Quality assessment of routine nuchal translucency measurements: a North American laboratory perspective

How much can AI see in early pregnancy: A multi-center study of fetus head characterization in week 10-14 in ultrasound using deep learning

PURPOSE

To investigate if artificial intelligence can identify fetus intracranial structures in pregnancy week 11-14; to provide an automated method of standard and non-standard sagittal view classification in obstetric ultrasound examination METHOD AND MATERIALS: We proposed a newly designed scheme based on deep learning (DL) - Fetus Framework to identify nine fetus intracranial structures: thalami, midbrain, palate, 4th ventricle, cisterna magna, nuchal translucency (NT), nasal tip, nasal skin, and nasal bone. Fetus Framework was trained and tested on a dataset of 1528 2D sagittal-view ultrasound images from 1519 females collected from Shenzhen People's Hospital. Results from Fetus Framework were further used for standard/non-standard (S-NS) plane classification, a key step for NT measurement and Down Syndrome assessment. S-NS classification was also tested with 156 images from the Longhua branch of Shenzhen People's Hospital. Sensitivity, specificity, and area under the curve (AUC) were evaluated for comparison among Fetus Framework, three classic DL models, and human experts with 1-, 3- and 5-year ultrasound training. Furthermore, 4 physicians with more than 5 years of experience conducted a reader study of diagnosing fetal malformation on a dataset of 316 standard images confirmed by the Fetus framework and another dataset of 316 standard images selected by physicians. Accuracy, sensitivity, specificity, precision, and F1-Score of physicians' diagnosis on both sets are compared.

RESULTS

Nine intracranial structures identified by Fetus Framework in validation are all consistent with that of senior radiologists. For S-NS sagittal view identification, Fetus Framework achieved an AUC of 0.996 (95%CI: 0.987, 1.000) in internal test, at par with classic DL models. In external test, FF reaches an AUC of 0.974 (95%CI: 0.952, 0.995), while ResNet-50 arrives at AUC∼0.883, 95% CI 0.828-0.939, Xception AUC∼0.890, 95% CI 0.834-0.946, and DenseNet-121 AUC∼0.894, 95% CI 0.839-0.949. For the internal test set, the sensitivity and specificity of the proposed framework are (0.905, 1), while the first-, third-, and fifth-year clinicians are (0.619, 0.986), (0.690, 0.958), and (0.798, 0.986), respectively. For the external test set, the sensitivity and specificity of FF is (0.989, 0.797), and first-, third-, and fifth-year clinicians are (0.533, 0.875), (0.609, 0.844), and (0.663, 0.781), respectively.On the fetal malformation classification task, all physicians achieved higher accuracy and F1-Score on Fetus selected standard images with statistical significance (p < 0.01).

CONCLUSION

We proposed a new deep learning-based Fetus Framework for identifying key fetus intracranial structures. The framework was tested on data from two different medical centers. The results show consistency and improvement from classic models and human experts in standard and non-standard sagittal view classification during pregnancy week 11-13+6.

CLINICAL RELEVANCE/APPLICATION

With further refinement in larger population, the proposed model can improve the efficiency and accuracy of early pregnancy test using ultrasound examination.

United States' experience in nuchal translucency measurement: variation according to provider characteristics in over five million ultrasound examinations

OBJECTIVE

The Nuchal Translucency Quality Review (NTQR) program has provided standardized education, credentialing and epidemiological monitoring of nuchal translucency (NT) measurements since 2005. Our aim was to review the effect on NT measurement of provider characteristics since the program's inception.

METHODS

We evaluated the distribution of NT measurements performed between January 2005 and December 2019, for each of the three primary performance indicators of NT measurement (NT median multiples of the median (MoM), SD of log₁₀ NT MoM and slope of NT with respect to crown-rump length (CRL)) for all providers within the NTQR program with more than 30 paired NT/CRL results. Provider characteristics explored as potential sources of variability included: number of NT ultrasound examinations performed annually (annual scan volume of the provider), duration of participation in the NTQR program, initial credentialing by an alternative pathway, provider type (physician vs sonographer) and number of NT-credentialed providers within the practice (size of practice). Each of these provider characteristics was evaluated for its effect on NT median MoM and geometric mean of the NT median MoM weighted for the number of ultrasound scans, and multiple regression was performed across all variables to control for potential confounders.

RESULTS

Of 5 216 663 NT measurements from 9340 providers at 3319 sites, the majority (75%) of providers had an NT median MoM within the acceptable range of 0.9-1.1 and 85.5% had NT median MoM not statistically significantly outside this range. Provider characteristics associated with measurement within the expected range of performance included higher volume of NT scans performed annually, practice at a site with larger numbers of other NT-credentialed providers, longer duration of participation in the NTQR program and alternative initial credentialing pathway.

CONCLUSIONS

Annual scan volume, duration of participation in the NTQR program, alternative initial credentialing pathway and number of other NT-credentialed providers within the practice are all associated with outcome metrics indicating quality of performance. It is critical that providers participate in ongoing quality assessment of NT measurement to maintain consistency and precision. Ongoing assessment programs with continuous feedback and education are necessary to maintain quality care. © 2021 International Society of Ultrasound in Obstetrics and Gynecology.

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.

Quality control of ultrasonography markers for Down's syndrome screening: a retrospective study by the laboratory

OBJECTIVES

Quality control of ultrasonography markers is necessary to ensure greater efficacy of prenatal aneuploidy screening. The aim of this study was to assess the quality of the crown-rump length (CRL) and nuchal translucence (NT) measurement accuracy by the laboratory according to quality indicators.

METHODS

Retrospective observational study on 4,908 single-foetus pregnant women who underwent prenatal aneuploidy screening in the first trimester of pregnancy. Euploid foetuses with CRL between 45 and 84 mm were included, while those with NT≥3.5 mm were excluded. CRL measurement was considered to be accurate if the median multiples of the median (MoM) for pregnancy-associated plasma protein A (PAPP-A) was between 0.90 and 1.10. Fifteen sonographers participated in the study, six of whom comprised the control group. Systematic error for a sonographer was considered when CRL measurement was greater than ±2 mm with respect to the control group. Quality for NT was assured by means of the WHIRI method and each sonographer cumulative sum control chart (CUSUM).

RESULTS

For CRL accuracy, five sonographers underestimated the measurements, while another four overestimated them, with no statistical differences. For smaller sized foetuses, all sonographers met the established specifications. Regarding NT control, three sonographers did not meet the quality criteria for the median MoM. All sonographers met the specifications for the logarithmic standard deviation of the NT MoM levels. Thirteen sonographers met the CUSUM specifications.

CONCLUSIONS

Evaluation of a quality control of ultrasonography parameters by laboratory professionals is necessary to avoid under- or overestimation tendencies for CRL and NT measurements. CUSUM is a useful tool for the immediate correction of errors in NT measurements.

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.

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.

Impact of Including or Removing Nuchal Translucency Measurement on the Detection and False-Positive Rates of First-Trimester Down Syndrome Screening

INTRODUCTION

First-trimester Down syndrome (DS) screening combining maternal age, serum markers (pregnancy-associated plasma protein-A and beta-human chorionic gonadotropin) and nuchal translucency (NT) gives an 85% detection rate for a 5% false-positive rate. These results largely depend on quality assessment of biochemical markers and of NT. In routine practice, despite an ultrasound quality control organization, NT images can be considered inadequate. The aim of the study was to evaluate the consequences for risk calculation when NT measurement is not taken into account.

MATERIAL AND METHOD

Comparison of detection and false-positive rates of first-trimester DS screening (PerkinElmer, Turku, Finland), with and without NT, based on a retrospective study of 117,126 patients including 274 trisomy 21-affected fetuses. NT was measured by more than 3,000 certified sonographers.

RESULTS

There was no significant difference in detection rates between the two strategies including or excluding NT measurement (86.7 vs. 81.8%). However, there was a significant difference in the false-positive rates (2.23 vs. 9.97%, p < 0.001).

DISCUSSION

Sonographers should be aware that removing NT from combined first-trimester screening would result in a 5-fold increase in false-positive rate to maintain the expected detection rates. This should be an incentive for maintaining quality in NT measurement.

Do the Levels of Maternal Plasma Trace Elements Affect Fetal Nuchal Translucency Thickness?

OBJECTIVE

Fetal nuchal translucency (NT) thickness is an important marker for prenatal screening; however, studies focusing on the correlation between maternal trace element levels and NT thickness are limited. The aim of this study was to evaluate maternal trace element levels during the first trimester and to investigate the association between maternal trace element levels and fetal NT thickness.

METHODS

In total, 113 samples were obtained from singleton pregnant women. Maternal plasma samples were collected in the first trimester of gestation. Plasma trace element levels were measured using Inductively Coupled Plasma Mass Spectrometry (ICP-MS). Nuchal translucency thickness was measured using ultrasonography at 10-14 weeks of gestation.

RESULTS

We found that maternal plasma potassium (K) levels had a significant negative correlation with both NT (r = -0.230, p < 0.05) and NT Multiples of the Median (NT MoM) (r = -0.206, p < 0.05). After adjustment for potential confounders, log-transformed maternal plasma potassium levels in the first trimester were significantly associated with fetal NT (NT MoM: β = -0.68, p < 0.05; NT: β = -1.20, p < 0.01). Although not statistically significant, the As, Hg and Pb levels in maternal plasma were positively correlated with NT, and the Mg, Cu, Zn, Na and Ca levels were negatively correlated with NT.

CONCLUSION

Maternal plasma K levels during the first trimester appeared to be associated with NT thickness. The essential elements tended to decrease NT thickness, and non-essential elements tended to increase it.

Nuchal Translucency Quality Review (NTQR) program: first one and half million results

OBJECTIVE

To evaluate the performance of first-trimester nuchal translucency (NT) measurement by providers (physician-sonologists and sonographers) within the Nuchal Translucency Quality Review (NTQR) program.

METHODS

After training and credentialing providers, the NTQR monitored performance of NT measurement by the extent to which an individual's median multiple of the normal median (MoM) for crown-rump length (CRL) was within the range 0.9-1.1 MoM of a published normal median curve. The SD of log10 MoM and regression slope of NT on CRL were also evaluated. We report the distribution between providers of these performance indicators and evaluate potential sources of variation.

RESULTS

Among the first 1.5 million scans in the NTQR program, performed between 2005 and 2011, there were 1 485 944 with CRL in the range 41-84 mm, from 4710 providers at 2150 ultrasound units. Among the 3463 providers with at least 30 scans in total, the median of the providers' median NT-MoMs was 0.913. Only 1901 (55%) had a median NT-MoM within the expected range; there were 89 above 1.1 MoM, 1046 at 0.8-0.9 MoM, 344 at 0.7-0.8 MoM and 83 below 0.7 MoM. There was a small increase in the median NT-MoM according to providers' length of time in the NTQR program and number of scans entered annually. On average, physician-sonologists had a higher median NT-MoM than did sonographers, as did those already credentialed before joining the program. The median provider SD was 0.093 and the median slope was 13.5%. SD correlated negatively with the median NT-MoM (r = -0.34) and positively with the slope (r = 0.22).

CONCLUSION

Even with extensive training, credentialing and monitoring, there remains considerable variability between NT providers. There was a general tendency towards under-measurement of NT compared with expected values, although more experienced providers had performance closer to that expected.

Repeat measurements of nuchal translucency at 11-14 weeks of gestation: when do we need them?

OBJECTIVE

Previous studies have recommended that several repeat measurements of nuchal translucency (NT) be obtained to optimize sensitivity of the screening process. However, truncation is applied within the risk calculation for small NT measurements; therefore, repeating NT measurements in the lower range may be unnecessary. The aim of this study was to determine the optimal number of NT measurements and whether this is dependent on the initial value obtained.

METHODS

We simulated the expected distribution of sets of five repeat NT measurements and their corresponding likelihood ratios (LR) for a variety of crown-rump length (CRL) values at 11-14 weeks' gestation, based on the published mixture model for first-trimester NT measurements and on published data regarding NT measurement variability. The ratio between LR obtained from the highest and the initial measurement in each set were computed, with a ratio of 1 indicating that repeat measurements would have no effect on risk estimation. We calculated NT cut-offs below which a change in estimated LR would occur in fewer than 10% of cases if repeat measurements were obtained, and we tested this approach on a real first-trimester screening dataset.

RESULTS

The simulations performed indicated that repeating NT measurements when the first NT obtained ranged between ≤ 0.9 and ≤ 1.6 mm at CRLs of 45 and 84 mm, respectively, is not useful. When applied to a real dataset, our approach allowed avoiding repetition of measurements in 47/165 cases (28%).

CONCLUSIONS

Although there is some variability in NT measurements, repeat assessment is not useful to optimize screening performance for the smallest NT measurements due to lower truncation limits that are applied in risk calculation. Our study provides NT cut-off values, in relation to CRL, below which it appears that there is no need to repeat measurements once a good quality image has been obtained.

Cumulative sum plots and retrospective parameters in first-trimester ductus venosus quality assurance

OBJECTIVE

This study aimed to evaluate the application of two quality assurance methods to the ductus venosus pulsatility index (DVPI), as a first-trimester aneuploidy marker, including retrospective assessment of distribution parameters and cumulative sum (CUSUM) plots.

METHODS

The DVPI was measured in 14 444 singleton fetuses at 11+0 to 13+6 weeks in two Fetal Medicine centers during a 4-year period. Sonologist-specific quality assurance distribution parameters, previously described for nuchal translucency, were assessed: the median multiples of the median (MoM), the logarithmic standard deviation of DVPI MoMs and the weekly DVPI percent decrease. Quality assurance results were compared between median MoMs and MoM-based CUSUM plots.

RESULTS

When sonologist-specific DVPI distribution parameters were retrospectively applied for quality assurance, a 1.0 median MoM, a 0.1 median logarithmic standard deviation and a 3.4 median weekly DVPI drop percentage were observed. CUSUM plots showed good agreement with 0.9-1.1 MoMs range for median MoM, in the assessment of sonologist-specific performances.

CONCLUSION

Retrospective and prospective DVPI quality assurance methods appear to be applicable to DVPI at 11+0 to 13+6 weeks. Its use should be encouraged if DVPI is to be added to first-trimester Down syndrome or cardiac defects screening.

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

Objective. Quantitative analysis of the quality of nuchal translucency (NT) measurements. Methods. First-trimester combined screening for Down syndrome was performed to all pregnant women attended in our Department from October 2003 to November 2009. NT was measured according to the Fetal Medicine Foundation (FMF) criteria by 20 trained obstetricians. The performance of NT measurements was retrospectively analyzed with regard to several quality control standards. Accuracy according to experience, professional profile, crown rump length (CRL) values, and FMF certification was statistically tested. Results. A total of 14978 NT measurements were assessed. (1) The mean operator-specific median NT-MoM values was 0,98. (2) Mean percentage of cases >95th and <5th centiles were 5,0% and 4,2%, respectively. (3) Logarithmic mean and SD of the NT MoM values were 0,00 and 0,13, respectively. (4) The DR for trisomy 21 at screening time was 90,7% for a FPR of 6,7% for standard screening strategy. (5) According to Cumulative SUM (CUSUM) figures, the performance was more acceptable in FMF-certified operators. Conclusion. Overall, quality standards show optimal NT measurements in our unit. Operator experience, a dedicated profile to fetal medicine, CRL over 60 mm, and FMF certification have a significant positive impact on the quality standards.

Modeling Down syndrome screening performance using first-trimester serum markers

OBJECTIVE

To evaluate the modeled predictive value of three current screening markers (pregnancy-associated plasma protein-A (PAPP-A), free β-human chorionic gonadotropin (free β-hCG), and nuchal translucency (NT)) and four potential screening markers (a disintegrin and metalloprotease 12 (ADAM12), total hCG, placental protein 13 (PP13), and placental growth factor (PlGF)) for Down syndrome using different screening strategies.

METHODS

All markers were measured in stored first-trimester serum of 151 Down syndrome cases and 847 controls. All marker levels were expressed as gestational age-specific multiples of the median (MoMs) and comparisons were made using the Mann-Whitney U-test. Detection rates (DRs) for fixed false-positive rates (FPRs) were modeled using different screening strategies.

RESULTS

Significantly different median MoMs for Down syndrome cases compared to controls were found for PAPP-A (0.49 vs. 1.00; P < 0.0001), free β-hCG (1.70 vs. 1.01; P < 0.0001), ADAM12 (0.89 vs. 1.00; P < 0.0001), total hCG (1.28 vs. 1.00; P < 0.0001), PlGF (0.80 vs. 1.00; P < 0.0001) and NT (1.74 vs. 1.01; P < 0.0001). The lower PP13 MoM in Down syndrome cases (0.91 vs. 1.00) was not statistically significant (P = 0.061). Adding the four new markers to the current screening strategy (i.e. first-trimester combined test) led to an increase in DR from 77% to 80% at a 5% FPR. The modeled application of a two-sample screening strategy (with some markers assessed early and others later in the first trimester) increased the DR to 89%. In a two-step contingent screening model, using an intermediate risk range of 1 in 100 to 1 in 2000 at biochemical screening (using all markers), the overall DR was 77%, but it was predicted that only 33% of women would require referral for NT measurement.

CONCLUSIONS

First-trimester Down syndrome screening may be improved by adding new markers to the current screening test and by applying different screening strategies. The application of a two-sample screening model resulted in the highest predicted DR, but this should be confirmed in population-based prospective studies.

The CUSUM test applied in prospective nuchal translucency quality review

OBJECTIVES

To design a cumulative sum (CUSUM) test for prospective nuchal translucency (NT) measurement quality review that is as stringent as the retrospective quality review methods based on distribution parameters currently in use.

METHODS

The database including all fetal NT measurements obtained during a 2-year period in a single center was reviewed, and measurements obtained by sonologists who measured fewer than 100 cases were excluded. The NT distribution parameters proposed by The Fetal Medicine Foundation (FMF) and the Women & Infants Hospital of Rhode Island (WIHRI) were assessed in the whole NT series and in sonologist-specific distributions. A previously described CUSUM model was adapted to fulfil our objective.

RESULTS

Two thousand four hundred and seventy-five NT measurements were obtained by seven sonologists during the study period (January 2007-December 2008). In the assessment of sonologist-specific NT distributions, two sonologists fulfilled all the FMF and WIHRI criteria, one showed NT overestimation and four failed due to NT underestimation. Our new CUSUM test model, based on multiples of the median deviations, showed good agreement with the FMF and WIHRI methods in the assessment of sonologist-specific performance.

CONCLUSIONS

Our CUSUM test model showed close agreement with the retrospective quality review methods based on distribution parameters currently in use, but with the advantage that it can be applied prospectively, allowing for earlier correction of deviations from target performance.

Likelihood ratio-based quality control for nuchal translucency measurements at 11-14 weeks of gestation

OBJECTIVE

To develop a quantitative quality control process of nuchal translucency (NT) measurement at 11-14 weeks of gestation based on the mixture model, characterized by analysis of the corresponding distribution of the likelihood ratio (LR).

METHODS

Based on the published mixture model for NT measurement in the first trimester, we simulated the expected distribution of NT and the corresponding LR. This approach was then tested for the quality control of 15 048 NT measurements performed by four operators trained and certified by The Fetal Medicine Foundation. The new quality control approach based on LR was compared with existing processes based on NT plots, multiples of the median (MoMs) and analysis of the 95(th) centile.

RESULTS

Each operator contributed 2176-4730 examinations. Median, 5(th) and 95(th) centile of NT values ranged from 1.4 to 1.6, 1.0 to 1.0 and 2.2 to 2.6 mm, respectively. Median of NT-MoM values ranged from 0.83 to 0.95. Analysis of the distribution of NT measurements confirmed departure from the assumptions of the delta-NT and NT-MoM models. Analysis of LR distributions demonstrated a significant difference between observed and expected distributions for all operators (P < 10(-4) ).

CONCLUSION

An LR-based quality control process is feasible at 11-14 weeks of gestation. Because it is more sensitive to measurement bias around the critical area of the 95(th) centile, its use should be encouraged.

Analysis of Quality of Nuchal Translucency Measurements

Objective

Quantitative analysis of the quality of nuchal translucency (NT) measurements.

Methods

This is a retrospective single-center study. NT was measured according to the Fetal Medicine Foundation (FMF) criteria by 20 trained obstetricians (October 2003-November 2009). The performance of NT measurements was analyzed with regard to several quality control standards. Accuracy according to experience, professional profile, crown-rump length (CRL) values and FMF certification was statistically tested.

Results

A total of 14,978 NT measurements were assessed. (1) The mean operator-specific median NT-MoM values was 0.98. (2) Mean percentage of cases >95th and <5th percentiles were 5.0 and 4.2% respectively. (3) Logarithmic mean and SD of the NT-MoM values were 0.00 and 0.13 respectively. (4) The DR for trisomy 21 at screening time was 90.7% for a FPR of 6.7% for standard screening strategy. (5) According to cumulative SUM (CUSUM) figures, the performance was more acceptable in FMF-certified operators. Operator experience, exclusive dedication to FM, FMF certification and a range of CRL values > 60 mm had a statistical impact improving these standards.

Conclusion

Overall quality standards show optimal NT measurements in our unit. Experience a dedicated profile to fetal medicine ultrasound, CRL over 60 mm and FMF certification has a significant positive impact on the quality standards.

Four years' experience with an interlaboratory comparison program involving first-trimester markers of Down syndrome

CONTEXT

We initiated a voluntary, self-funded interlaboratory comparison program in the fall of 2005 because no proficiency testing program was available to laboratories in North America offering first-trimester, combined serum and ultrasound, Down syndrome screening. Objectives.-To evaluate the first 4 years of the interlaboratory comparison program against stated goals, to identify areas of concern, and to create new initiatives as indicated.

DESIGN

Five serum samples are distributed 3 times a year to be tested for pregnancy-associated plasma protein A, human chorionic gonadotropin or its β subunit, and dimeric inhibin-A; participants convert these results into multiples of the median. Patient histories include nuchal translucency information that enables the calculation of the risk of Down syndrome. Also included are educational components linked to interlaboratory comparison program results. Assessment of integrated (first- and second-trimester markers) risks is accomplished by having participants combine interlaboratory comparison program results with their results from a second-trimester proficiency testing program administered by the College of American Pathologists.

RESULTS

The precision profile for pregnancy-associated plasma protein A shows decreasing coefficients of variation with increasing pregnancy-associated plasma protein A concentrations and multiples of the median (25% to 11% and 30% to 15%, respectively). In contrast, coefficients of variation are a relatively constant 12% throughout the entire range of human chorionic gonadotropin results. On a logarithmic scale, the median coefficient of variation of the risk of Down syndrome is 9%.

CONCLUSIONS

Participants in the interlaboratory comparison program reliably measure analytes, compute multiples of the median, and calculate consistent Down syndrome risks. Assays for the measurement of pregnancy-associated plasma protein A are not standardized and are less precise than those for human chorionic gonadotropin. Participants calculate reliable median equations given sonographer-specific sets of paired crown-rump length and nuchal translucency measurements.

Bead-based multiplexed immunoassays to identify new biomarkers in maternal serum to improve first trimester Down syndrome screening

OBJECTIVES

To identify new discriminative biomarkers for Down syndrome (DS) pregnancies using a bead-based multiplexed immunoassay, and to use the newly identified biomarkers to construct a prediction model for non-invasive DS screening.

METHODS

Maternal serum samples of 14 DS pregnancies and 15 matched controls were analyzed with a bead-based multiplexed immunoassay containing immunoassays for 90 different analytes. Potential biomarkers were selected on the basis of concentration fold ratios between DS and control samples. For these markers and the current screening markers (pregnancy-associated plasma protein-A, PAPP-A; free beta subunit of human chorion gonadotrophin (fbeta-hCG) and nuchal translucency) prediction values were obtained and used to calculate detection rates (DR) at a 5% false positive rate.

RESULTS

Seven potential biomarkers of which the fold ratio exceeded 1.3 or -1.3 were selected for further analysis. All 14 DS cases in this study were detected using the combination of all currently used and newly identified markers. The modelled DR for all markers extrapolated to the general pregnant population was 82.5%, compared to a modelled DR of 56.2% for the current screening markers.

CONCLUSION

This study demonstrates the possibility of improving the performance of the current first-trimester DS screening by addition of new biomarkers, which were identified using bead-based multiplexed immunoassays.

Quality of nuchal translucency measurements in The Netherlands: a quantitative analysis

OBJECTIVE

The Dutch Centre for Population Research has specified quality demands for nuchal translucency (NT) measurement in The Netherlands. We performed an analysis of the quality of NT measurement in 2005-2006 and its influence on screening performance.

METHODS

This was a retrospective study of records of NT measurements (n = 27,738) obtained between January 2005 and December 2006 retrieved from the Dutch National Institute for Public Health and the Environment (RIVM). The performance of each individual operator was analyzed with regard to the quality standards, which involved calculation of operator-specific median NT-multiples of the median (MoM) values. For the entire population of operators, a curve was determined describing the relationship between crown-rump length and NT. Detection rates (DR) and false-positive rates (FPR) for Down syndrome were modeled with this new curve and compared to those originally obtained using previously published reference data.

RESULTS

Only 22% of all operators met the quality requirement of performing more than 150 NT measurements per year. However, no relationship was found between the number of measurements per operator and their median NT-MoM. The mean of all operator-specific median NT-MoM values was 0.94 (target value 1.0). Overall, operators with The Fetal Medicine Foundation certificate measured a significantly higher median NT-MoM (mean of operator-specific medians, 0.98) as compared to the non-certified operators (0.92). During the study period, the monthly median NT-MoM of all operators rose steadily, from 0.86 in January 2005 to 0.96 in December 2006. Recalculation of the risk for Down syndrome after adjusting the reference NT medians using our own data led to a modeled 4% increase in DR at a 5% FPR.

CONCLUSION

Improved monitoring of NT measurement put into effect during the study period seems to have led to an improvement in the accuracy of measurements. Strict quality demands, continued monitoring and scrupulous evaluation of individual operators is likely to lead to an even better performance.

Maintaining quality assurance for sonographic nuchal translucency measurement: lessons from the FASTER Trial

OBJECTIVE

To evaluate nuchal translucency measurement quality assurance techniques in a large-scale study.

METHODS

From 1999 to 2001, unselected patients with singleton gestations between 10 + 3 weeks and 13 + 6 weeks were recruited from 15 centers. Sonographic nuchal translucency measurement was performed by trained technicians. Four levels of quality assurance were employed: (1) a standardized protocol utilized by each sonographer; (2) local-image review by a second sonographer; (3) central-image scoring by a single physician; and (4) epidemiological monitoring of all accepted nuchal translucency measurements cross-sectionally and over time.

RESULTS

Detailed quality assessment was available for 37 018 patients. Nuchal translucency measurement was successful in 96.3% of women. Local reviewers rejected 0.8% of images, and the single central physician reviewer rejected a further 2.9%. Multivariate analysis indicated that higher body mass index, earlier gestational age and transvaginal probe use were predictors of failure of nuchal translucency measurement and central image rejection (P = 0.001). Epidemiological monitoring identified a drift in measurements over time.

CONCLUSION

Despite initial training and continuous image review, changes in nuchal translucency measurements occur over time. To maintain screening accuracy, ongoing quality assessment is needed.