and Cytogenetic Outcomes

Importance

Ultrasonographic measurement of fetal nuchal translucency is used in prenatal screening for trisomies 21 and 18 and other conditions. A cutoff of 3.5 mm or greater is commonly used to offer follow-up investigations, such as prenatal cell-free DNA (cfDNA) screening or cytogenetic testing. Recent studies showed a possible association with chromosomal anomalies for levels less than 3.5 mm, but extant evidence has limitations.

Objective

To evaluate the association between different nuchal translucency measurements and cytogenetic outcomes on a population level.

Design, Setting, and Participants

This population-based retrospective cohort study used data from the Better Outcomes Registry & Network, the perinatal registry for Ontario, Canada. All singleton pregnancies with an estimated date of delivery from September 1, 2016, to March 31, 2021, were included. Data were analyzed from March 17 to August 14, 2023.

Exposures

Nuchal translucency measurements were identified through multiple-marker screening results.

Main Outcomes and Measures

Chromosomal anomalies were identified through all Ontario laboratory-generated prenatal and postnatal cytogenetic tests. Cytogenetic testing results, supplemented with information from cfDNA screening and clinical examination at birth, were used to identify pregnancies without chromosomal anomalies. Multivariable modified Poisson regression with robust variance estimation and adjustment for gestational age was used to compare cytogenetic outcomes for pregnancies with varying nuchal translucency measurement categories and a reference group with nuchal translucency less than 2.0 mm.

Results

Of 414 268 pregnancies included in the study (mean [SD] maternal age at estimated delivery date, 31.5 [4.7] years), 359 807 (86.9%) had a nuchal translucency less than 2.0 mm; the prevalence of chromosomal anomalies in this group was 0.5%. An increased risk of chromosomal anomalies was associated with increasing nuchal translucency measurements, with an adjusted risk ratio (ARR) of 20.33 (95% CI, 17.58-23.52) and adjusted risk difference (ARD) of 9.94% (95% CI, 8.49%-11.39%) for pregnancies with measurements of 3.0 to less than 3.5 mm. The ARR was 4.97 (95% CI, 3.45-7.17) and the ARD was 1.40% (95% CI, 0.77%-2.04%) when restricted to chromosomal anomalies beyond the commonly screened aneuploidies (excluding trisomies 21, 18, and 13 and sex chromosome aneuploidies).

Conclusions and Relevance

In this cohort study of 414 268 singleton pregnancies, those with nuchal translucency measurements less than 2.0 mm were at the lowest risk of chromosomal anomalies. Risk increased with increasing measurements, including measurements less than 3.5 mm and anomalies not routinely screened by many prenatal genetic screening programs.

Assessment of pericallosal artery at 11-14 weeks of gestation: Cohort study and meta-analysis

OBJECTIVES

To report the rate of visualization of the pericallosal artery (PCA) in the first trimester of pregnancy (11-14 weeks).

METHODS

Prospective observational study of consecutive fetuses undergoing first trimester risk assessment for chromosomal anomalies. The presence of PCA was assessed in a midsagittal view of fetal brain using high-definition power Color Doppler. A normal course of the PCA was defined as the visualization of an artery emerging from the anterior cerebral artery running parallel the corpus callosum (CC). The reference standard was the visualization of CC and PCA between the 20 and 22 weeks of gestation. We also performed a systematic review and meta-analysis of the published literature. Multivariate logistic regression and random-effect meta-analyses of proportion were used to analyze the data.

RESULTS

Cohort study: Five-hundred women were included. PCA was identified trans-abdominally or transvaginally at 11-14 weeks of gestation in 98.8% (95% CI 97.4-99.6: 494/500); of the four cases of PCA not identified one had a diagnosis of complete agenesis of the corpus callosum during the anomaly scan which was confirmed at birth. Systematic review of the published literature: Six studies (1093 fetuses, including the present series) were included. The PCA was detected at the 11-14 weeks scan and confirmed to co-exist with a normal CC at time of the anomaly scan in 96.9% (95% CI 93.8-99.0); 20.6% (95% CI 5.7-41.7) of fetuses with no clear identification of the PCA at the 11-14 weeks scan had a normal appearance of the CC at the time of anomaly scan.

CONCLUSION

Prenatal ultrasonography has a high diagnostic accuracy in detecting PCA in the first trimester. Visualization of the PCA at the time of 11-14 scan is highly specific for the presence of a normal CC later in pregnancy.

Real-time quality control of nuchal translucency measurements using the exponentially weighted moving average chart

OBJECTIVE

The establishment of ongoing audits for first-trimester nuchal translucency (NT) measurements is of paramount importance. The exponentially weighted moving average (EWMA) chart has been published as an efficient tool for NT quality control with the advantages of being suitable for real-time long-term monitoring. This study aimed to assess the efficacy of real-time NT quality control using EWMA charts.

MATERIALS AND METHODS

This was an ongoing prospective study conducted from January 2011 to December 2017 at the Centre for Fetal Medicine Gennet in Prague. The quality of NT measurements was assessed using the NT retrospective distribution parameters and EWMA charts, and the results were presented to the sonographers during collective meetings.

RESULTS

Overall, 28,928 NT measurements obtained from six sonographers were eligible for the study. Looking at individual EWMA charts, we observed four main outcomes. First, there was a clear improvement in the performance of sonographers with initially poor performances. Second, the performance of sonographers with an initially satisfactory quality was maintained. Third, there was an observed deterioration of the performance without the audits. Last, the sonographers appreciated an unequivocal and straightforward graphical presentation of EWMA curves.

CONCLUSION

EWMA proved to be an efficient and suitable tool for real-time monitoring of NT quality and led to an overall improvement of the sonographers' performance.

Sonologist's characteristics related to a higher quality in fetal nuchal translucency measured in primary antenatal care centers

OBJECTIVE

To assess the quality of nuchal translucency (NT) measurements in primary care and the sonologist's characteristics related with a higher quality.

METHODS

The median NT expressed in multiples of the median (MoM) was calculated for each sonologist of 14 participating antenatal primary care centers of the Catalan Institute of Health. A survey to the sonologists was used to establish variables related to higher-quality measurements.

RESULTS

The median NT MoM obtained in 16 448 NT measurements, performed by 102 sonologists, was 0.94 MoM. NT underestimation was observed in 46% of the sonologists. Underestimation were less frequent among professionals who performed more than 230 ultrasounds per year (26% vs 53%;p = .022), those who completed the online Fetal Medicine Foundation (FMF) course (22% vs 54%; p = .021), and those who were subject to periodic audits (24% vs 56%; p = .021). Underestimation rate decreased from 60%, to 33% and 14% with the increase of the years of experience from less than 5 years, to 6 to 15 years and more than 15 years of experience, respectively (p = .029).

CONCLUSIONS

Higher-quality measurements were demonstrated in sonologists who performed more ultrasounds per year, those with more years of scanning experience, those who completed the online FMF course, and those periodically audited.

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.

An Overview on Prenatal Screening for Chromosomal Aberrations

This article is a review of current and emerging methods used for prenatal detection of chromosomal aneuploidies. Chromosomal anomalies in the developing fetus can occur in any pregnancy and lead to death prior to or shortly after birth or to costly lifelong disabilities. Early detection of fetal chromosomal aneuploidies, an atypical number of certain chromosomes, can help parents evaluate their pregnancy options. Current diagnostic methods include maternal serum sampling or nuchal translucency testing, which are minimally invasive diagnostics, but lack sensitivity and specificity. The gold standard, karyotyping, requires amniocentesis or chorionic villus sampling, which are highly invasive and can cause abortions. In addition, many of these methods have long turnaround times, which can cause anxiety in mothers. Next-generation sequencing of fetal DNA in maternal blood enables minimally invasive, sensitive, and reasonably rapid analysis of fetal chromosomal anomalies and can be of clinical utility to parents. This review covers traditional methods and next-generation sequencing techniques for diagnosing aneuploidies in terms of clinical utility, technological characteristics, and market potential.

Accuracy of nuchal translucency measurement depends on equipment used and its calibration

OBJECTIVES

To determine the effect of different ultrasound machine-probe combinations on nuchal translucency (NT) measurements and to assess how this impacts on the accuracy of the NT-derived component of first-trimester screening for trisomy 21.

METHODS

Sixteen different ultrasound machine-probe combinations were used for axial measurement of 2.0-, 3.0- and 4.0-mm spaced targets in an ultrasound phantom. Differences between the measured and known values were determined. The mean of the axial measurements was used to calculate adjusted risks for trisomy 21, given specific clinical scenarios.

RESULTS

Differences observed using different machine-probe combinations for the 2.0-mm target ranged from 1.8-2.2 mm; for the 3.0-mm target, 2.7-3.2 mm; and for the 4-mm target, 3.7-4.3 mm, and exceeded those due to intraobserver variability. For a fetal crown-rump length of 50.0 mm and NT measurement of 2.0 mm, the maximum/minimum measurements in the fetus of a 40-year-old woman led to derived risks ranging from 1 in 32 (NT, 2.2 mm) to 1 in 189 (NT, 1.8 mm) and in the fetus of a 20-year-old with an NT of 3.0 mm these ranged from 1 in 102 (NT, 3.2 mm) to 1 in 160 (NT, 2.7 mm).

CONCLUSIONS

We have described the effect of machine-probe combinations on small but very precise ultrasound measurements. Such machine-probe combinations led to greater variability than those ascribed to intraobserver differences, and significantly affected the screening risk for the same fixed measurement. This finding has implications for Down syndrome screening algorithms and audit of ultrasound operators. Furthermore, most ultrasound machines are neither calibrated nor specified for measurements of tenths of a mm.

An audit of first trimester ultrasound screening for chromosomal abnormalities

BACKGROUND

Screening for Down syndrome has been funded in New Zealand since 2010 following the report 'Antenatal Down Syndrome Screening in NZ 2007' which identified that the practice of screening using maternal age and/or nuchal translucency (NT) without biochemical markers was unsafe and should not continue.

AIM

This study aimed to assess the quality of the ultrasound component of first trimester screening in a metropolitan population.

METHODS

Over a 5-month period, all available NT scan images for women referred to the Central Region Fetal Medicine Unit for an increased risk at first trimester screening or a fetal abnormality detected at the 20-week ultrasound scan were reviewed according to the Fetal Medicine Foundation (FMF) criteria and utilising the Herman Score. This is the standard which the National Screening Unit (NSU) and Ministry of Health (MOH) have mandated for the ultrasound component of the screening test.

RESULTS

Of the 52 images, 4 (7.7%) studies were considered unacceptable and another 5 (9.6%) were considered intermediate. The mean score was 5.87 of a possible score of 9. Comparisons with Herman's data are presented and discussed.

CONCLUSIONS

This review suggests that there is potential for the quality of the ultrasound component of the first trimester screening component to improve. This would in turn improve the performance of the screening program. We conclude that formal quality control of this screening program is urgently required.