Nuchal translucency thickness measurement: repeatability using a virtual ultrasound scanner

A prospective study to assess the clinical impact of interobserver reliability of sonographic measurements of fetal nuchal translucency and crown-rump length on combined first-trimester screening

OBJECTIVE:

To examine the interobserver variability for fetal biometric parameters and to focus on how this variability affects the combined first-trimester screening test results.

METHODS:

Sixty-four singleton pregnancies who were scheduled for combined first-trimester screening were investigated. Two experienced sonographers performed all examinations at the same visit. The risk calculations of screening were performed according to the each operator’s individual ultrasonographic fetal measurements. Interobserver variability in measurements of fetal nuchal translucency (NT) and crown-rump length (CRL) and the effect of this interobserver variability on the screening results were assessed.

RESULTS:

Interobserver reliabilities for NT and CRL were 0.687 and 0.945 (p<0.001), respectively. Interobserver reliability coefficients for trisomy 21 and trisomy 13/18 were 0.945 and 0.963 (p<0.001), respectively.

CONCLUSION:

Our study demonstrated quite high interobserver reliability for CRL measurement, while interobserver agreement for NT was lower. Despite this lower reliability and agreement for NT measurement, interobserver reliability for chromosomal abnormalities was quite high.

Clinical Simulation in Modern Teaching and Training of Sonography in Obstetrics and Gynecology

Advances in computer technology, hardware and software have made ultrasound a diagnostic imaging technique of choice in certain areas of medicine or specialties such as obstetrics and gynecology. In teaching and training of obs/gyne ultrasonography, medical educators can utilize different forms of clinical simulators: traditional standardized patients and standard ultrasound diagnostic equipment, computer-based simulators, ultrasound simulators or ultrasound simulators with manikins. The popularity of a simulator is determined not only by its features, ease of use and cost, but also by its available learning modules and applications.

Technology in ultrasound and computers are rapidly advancing in enhancing the quality and miniaturizing ultrasound machines. Portable and handheld ultrasound equipments are quickly becoming indispensable diagnostic instruments in different health care settings especially the emergency rooms and physician offices. Concerns, however, remain related to the lack of competence of health care providers in using and interpreting results of ultrasound studies, and the needs to standardize the training in ultrasonography. It is important to have access to one or more ultrasound simulators; however, it is even more important to establish and integrate fundamental structure of training ultrasonography into the main training curriculum of undergraduate, graduate, and postgraduate medical education.

Variability of Nuchal Translucency Measurement

OBJECTIVES

To evaluate intra- and inter-observer variations of nuchal translucency (NT) measurements and study the duration of measurements.

SUBJECTS

One hundred and forty-seven singleton pregnant women with 10-14 weeks of gestation who had attended antenatal clinic during January 1st, 2000-August 31st, 2001 were included.

METHODS

Crown-rump length and NT were measured three times for each woman. Then, another examiner who was unaware of the previous results did the other three measurements. The duration of measurements was recorded. Intra-observer and inter-observer variations were analyzed by repeated ANOVA and paired t test, respectively. The correlation of NT measurements within each observer and between paired observers was evaluated by intraclass correlation coefficients (ICC). Kappa statistic was calculated for agreement.

RESULTS

Intra-observer variation of all 10 examiners at three institutes was varied from 0.20 +/- 0.27 to 0.33 +/- 0.41 mm. Inter-observer variation at Chiang Mai University was 0.40 +/- 0.37 mm which was the highest value compared with those at Prince of Songkla and Khon Kaen University (p < 0.05). The mean duration of measurements was in range of 8-12 min. The intra-observer repeatability of the first two measurements showed ICCs varying from 0.61 to 0.94. The inter-observer repeatability of paired examiners showed a variation in ICC from 0.28-0.90. The kappa value expressing the intra- and inter-observer repeatability as being >95th or < or = 95th percentile was 0.73 and 0.72, respectively.

CONCLUSIONS

NT measurement was reproducible for small variation and good agreement. The duration of measurements was acceptable.

Audit on nuchal translucency thickness measurements in Flanders, Belgium: a plea for methodological standardization

OBJECTIVES

To audit nuchal translucency thickness (NT) measurements for fetal aneuploidy screening in Flanders, and to estimate the impact of small variations in NT measurement on the screening result of two first-trimester screening algorithms: maternal age + NT (Algorithm A), and maternal age + NT + pregnancy associated plasma protein-A + free beta-human chorionic gonadotropin (Algorithm B).

METHODS

We used the database of first-trimester combined screening, as collected by the General Medical Laboratory AML in Antwerp, Belgium, between 1 January 2001 and 1 April 2004. Audit was performed by establishing a delta-NT distribution curve for one trainee of The Fetal Medicine Foundation (FMF) and for a group of 263 other sonographers, in comparison with the FMF reference values. Risks for fetal aneuploidy were calculated at a cut-off value of 1 : 300 for Algorithm A and 1 : 150 for Algorithm B. These risks were recalculated in both algorithms after a modeled increase of all NT values by 0.1 or 0.2 mm.

RESULTS

In a total of 592 measurements performed by the FMF trainee, the 5th, 50th and 95th percentiles of delta-NT measurements were at -0.41, +0.03 and +0.68 mm, respectively. These values were close to the FMF reference values. The screen-positive rate for this set of data was 4.4% (26/592) in both algorithms. For the 12 555 measurements of the 263 other sonographers, the 5th, 50th and 95th percentiles of delta-NT were at -0.81, -0.14 and +0.73 mm, respectively, which clearly indicates underestimation of NT in the lower range. In this set of data the screen-positive rate was 3.5% for both algorithms (439/12 555 for Algorithm A and 436/12 555 for Algorithm B). Also in this group, 5% (59/1186) of negative screening results at maternal age > or = 35 years in Algorithm A became positive after a modeled 0.1-mm increase in NT, whereas this was only in 1.2% (134/11 369) of tests at maternal age < 35 years (P < 0.0001). The overall increase of screen-positive rate in Algorithm A after an NT modification of +0.1 mm was 1.2% (152/12 555), significantly more than in Algorithm B (86/12 555; 0.7%) (P < 0.0001).

CONCLUSION

In Flanders, there is a systematic underestimation of NT in comparison with the FMF reference range. Attempts to change these measurements according to the FMF criteria are crucial. This will mainly influence the screening results of women at advanced maternal age and of NT-based algorithms without the use of other parameters.

Ultrasound simulators: experience with the SonoTrainer and comparative review of other training systems

Ultrasound has become indispensable in prenatal diagnosis. Ultrasound training, however, still lacks proper quality assessment and control. Moreover, most fetal anomalies which must be diagnosed during pregnancy are extremely rare. Ultrasound simulators could provide an opportunity to overcome this dilemma. This review summarizes the potential benefits of simulator-based ultrasound training, briefly describes the properties of a variety of ultrasound simulators that have been developed for various applications including prenatal diagnosis, and presents the SonoTrainer sonography simulation system which makes it possible to run a real-time simulation of a complete prenatal ultrasound examination. We evaluated the system for the training of first- and second-trimester screening for both normal and pathological findings and found that physicians who received theoretical training and were additionally trained with the simulator (T + S) significantly improved their skills in measurements of nuchal translucency thickness (NT) and crown-rump length (CRL) as compared with colleagues who only underwent theoretical instruction (T) [mean +/- SD NT deviation: 0.31 +/- 0.1 mm (T + S) vs. 0.62 +/- 0.2 mm (T), P < 0.05; mean +/- SD CRL deviation: 1.48 +/- 2.0 mm (T + S) vs. 3.27 +/- 2.5 (T), P < 0.05]. Simulator-based training enabled physicians to diagnose rare fetal anomalies in the second trimester with a sensitivity of 86% and a specificity of 100%. In a study in which second-trimester scans including fetal anomalies were presented to physicians, 96% of the participants subjectively estimated their training effect as being good. We therefore conclude that simulator-based training would provide an ideal educational tool to test, improve and monitor a physician's or technician's ultrasound skills in detecting fetal anomalies.