Le contrôle de qualité en échographie prénatale : intérêt de la biométrie

[Evaluation of a measurement tool with real-time display of the standard value for fetal biometrics]

OBJECTIVES

Most of the ultrasound machines include a tool allowing real-time display of the standard value of the biometric measurement being taken. Our hypothesis was that this tool influences the sonographer as measurements are taken, by inducing a normalization, thus a tendency towards the 50th percentile. The objective of this study was to evaluate the impact of a real-time display of the standard value in prenatal ultrasound screening.

METHODS

We conducted an observational, prospective, controlled and open study including all patients who underwent a prenatal ultrasound scan in the 2nd or 3rd trimester at the University Hospitals in Strasbourg between December 2017 and June 2018. Exclusion criteria were the presence of a fetal morphological abnormality or a karyotypic abnormality. The tool being tested was the real-time display on screen of the gestational age, of which the measurement corresponds to the 50th percentile. The measurements were retrospectively transformed into Z-scores. The main end-point was to compare the distribution of Z-scores between the groups.

RESULTS

We included 3551 ultrasound examinations: 696 performed with the tool and 2796 performed without. Fifty-nine scans were excluded due to morphological abnormalities. There was no statistically significant difference between the Z-scores distributions of measurements performed with or without the tool, regardless of the parameter studied. There was also no difference in the detection of pathological measurements: below the 10th percentile or above the 90th percentile.

CONCLUSION

The use of such a tool does not seem to be detrimental to biometric screening, but on the other hand does not seem useful either.

Quality assessment of pelvic ultrasound for uterine myoma according to the CNGOF guidelines

INTRODUCTION

French guidelines regarding the minimum criteria for gynaecological ultrasound were given in a recent report in 2016, by the French National College of Obstetricians and Gynaecologists (CNGOF). An accurate report is essential for the optimal care of women, especially those presenting myomas. The goal of this study was to evaluate the quality of gynaecological ultrasound reports for women with type 0 to 2 uterine myomas, referring to the items contained in the French guidelines.

MATERIALS AND METHODS

A retrospective descriptive study was conducted from reports of ultrasounds performed in private offices and in the gynaecologic department of a hospital, between June 2014 and June 2016 (before the report of CNGOF). These reports involved women who underwent hysteroscopic resection of myoma(s). A search of validated items was conducted for all of the reports, and the missing items were analysed. The different types of practitioners and between hospital and private medical offices were also compared with Chi-square tests.

RESULTS

A total of 138 reports were analysed; 71 were performed in private offices and 67 were performed in the gynaecologic unit of the hospital. Many items were missing in the reports, with disparities between the type of institution (private offices or hospital) and the speciality of practitioners (radiologists or gynaecologists). Specific items regarding myomas, such as the International Federation of Gynaecologists and Obstetricians (FIGO) classification or measurement of the posterior wall, were more often missing in reports from radiologists (89.7% and 79.5%, respectively) than in reports from gynaecologists (21.2% and 34.3%, respectively) (P<0.05). A significant difference was also observed for these data between private offices' reports and hospitals' reports. Items relative to ultrasound structures, such as the appearance of myomas or associated abdominal effusion, were more frequently missing in gynaecologists' reports (88.9% and 49.5%, respectively) compared to radiologists' reports (56.4% and 12.8%, respectively) (P<0.05).

CONCLUSIONS

Certain items are present in all the reports, while others are insufficiently mentioned. These inequalities can be explained in part by the type of practice; however, methods to overcome these difficulties must be developed. Information campaigns to educate professionals on the minimum reporting and training conducted jointly by radiologists and gynaecologist surgeons might improve reports and improve the care of women.

Continuous independent quality control for fetal ultrasound biometry provided by the cumulative summation technique

OBJECTIVE

To apply the cumulative summation (CUSUM) technique for an evaluation of the learning process of sonographic fetal weight estimation at term in combination with the z-scores of biometry determinants and to assess the time of appearance and sources of errors.

METHODS

Learning curve (LC-CUSUM) and double CUSUM charts for systematic error detection based on absolute and signed mean percentage error were generated to retrospectively estimate the longitudinal accuracy of sonographic fetal weight estimation conducted by three trainees and one experienced examiner. For LC-CUSUM analysis an examination was considered to be a failure when there was an absolute error in birth weight estimation >/= 15%. Fetal biometry measurements (head circumference, abdominal circumference (AC) and femur length (FL)) from 227 routine ultrasound scans of one examiner were separately transformed into z-scores and double CUSUM charts were generated to assess the systematic errors for each determinant.

RESULTS

The LC-CUSUM charts revealed that different numbers of scans are required for different examiners to achieve competence in estimating birth weight. AC and FL deviated most significantly from expected values (P < 0.05). The double CUSUM charts revealed exact periods of systematic errors in the measurement of biometry determinants, clearly reflecting errors of fetal weight estimation.

CONCLUSIONS

The use of CUSUM techniques in the analysis of sonographic data allows observation of the development of an examiner's skill and maintenance of competence. The CUSUM technique not only allows the reasons for impaired fetal weight estimation to be revealed but also allows determination of the exact time when inaccurate measurements start to occur. We suggest that CUSUM charts should be implemented in routine clinical practice as a measure of objective quality evaluation of sonographic fetal biometry.

Using Z-scores to compare biometry data obtained during prenatal ultrasound screening by midwives and physicians

OBJECTIVE

To compare retrospectively the distribution of foetal biometry data as measured by midwives and physicians during second and third trimester screening of an unselected population of pregnant women.

METHODS

Standard measurements of biparietal diameter (BPD), head circumference (HC), abdominal circumference (AC), and femur length (FL) were performed by four midwives and ten physicians at 20 to 24 weeks of gestation and at 30 to 34 weeks of gestation as part of routine ultrasound examinations over a 26-month period (Jan. 2005-Mar. 2007). All measurements were converted into Z-scores using different prediction equations. The reference chart best fitting our practice was determined for each fetal parameter (French College of Sonographers for BPD, Chitty et al. for HC and FL, Snidjers and Nicolaides for AC). The means and SDs of the Z-score distributions for data collected by midwives and physicians were compared using Student's t-test for means and the Fisher-Snedecor test for SDs.

RESULTS

We retrieved 1566 and 1631 measurements made by midwives and physicians respectively between 20 and 24 weeks of gestation, and 1710 and 1578 measurements made by midwives and physicians respectively between 30 and 34 weeks of gestation. Mean values recorded by midwives were significantly closer to 0 (p < 0.05) for many foetal parameters. SD values were also significantly lower and were below 1.

CONCLUSION

In this study, midwives have a greater tendency than physicians to normalize biometry data. Such normalization may hamper the sensitivity of routine ultrasound screening for abnormal foetal growth.