Optimal caliper placement: manual vs automated methods

OBJECTIVE

To examine the inter- and intra-operator repeatability of manual placement of callipers in the assessment of basic biometric measurements and to compare the results to an automated calliper placement system.

METHODS

Stored ultrasound images of 95 normal fetuses between 19 and 25 weeks' gestation were used. Five operators (two experts, one resident and two students) were asked to measure the BPD, OFD and FL two times manually and automatically. For each operator, intra-operator repeatability of the manual and automated measurements was assessed by within operator standard deviation. For the assessment of the interoperator repeatability, the mean of the four manual measurements by the two experts was used as the gold standard.The relative bias of the manual measurement of the three non-expert operators and the operator-independent automated measurement were compared with the gold standard measurement by means and 95% confidence interval.

RESULTS

In 88.4% of the 95 cases, the automated measurement algorithm was able to obtain appropriate measurements of the BPD, OFD, AC and FL. Within operator standard deviations of the manual measurements ranged between 0.15 and 1.56, irrespective of the experience of the operator.Using the automated biometric measurement system, there was no difference between the measurements of each operator. As far as the inter-operator repeatability is concerned, the difference between the manual measurements of the two students, the resident, and the gold standard was between -0.10 and 2.53 mm. The automated measurements tended to be closer to the gold standard but did not reach statistical significance.

CONCLUSION

In about 90% of the cases, it was possible to obtain basic biometric measurements with an automated system. The use of automated measurements resulted in a significant improvement of the intra-operator but not of the inter-operator repeatability, but measurements were not significantly closer to the gold standard of expert examiners.

The cavum septi pellucidi in euploid and aneuploid fetuses

OBJECTIVE

To examine whether the cavum septi pellucidi (CSP) is larger in second- and third-trimester fetuses with chromosomal abnormalities than in euploid fetuses.

METHODS

This was a retrospective study utilizing stored two-dimensional images of second- and third-trimester fetuses between 18 and 40 weeks' gestation from three centers in Germany. The width of the CSP was measured by placing the calipers on the inner portion of its lateral borders. Two operators, both of whom were blinded to the fetal karyotype and to the measurements obtained by the other, measured the CSP width. The normal range in euploid fetuses was computed based on the biparietal diameter (BPD) by applying univariate regression analysis. The CSP width in euploid and aneuploid fetuses was transformed into Z-scores and compared using Student's t-test. Univariate regression analysis was used to determine the dependency of Z-score on head biometry.

RESULTS

The study population consisted of 406 singleton pregnancies, 267 with euploid fetuses, 81 with trisomy 21, 50 with trisomy 18 and eight with trisomy 13. In the euploid group, the mean CSP width was 4.5 (range, 1.8-7.4) mm. Regression analysis showed a significant dependency of CSP width on BPD (CSP width = 0.658 + (0.064 × BPD), r = 0.781, P < 0.0001; both parameters in mm). The mean CSP width increased from 3.2 to 7.1 mm for BPD values of 40 to 100 mm, respectively. In the groups of fetuses with trisomy 21, 18 and 13, mean CSP width was 5.7 (range, 2.8-10.5), 7.9 (range, 3.5-12.8) and 5.8 (range, 4.0-9.0) mm, respectively. In 42.0% of the fetuses with trisomy 21, CSP width was above the 95(th) centile. In trisomy 18 and 13, CSP width was above the 95(th) centile in 92.0% and 37.5% of cases, respectively.

CONCLUSION

A large CSP width should prompt a detailed ultrasound examination to further assess the risk for chromosomal abnormalities.

Comparison of three first trimester screening algorithms for trisomy 21 with and without adjustment for maternal characteristics

PURPOSE

Comparison of three algorithms (DoE 2007 and DoE 2011 algorithm of the FMF Germany and MoM algorithm of the FMF UK) in first trimester biochemical screening for trisomy 21 based on maternal and gestational age, free ß-hCG, and PAPP-A and assessment of relevant maternal characteristics.

MATERIALS AND METHODS

Data from 22 449 euploid singleton pregnancies undergoing combined screening for trisomy 21 at 11 to 13 weeks of gestation were examined. The measured maternal free β-hCG and PAPP-A concentrations were converted into DoE 2007 and DoE 2011 values according to the algorithm of the FMF Germany and into MoM values according to the algorithm of the FMF UK. In each pregnancy, patient-specific risks and false-positive rates (FPR) were computed according to the three algorithms and were stratified according to gestational age, maternal ethnicity, maternal weight, and smoking status.

RESULTS

Free ß-hCG and PAPP-A MoM and DoE 2011 were acceptably independent from maternal characteristics and gestational age, while there was a strong relationship between maternal weight and the DoE 2007 values. For a risk cut-off that corresponds to an overall 5 % FPR rate for each algorithm, the FPR in each group were around 5 % at gestational week 11 - 13. The FPR of the DoE 2007 algorithm increased linearly with maternal weight from 3.6 % in women of 50 kg or less to 11.8 % in women of more than 110 kg.

CONCLUSION

Especially maternal weight has a significant impact on the risk calculation. In contrast to the DoE 2007 algorithm, the DoE 2011 and MoM algorithms both adjust for maternal weight.

Prefrontal space ratio in second- and third-trimester screening for trisomy 21

OBJECTIVE

To evaluate the prefrontal space ratio (PFSR) in second- and third-trimester euploid fetuses and fetuses with trisomy 21.

METHODS

This was a retrospective study utilizing stored mid-sagittal two-dimensional images of second- and third-trimester fetal faces that were recorded during prenatal ultrasound examinations at the Department of Prenatal Medicine at the University of Tuebingen, Germany and at a private center for prenatal medicine in Nuremberg, Germany. For the normal range, 279 euploid pregnancies between 15 and 40 weeks' gestation were included. The results were compared with 91 cases with trisomy 21 between 15 and 40 weeks. For the ratio measurement, a line was drawn between the leading edge of the mandible and the maxilla (MM line) and extended in front of the forehead. The ratio of the distance between the leading edge of the skull and the leading edge of the skin (d1) to the distance between the skin and the point where the MM line was intercepted (d2) was calculated. The PFSR was determined by dividing d2 by d1.

RESULTS

In the euploid and trisomy 21 groups, the median gestational age at the time of ultrasound examination was 21.1 (range, 15.0-40.0) and 21.4 (range, 15.0-40.3) weeks, respectively. Multiple regression analysis showed that PFSR was independent of maternal and gestational age. In the euploid group, the mean PFSR was 0.97 ± 0.29. In fetuses with trisomy 21, the mean PFSR was 0.2 ± 0.38 (P < 0.0001). The PFSR was below the 5(th) centile in 14 (5.0%) euploid fetuses and in 72 (79.1%) fetuses with trisomy 21.

CONCLUSION

The PFSR is a simple and effective marker in second- and third-trimester screening for trisomy 21.

Assessment of Foetal DNA in Maternal Blood - A Useful Tool in the Hands of Prenatal Specialists

Over the last few years, first trimester screening between 11+ and 13+ weeks of gestation has become one of the most important ultrasound examinations in pregnancy, as it allows physicians to predict several pregnancy complications including pre-eclampsia or pre-term birth. Screening for trisomies 21/18 and 13 using maternal and gestational age, foetal nuchal translucency, and maternal serum biochemistry was formerly the main reason for first trimester screening. However, today this is only one part of the overall examination. In the near future, the analysis of foetal DNA obtained from maternal blood will be used to supplement first trimester screening for aneuploidy or even replace current screening methods. In this review we show how prenatal medicine specialists can use foetal DNA analysis.

First-trimester combined screening for trisomy 21 with different combinations of placental growth factor, free β-human chorionic gonadotropin and pregnancy-associated plasma protein-A

OBJECTIVE

To examine placental growth factor (PlGF) in euploid and trisomy 21 pregnancies at 11-13 weeks' gestation and to model the impact on first-trimester combined screening.

METHODS

PlGF was measured in 509 (409 euploid and 100 trisomic) fetal serum samples derived from prospective first-trimester combined screening for trisomy 21 at 11-13 weeks' gestation. The serum samples were stored at -80°C, following the measurement of free β-human chorionic gonadotropin (β-hCG) and pregnancy-associated plasma protein-A (PAPP-A) levels, for median time spans of 0.9 and 4.1 years in the euploid and trisomy 21 pregnancies, respectively. The effect of additional PlGF measurement at the time of combined screening was investigated by simulating fetal nuchal translucency (NT) measurements and multiples of the median (MoM) values for PAPP-A, free β-hCG and PlGF for 20,000 euploid and 20,000 trisomy 21 pregnancies. Patient-specific combined risks were calculated based on maternal age and fetal NT in addition to free β-hCG, PAPP-A and PlGF, PAPP-A and PlGF or free β-hCG and PlGF, and detection and false-positive rates were calculated.

RESULTS

Median PlGF-MoM was 1.0 (95% confidence interval (CI), 0.96-1.04) in euploid fetuses and significantly lower, at 0.73 (95% CI, 0.70-0.76), in trisomy-21 fetuses (P < 0.0001). There was no significant dependency between PlGF-MoM and either gestational age at the time of blood sampling (r = 0.087, P = 0.392) or sample storage time (r = 0.028, P = 0.785). Modeled detection and false-positive rates for first-trimester combined screening (based on maternal and gestational age, fetal NT and maternal serum biochemistry) without PlGF were 85% and 2.7% for a fixed risk cut-off of 1:100. The addition of PlGF increased the detection rate to 87% and reduced the false-positive rate to 2.6%. Screening by maternal age and fetal NT in combination with PlGF and PAPP-A or in combination with PlGF and free β-hCG provided detection rates of 82% and 79%, with false-positive rates of 2.7% and 3.0%, respectively.

CONCLUSION

In pregnancies with trisomy 21 PlGF is reduced. The impact on the overall screening performance for trisomy 21 is low and does not justify the measurement of PlGF solely for trisomy 21 screening. However, as PlGF is measured with the aim of assessing the risk for pre-eclampsia, further improvement in screening for trisomy 21 can be considered as an added benefit.

Impact of bias in crown-rump length measurement at first-trimester screening for trisomy 21

OBJECTIVE

To assess the repeatability of crown-rump length (CRL) measurement and examine the effect of its over- and underestimation on first-trimester combined screening.

METHODS

Intra- and interoperator repeatability of CRL measurement at 11-13 weeks of gestation was assessed in 124 cases by two operators. Raw data were transformed into gestational age and intra- and interoperator repeatability was evaluated by within-operator standard deviation (SD) and the SD of differences in measurements between both operators. Modeling techniques were used to assess the impact of CRL measurement error on general population screening and on the operator-specific screening performance. The impact of errors in CRL measurement were investigated by simulating fetal nuchal translucency (NT) measurements and multiple of the median (MoM) values for pregnancy-associated plasma protein A (PAPP-A) and free β-human chorionic gonadotropin (β-hCG) for 500 000 euploid and 500 000 trisomy 21 pregnancies at 12 weeks and 9 weeks of gestation, and adding to or subtracting from each CRL value up to 10 mm and recalculating patient-specific risks.

RESULTS

Within-operator SD of the CRL measurement was 1.27 days of gestation. The SD of the differences in CRL measurement between operators was 1.37 days of gestation. Both intra- and interoperator 95% limits of agreement were around ± 5 mm. In general population-based screening, a CRL measurement error SD of 5 mm accounts for an estimated 5% of the SD of log MoM PAPP-A and less than 1% of the SD of log MoM free β-hCG. Modeling the effect of removing this measurement error on overall screening performance showed a minimal impact. For a risk cut-off of 1 in 100, the benefit in terms of overall screening performance would be an increase in detection rate of about 1% and a reduction in false-positive rate of less than 0.1%. With regard to the operator-specific screening performance, a consistent 5-mm underestimation of CRL reduces the detection rate from 84% to 79% and the false-positive rate from 2.4% to 1.2%. With a consistent 5-mm overestimation the rates would be 88% and 5.6%, respectively.

CONCLUSION

The impact of the interoperator variability in CRL measurement on patient-specific risk needs to be taken into account when interpreting first-trimester screening results. A systematic under- or overestimation of CRL should be avoided.

[Sonographic criteria for the differentiation of benign and malignant breast lesions using real-time spatial compound imaging in combination with XRES adaptive image processing]

PURPOSE

The purpose of the study was to analyze sonographic criteria for the differentiation of benign and malignant breast lesions using real-time spatial compound imaging (CT) in combination with adaptive image processing (XRES).

MATERIALS AND METHODS

In a retrospective analysis of 460 patients, the sonographic criteria: shape, orientation, margin, echo pattern and posterior acoustic features were determined using CT and XRES. All investigations were performed using a 12 MHz linear transducer. The findings were classified according to the DEGUM criteria analogous to BIRADS and were histologically confirmed by core needle or vacuum biopsy. Statistical analysis was performed using a Chi-square test, logistic uni- and multivariate regression analysis and an ROC-curve analysis to detect the false-positive rate.

RESULTS

All investigated diagnostic criteria were significant in the descriptive analysis (Chi-squared). The multivariate analysis showed that the criteria of irregular shape versus round, and not circumscribed margin versus circumscribed margin as well as the posterior acoustic features of enhanced versus reduced have a significant influence on the prediction of a malignant finding. The univariate analysis also showed a statistical significance using the indifferent and not parallel orientation versus parallel. To attain a detection rate of > 95 %, a false-positive rate of 60 % must be expected.

CONCLUSION

This study shows that when using CT in combination with XRES, the analyzed sonographic criteria for the differentiation of benign and malignant breast lesions are still of diagnostic value. In particular, the shape, margin and posterior sonographic features are important.

Intra- and interoperator reliability of manual and semi-automated measurements of intracranial translucency

OBJECTIVES

To assess the reproducibility of fetal intracranial translucency (IT) measurements performed manually or with SonoNT(®), a semi-automated caliper placement technique recently introduced for nuchal translucency thickness (NT) measurement.

METHODS

This was a retrospective study using 116 stored images of the head (mid-sagittal plane) from normal fetuses in dorsoposterior position at 11-13 weeks. Two experienced operators each measured the IT separately, twice manually and twice using the semi-automated software. Intraoperator and interoperator repeatability were assessed. The mean of the two manual measurements of the more experienced Operator 2 was considered as the 'gold standard'.

RESULTS

Seven cases were excluded as the IT could not be recognized by the semi-automated software. In the remaining 109 cases, the interquartile range of the mean IT measurement was 1.9-2.4 mm for Operator 1 and 1.8-2.3 mm for Operator 2 for both the manual and the semi-automated IT measurements. The intraoperator SD for manual measurements was 0.091 mm for Operator 1 and 0.088 mm for Operator 2, and for semi-automated measurements it was 0.054 mm for Operator 1 and 0.067 mm for Operator 2. Concerning interoperator bias of the manual measurements, the mean difference between Operator 1 and Operator 2 was - 0.09 (95% CI, - 0.11 to - 0.07) mm. With respect to the gold standard, the mean bias of the semi-automated measurements was 0.01 (95% CI - 0.01 to 0.03) mm for Operator 1 and - 0.09 (95% CI - 0.11 to - 0.07) mm for Operator 2, indicating good agreement.

CONCLUSIONS

Manual IT measurements are reproducible. In addition, IT can be assessed reliably using the semi-automated NT algorithm, leading to standardization of the IT assessment process.

Prospective detection of open spina bifida at 11-13 weeks by assessing intracranial translucency and posterior brain

We describe a case series of six fetuses with open spina bifida (OSB) from four different prenatal units, where the anomaly was detected at the routine 11-13-week ultrasound examination. Crown-rump length ranged from 49 to 78 mm. All cases were first suspected during nuchal translucency thickness measurement in the mid-sagittal plane of the face. OSB was lumbosacral in five fetuses and cervical in one. The intracranial translucency (IT) was obliterated in two cases, but some fluid was found in the other four cases. However, in all cases the typical landmarks of a normal posterior brain and normal IT were absent. In all six cases the ratio of brainstem diameter to brainstem-occipital bone distance was increased (≥ 1). This detection of an abnormal posterior brain led to a targeted examination and detection of the spinal lesion during the same examination in five cases, whereas in one suspicious case the patient was recalled at 17 weeks, when the abnormality was detected. Two fetuses had both multiple anomalies and trisomy 18. These prospective cases demonstrate the feasibility of using the standard mid-sagittal plane commonly used for NT measurement to assess the IT and the posterior brain and to determine the presence of OSB during NT screening.

Prenatal evaluation of the position of the fetal conus medullaris

OBJECTIVES

To determine the position of the fetal conus medullaris during pregnancy in relation to the last vertebral body and to examine its use in detecting skin-covered spinal dysraphism.

METHODS

This was a retrospective study involving 300 consecutive ultrasound examinations between 15 weeks of gestation and term. Two operators independently assessed images of the spine to determine whether the conus medullaris and the last vertebral body could be visualized in a single image in a midsagittal plane. The distance between these two landmarks (the conus distance) was measured twice by both operators who were not aware of any previous measurements. Intra- and interobserver variability was assessed by 95% limits of agreement. Linear regression analysis was used to determine the relevant contributors to the conus distance and a normal range was computed based on the best-fit model. The normal results were compared with five cases of prenatally detected skin-covered spinal dysraphism.

RESULTS

In 84.7% of the 300 cases, both operators were able to visualize the conus medullaris and the last vertebral body. Ninety-five percent limits of agreement for the intraobserver variability in measurement of conus distance were ± 1.9 mm. For the interobserver variability, they were - 3.7 and 2.5 mm. We found a linear relationship between conus distance and gestational age, biparietal diameter and abdominal circumference. The strongest relationship was observed for femur length (conus distance = - 8.2 + femur length (mm)). In the five abnormal cases, conus distance was well below the 5(th) percentile.

CONCLUSIONS

Determination of conus distance allows for an objective and feasible assessment of the conus medullaris position. This parameter promises to be useful in the prenatal detection of skin-covered spinal dysraphism.

Impact of bias in serum free beta-human chorionic gonadotropin and pregnancy-associated plasma protein-A multiples of the median levels on first-trimester screening for trisomy 21

OBJECTIVE

To examine the effect of bias in median multiples of the median (MoM) levels of pregnancy-associated plasma protein-A (PAPP-A) and free beta-human chorionic gonadotropin (β-hCG) on first-trimester combined screening for trisomy 21.

METHODS

The effects of deviations in the MoM levels of free β-hCG and PAPP-A were investigated by simulating nuchal translucency (NT) at 12 weeks and MoM values for PAPP-A and free β-hCG for 500 000 euploid and 500 000 trisomy 21 pregnancies at 9 and at 12 weeks of gestation. Likelihoods were calculated using the mixture model for NT and the standard Gaussian model for log MoM PAPP-A and free β-hCG values. Deviations in MoM marker levels were simulated by applying percentage changes of 5% to 20% to MoM values. Detection and false-positive rates were calculated with and without adjustments of the maternal serum marker levels by taking the proportion of euploid and aneuploid cases above given thresholds for each maternal age and then taking a weighted average with respect to the maternal age distribution.

RESULTS

With median MoM levels on target, the modeled detection and false-positive rates in combined screening for trisomy 21 at 12 weeks of gestation with a fixed risk cut-off of 1 in 100 were 85% and 2.5%, respectively. For median MoM levels of free β-hCG and PAPP-A between 0.8 and 1.2 MoM, detection rates ranged from 77% to 91%, with corresponding false-positive rates ranging from 1.0% to 6.1%.

CONCLUSION

In first-trimester screening for trisomy 21, biases in the serum marker MoM levels of 10% can increase false-positive rates by over 50%, whilst biases of 20% can more than double false-positive rates.

[Cross-validation of the first trimester screening algorithm of the FMF London on 38,700 pregnancies in Germany]

PURPOSE

Validation of the performance of the new algorithm of the FMF London for screening for trisomy 21 using a combination of maternal age, fetal nuchal translucency (NT) and maternal serum free β-hCG and PAPP-A.

MATERIALS AND METHODS

Between 2002 and 2007, NT was measured prospectively in 39,004 pregnancies in the context of routinely performed first trimester screening in Germany. Individual trisomy 21 risks were calculated by a combination of NT, maternal age, free β-hCG, and PAPP-A using the FMF algorithm in force at the time of investigation. In this study we recalculated the trisomy 21 risks applying the new algorithm of the FMF UK that includes the new mixture model for the NT measurement.

RESULTS

38,751 singleton pregnancies could be included in the study of which 109 (0.3 %) had a trisomy 21. Only 35 % of the NT measurements of euploids were above the median and 25 % of the NT measurements were below the 5th percentile of the FMF UK. For sonographers that were qualified according to level II or III of the German DEGUM system, the median NT of fetuses with trisomy 21 was 0.9 mm above the median of the FMF UK and only 0.5 mm above the median for all other sonographers. Despite the limited performance of the NT measurement, the overall detection rate for a trisomy 21 was 90.8 % when combining the NT with maternal age, PAPP-A and free β-hCG. The overall false-positive rate for a trisomy 21 was 6.5 % at a cut-off value of 1:300.

CONCLUSION

In this study we were able to show that the use of the new risk algorithm of the FMF UK leads to a trisomy 21 detection rate of about 90 % at a 5 % false-positive rate in a German collective despite a significant underestimation of the NT.

Impact of the maternal age-related risk in first-trimester combined screening for trisomy 21

OBJECTIVE

To examine the impact of the maternal age-related risk in first-trimester combined screening for trisomy 21.

METHODS

Prospective assessment of risk for trisomy 21 by a combination of maternal age, fetal NT thickness and maternal serum PAPP-A and free β-hCG at 11+0 to 13+6 weeks of gestation between April 2002 and February 2007. Screening for trisomy 21 by patient-specific risks based on the maternal and gestational age-related risk multiplied by a likelihood ratio for NT and for maternal serum biochemistry were compared with a screening policy that is only based on the combined likelihood ratio for fetal NT and maternal serum biochemistry.

RESULTS

The study population consisted of 38,603 euploid pregnancies and 109 fetuses with trisomy 21. In screening for trisomy 21 by fetal NT and maternal serum biochemistry in combination with and without maternal age with a fixed false-positive rate of 3%, the detection rate was 82.6 and 79.8%, respectively. In the group of women with a maternal age of less than 30 years and between 30 and 35 years, there was no difference in the detection rate. For women with a maternal age of 35 years or older, the detection rate increased from 77.1% without maternal age to 94.3% with maternal age, respectively.

CONCLUSION

The overall difference between first-trimester screening based on fetal NT and maternal serum biochemistry with and without maternal age is about 3%. In screening with a fixed cut-off, the maternal age-related risk keeps the false-positive rate low in younger women and increases the detection rate in older women.

Assessment of the ductus venosus, tricuspid blood flow and the nasal bone in second-trimester screening for trisomy 21

OBJECTIVE

To examine the prevalence of reversed a-wave in the ductus venosus, tricuspid regurgitation and absent nasal bone, in a second-trimester population undergoing amniocentesis, after exclusion of major fetal defects and to estimate the performance in screening for trisomy 21 based on maternal age and these markers in a general population.

METHODS

This was a retrospective study involving pregnancies undergoing amniocentesis due to increased risk for trisomy 21, mainly because of advanced maternal age. Before the invasive procedure, an ultrasound examination was carried out to exclude major fetal defects and to examine the ductus venosus, tricuspid blood flow and the presence of the fetal nasal bone. Modeling techniques were used based on 20 000 euploid pregnancies and 20 000 pregnancies with trisomy 21 to assess the screening performance in a general population.

RESULTS

The study population consisted of 3613 euploid pregnancies and 35 cases with trisomy 21. In the euploid group, reversed flow in the ductus venosus, tricuspid regurgitation and an absent nasal bone was observed in 1.7%, 1.5% and 0.1% of cases, respectively. In the trisomic group, these markers were found in 14.3%, 11.4% and 14.3% of cases, respectively. For a 5% false-positive rate, the detection rate in screening for trisomy 21, based on maternal age and either ductus venosus, tricuspid blood flow or nasal bone would be 33.8%, 32.4% or 31.4%, respectively. Screening by maternal age alone would detect 29.0% of the fetuses with trisomy 21. Receiver-operating characteristics curve analysis showed a slight but significant improvement in screening performance for trisomy 21 based on the inclusion of these markers.

CONCLUSION

Second-trimester ultrasound screening for trisomy 21 based on maternal age with additional assessment of the ductus venosus, tricuspid blood flow and the fetal nasal bone in otherwise normal-appearing fetuses is only marginally better than is screening by maternal age alone.

Two-stage first-trimester screening for trisomy 21 by ultrasound assessment and biochemical testing

OBJECTIVES

This study was carried out to examine the performance of a contingent policy in first-trimester screening for trisomy 21, in which the estimated risk was first derived by a combination of maternal age, fetal nuchal translucency (NT) thickness, presence/absence of the nasal bone, blood flow in the ductus venosus or flow across the tricuspid valve, and biochemical testing was carried out only in those who were found to have an intermediate risk. We also examined the performance of a policy in which the estimated risk was first derived by a combination of maternal age and biochemical testing, and ultrasound examination was carried out only in those with an intermediate risk.

METHODS

The data for this study were derived from prospective screening for trisomy 21 in singleton pregnancies, using, as markers, a combination of maternal age, fetal NT thickness and maternal-serum free β-human chorionic gonadotropin (β-hCG) and pregnancy-associated plasma protein-A (PAPP-A), in a one-stop clinic for first-trimester assessment of risk at 11 + 0 to 13 + 6 weeks of gestation. Assessment of the fetal nasal bone, ductus venosus flow and tricuspid flow were also routinely performed by appropriately trained sonographers. The performance of different screening policies was examined.

RESULTS

The study population consisted of 19 614 pregnancies with a normal karyotype or delivery of a phenotypically normal baby (euploid group) and 122 cases of trisomy 21. The best performance was achieved by a contingent policy in which first-stage screening was based on maternal age, fetal NT thickness and either tricuspid valve or ductus venosus blood flow, followed by biochemical testing only those with an intermediate risk, of 1 in 51 to 1 in 1000 (which constituted about 20% of the total). The performance of contingent screening in which first-stage testing relies on biochemistry was poorer than when first-stage screening was performed by ultrasound examination because, in order to achieve the same detection rate, the false-positive rate was twice as high.

CONCLUSION

Effective first-trimester screening for trisomy 21 can be achieved by a contingent policy in which first-stage testing is based on ultrasound examination and second-stage biochemical testing is carried out in only 20% of the patients.

Intra- and interoperator reliability of manual and semi-automated measurement of fetal nuchal translucency by sonographers with different levels of experience

OBJECTIVE

To compare the intra- and interoperator reliability of manual and semi-automated nuchal translucency thickness (NT) measurement by sonographers with different levels of experience.

METHODS

From our digital database we selected retrospectively 70 NT images without measurements and of highest quality according to the guidelines of The Fetal Medicine Foundation (FMF). Four operators (two experts who were consultants in fetal medicine, one general consultant in obstetrics and gynecology with average knowledge in obstetric ultrasound and one final-year medical student with no experience in ultrasound), having first attended the FMF's online NT measurement course, measured the fetal NT manually according to FMF guidelines and semi-automatically from the inner to inner borders of the two echogenic lines delineating the NT and from the inner border to the middle of the lower NT line. The semi-automatic measurement algorithm identifies the two NT lines within a manually chosen region of interest and standardizes the caliper placement process. Each operator was blinded to any pre-existing measurements. Each measurement was performed twice by each operator. Intraoperator repeatability was assessed by the within-operator SD and intraclass correlation coefficients (ICC). Interoperator reliability was assessed by comparison with the mean manual measurement of the experts, which was considered as the gold standard.

RESULTS

The mean NT measurement of the four sonographers was between 1.9 and 2.0 mm with both the manual and the semi-automated inner-inner NT measurement and it was between 2.2 and 2.3 mm with the semi-automated inner-middle method. The within-operator SDs of the manual measurement for both experts were similar and significantly lower than those of the non-experts, and all four sonographers performed similarly with the semi-automated measurement. Concerning the interoperator biases relative to the manual measurements of the experts taken as the gold standard, the manual measurements of the student and the general consultant were significantly lower, by 0.18 mm and 0.12 mm. The semi-automated inner-inner measurements of all four sonographers were much closer to the gold standard, although there was still a significant underestimation (mean differences from gold standard between 0.04 and 0.06 mm). With the semi-automated inner-middle measurement there was a significant and more pronounced overestimation of fetal NT compared with the gold standard, relative biases ranging from 0.08 to 0.23 mm above it.

CONCLUSION

Semi-automation of NT measurement leads to improved standardization of the NT assessment process. In particular, non-expert operators improve as the variability in their caliper placement can be reduced to the level of experts. However, the most important contributor to the inter- and intraoperator variability of NT assessment is that of image acquisition, which is not affected by semi-automation of NT measurement.

The 11-13-week scan: diagnosis and outcome of holoprosencephaly, exomphalos and megacystis

OBJECTIVE

To determine the prevalence and outcome of fetuses with holoprosencephaly, exomphalos and megacystis diagnosed at 11-13 weeks of gestation.

METHODS

As part of a prospective screening study for trisomy 21 in singleton pregnancies at 11 + 0 to 13 + 6 weeks' gestation, transabdominal ultrasound examination was performed to diagnose holoprosencephaly, exomphalos and megacystis. Fetal karyotype and pregnancy outcome in fetuses with these defects were examined.

RESULTS

Screening was carried out in 57 119 pregnancies. The prevalence of holoprosencephaly, exomphalos and megacystis was 1 : 1298, 1 : 381 and 1 : 1632, respectively. Chromosomal abnormalities, mainly trisomies 18 and 13, were found in 65.9% of fetuses with holoprosencephaly, in 55.3% with exomphalos and in 31.4% with megacystis. There was spontaneous resolution of the defect by 20 weeks in 92.5% of euploid fetuses with exomphalos containing only bowel and in 90% of the euploid fetuses with megacystis and bladder length of < or = 15 mm.

CONCLUSIONS

A high proportion of fetuses with holoprosencephaly, exomphalos and megacystis diagnosed at 11-13 weeks of gestation are aneuploid, but in the majority of cases exomphalos and megacystis represent temporary abnormalities that resolve spontaneously.