Affiliations 1 Centre for ultrasound and prenatal medicine, Frankfurt/ Main, Germany 2 amedes MVZ für Laboratoriumsmedizin, Göttingen, Germany 3 Amedes experts Barkhof, Germany 4 Institut für Laboratoriumsmedizin und Klinische Genetik, Essen, Germany 5 Centre for prenatal medicine, Leipzig, Germany 6 Ultraschall Freie Strasse Basel, Switzerland 7 FMF Audit Centre Germany, Adelebsen, Germany 8 Department of Medical Biostatistics, Epidemiology and Informatics of the University of Mainz, Mainz, Germany 9 Department of Biostatistics, CIMH Mannheim, Mannheim Medical School of the University of Heidelberg, Mannheim, Germany published online 2022

Aim: Both previous versions of the German PRC algorithm developed by our group for routine first-trimester screening relied on the assumption that maternal blood sampling and fetal ultrasonography are performed at the same visit of a pregnant women. In this paper we present an extension of our method allowing also for constellations where this synchronization is abandoned through preponing blood sampling to dates before 11 weeks of gestation.Methods: In contrast to the directly measured concentrations of the serum parameters PAPP-A and free B-hCG, the logarithmically transformed values could be shown to admit the construction of reference bands covering the whole range from 16 to 84 mm CRL [corresponding to 63 to 98 days of gestation]. Prior to determining reference limits from which the DoEs for each individual patient had to be calculated, the log concentrations of all PAPP-A and free B-hCG values were transformed once more using the calibration approach established in [1] for the elimination of the influence of maternal weight.Results: Although that part of the database which was available for estimating the reference bands for blood sampling times prior to 11 weeks of gestation was comparatively sparse (898 out of 186 215 pregnancies with euploid outcome), the key statistical characteristics of the extended risk-calculation procedure turned out to be very satisfactory. Using the same cutoff value of 1: 150 for the posterior risks of trisomy 21 and 13/18, the overall FPR (false positive rate) for diagnosing a T21 was found to be 3.42 %. The corresponding DTR (detection rate) was obtained to be 86.8 % and thus exceeded the DTR attained by PRC 2.0 for trisomy 21. For trisomies 13 and 18, the proportions of patients with calculated posterior risks exceeding the cutoff value of 1: 150 were obtained to be 1.60 % (= FPR) and 86.4 % (= DTR).Conclusion: Transforming the measured concentrations of PAPP-A and free B-hCG to the logarithmic scale allows one to extend the DoE-based algorithm developed by the FMF Germany for diagnosing trisomies 21 and 13/18 in such a way that it can be applied to constellations where blood sampling is done before 11 weeks of gestation.

OP07.05 Detection of chromosome abnormalities in twin gestations at 11+2 to 14+0 weeks S. Roepstorff1, L. Engelbrechtsen1, C. K. Ekelund2, A. Tabor2,3, L. Skibsted1,3 1Department of Gynecology and Obstetrics, Roskilde University Hospital, Roskilde, Denmark; 2Department of Fetal Medicine, Copenhagen University Hospital, Rigshospitalet, Copenhagen, Denmark; 3Faculty of Health Sciences, University of Copenhagen, Copenhagen, Denmark

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 beta-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 beta-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 beta-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.

AIMIn the algorithm developed by the Fetal Medicine Foundation (FMF) Germany designed to evaluate the findings of routine first-trimester screening, the false-positive rate (FPR) was determined for the entire study group without stratification by maternal weight. Based on the data received from the continuous audit we were able to identify an increase in the FPR for the weight-related subgroups of patients, particularly for patients with extremely high body weights. The aim of this study was to demonstrate that the variability of the FPR can be reduced through adjusting the concentrations of free β-HCG and PAPP-A measured in the maternal serum by means of a nonlinear regression function modeling the dependence of these values on maternal weight.MATERIAL AND METHODSThe database used to establish a version of the algorithm enabling control of the FPR over the whole range of maternal weight consisted of n = 123 546 pregnancies resulting in the birth of a child without chromosomal anomalies. The group with positive outcomes covered n = 500 cases of trisomy 21 and n = 159 trisomies 13 or 18. The dependency of the serum parameters free β-HCG and PAPP-A on maternal weight was analyzed in the sample of negative outcomes by means of nonlinear regression. The fitted regression curve was of exponential form with negative slope. Using this model, all individual measurements were corrected through multiplication with a factor obtained as the ratio of the concentration level predicted by the model to belong to the average maternal body weight of 68.2 kg, over the ordinate of that point on the regression curve which belongs to the weight actually measured. Subsequently, the totality of all values of free β-HCG and PAPP-A corrected for deviation from average weight were used as input data for carrying out the construction of diagnostic discrimination rules described in our recent paper for a database to which no corrections for over- or under-weight had been applied. This entailed in particular the construction of new reference bands for the corrected biochemical values as the basis for calculating the degree of extremeness (DOE) measures to replace the more traditional MOMs. In the final and most crucial step, stratified FPRs were computed and compared over a set of intervals partitioning the whole range of maternal weight into 18 classes.RESULTSFor the posterior risks of both trisomy 21 and 13 / 18 computed from the weight-corrected database, the use of a cutoff value of 1:150 turned out to be an appropriate choice. For T 21, the overall FPR obtained through comparing the individual risks with this cutoff was found to be 3.51 %. The corresponding proportion of ascertained cases of trisomy 21 detected by means of the new algorithm was 86.2 %. For the trisomy 13 / 18 group, the analogous results were a FPR of 2.07 % and a detection rate (DTR) of 83.0 %, respectively. A comparison between the FPRs obtained for the 18 intervals into which the range of maternal weight had been partitioned, showed the deviation of the strata-specific from the overall FPR to be fairly small: for T 21, the FPR ranged from 2.72 to 4.86 %, and the maximum was found in the group of 87.5 - 95.0 kg. For women with a weight of more than 120 kg, the FPR was only slightly above the FPR for the total sample (3.69 as compared to 3.51 %). Similar results were obtained for the discrimination rule constructed for diagnosing T 13 / 18: here, the minimum FPR (1.17 %) was found for patients weighing more than 120 kg, whereas the maximum (2.66 %) occurred in the interval 75.0 - 77.5 kg.CONCLUSIONIn this study we demonstrated that the new algorithm developed by the FMF Germany to estimate risks for fetal trisomies 21 and 13 / 18 combines very good misclassification rates with a far-reaching stability of the false-positive rate against even extreme deviations from the average maternal weight.

The aim of this study was to determine if weight corrected values of free beta-HCG and PAPP-A do in fact exert an influence on the detection rate of trisomy 21 in first-trimester screening, using the algorithm of FMF-Germany without weight correction and the algorithm of FMF-UK with weight correction. Standard parameters in both systems were maternal age, CRL, nuchal translucency thickness (NT) and maternal serum free beta-hCG and PAPP-A. In 71.773 pregnant Caucasian women the risk for a chromosomal defect was calculated with the German program PRC (prenatal risk calculation) and the FMF-UK program. Trisomy 21 was detected in 254 out of the 71.773 cases. All trisomy 21 cases were divided into three groups based on the maternal weight: group A: maternal weight ⩽ 70.00 kg, group B: 70.01–100.00 kg and group C: > 100.00 kg. With consideration of a false positive rate of 5.0%, the detection rates of trisomy 21 calculated using the German and the British algorithm were 83.2% with the German program, and 82.9% with the British program. Comparing the results in the 3 different weight groups there was no significant difference in the detection rate of trisomy 21, neither in the low weight group nor in the high weight group. The findings of the present study calculated on the basis of both the German and the British program do not show a higher detection rate of trisomy 21 when using weight corrected values of free beta-HCG and PAPP-A.

K. Dlouha1, I. Kucerova1, P. Calda2, D. Smetanova3, M. Brestak4, A. Hudec5, H. Viskova2, D. Stejskal3, J. Turek5, I. M. Malbohan6 1Institute for the Care of the Mother and Child, Prague, Czech Republic, 2Department of Obstetrics and Gynecology, First Medical Faculty, Charles University, Prague, Czech Republic, 3Gennet, Centre for Genetics and Assisted Reproduction, Prague, Czech Republic, 4Pronatal, Centre for Assisted Reproduction, Prague, Czech Republic, 5Department of Obstetrics and Gynecology, Medical Faculty in Pilsen, Charles University, Pilsen, Czech Republic, 6Department of Medical Biochemistry, First Medical Faculty, Charles University, Prague, Czech Republic

Purpose: First-trimester screening at 11 - 14 weeks has been proven to be very useful in the early detection of chromosomal defects. The aim of this project was to develop a CE-certified new risk calculation program (PRC = Prenatal Risk Calculation) using a nationwide database.Materials and Methods: The database underlying the new risk calculation procedure was established in Germany from 2003 through 2006. Overall, the database includes measurements from 70,030 pregnant women having given birth to healthy children. Following consideration of all pregnancies associated with a chromosomally abnormal outcome, the sample size was 451. The algorithm used for calculating the risk of a chromosomally abnormal outcome comprises the following variables: maternal age, crown-rump length (CRL) (restricted to a range from 45 -84mm or, equivalently, 11 +1 - 14+0 weeks of gestation), nuchal translucency (NT), as well as the maternal serum parameters PAPP-A (pregnancy associated plasma protein A) and free beta-hCG (free human chorionic gonadotropin). In a preliminary cross-validation study, we applied both the new algorithm and the FMF UK program to an independent sample containing n = 40,568 pregnancies with negative outcome, n = 187 cases of trisomy 21, n = 34 trisomies 18 and n = 13 trisomies 13.Results: Using the primary sample of 70,030 pregnancies with a negative outcome, reference bands were constructed for the sonographic parameter fetal nuchal translucency and the biochemical parameters PAPP-A and free beta-HCG. Instead of MoM values we used "degree of extremeness" (DoE) values. This statistical parameter has been proven to give more precise results than the MoM Measure because it assesses the deviation of the actual measurement value from the centre of the reference band expressed as a multiple of the width of the respective band section. The result of the risk calculation is visualized by means of a traffic light graph which allows the patient to comprehend her individual risk at first glance. The red color indicates a high risk, green a low risk, and yellow represents a moderate risk. In our preliminary cross-validation study the detection rate obtained for the German algorithm was 86.6% for trisomy 21, 94.1% for trisomy 18 and 92.4 for trisomy 13. The corresponding detection rates obtained with the same data by the FMF UK program were 86.1%, 82.3% and 69.2% throughout. The false-positive rate was 5.0% throughout.Conclusion: The new risk calculation procedure of the FMF Germany (PRC) has been made available as a CE-certified computer program. In screening for trisomy 21 it yields results comparable to those of the program used by the FMF UK. Regarding the diagnosis of trisomy 13 and 18, even higher detection rates are currently achieved with the German algorithm. Program, data base and license key are available free of charge to registered members of the FMF Germany.

Seit dem 1. Februar 2007 steht neben dem Risikokalkulationsprogramm der FMF England (1) das von der FMF-Deutschland (2) entwickelte Computerprogramm PRC (=Prenatal Risk Calculation) als Alternativmethode zur pränatalen Risikoabschätzung von Chromosomenstörungen zur Verfügung. Das deutsche Risikokalkulationsprogramm wurde anhand von 70030 Schwangerschaften mit gesunden Kindern und 451 Schwangerschaften mit chromosomal kranken Kindern entwickelt. Berücksichtigt werden bei der Risikokalkulation das mütterliche Alter, die Scheitel-Steiß-Länge von 54–85mm, die Nackentransparenz, und die mütterlichen Serumparameter PAPP-A und freies ß-hCG. Vom englischen System unterscheidet sich das deutsche Risikokalkulationsprogramm in verschiedenen Punkten: 1. Algorithmus, 2. graphische Darstellung (Ampelgraphik) 3. DOE- (Degree of Extremeness) anstelle von MOM-Werten, 4. Cut-off-Werte und 5. CE-Zertifikat. Vergleicht man beide Programme, so ist evident, dass aufgrund der unterschiedlichen Programmansätze (unterschiedliche Gewichtung von Ultraschall- und biochemischen Befunden, differierender statistischer Ansatz) unterschiedliche Ergebnisse resultieren müssen. Dabei ist für die Aufklärung der Patientinnen wichtig, dass die Cut-off-Level beider Systeme nicht miteinander vergleichbar sind. Eine prospektive Überprüfung beider Systeme an 40568 Schwangeren ergab, dass bei einer Falsch-positiv-Rate von 5% die Entdeckungsrate für Trisomie 21-Fälle mit beiden Systemen ähnlich hoch war (86,6% im deutschen System versus 86,1% im englischen System). Unterschiede ergaben sich hingegen in der Trisomie 13/18-Grupppe, bei der die Entdeckungsrate mit dem deutschen System bei 93,6% und mit dem englischen System bei 78,7% lag.

First-trimester combined screening (maternal age, fetal NT, maternal serum free β-hCG and PAPP-A) at 11–14 weeks of gestation has proven to be very useful in the early detection of chromosomal defects. Up to now most of the risk calculations have been carried out with a computer program provided by FMF UK. FMF Germany, a registered charity, released a new risk calculation program (named Prenatal Risk Calculation (PRC)) on 15 February, 2007. Data on 70 030 normal Caucasian women with normal fetal outcome were analyzed. Based on these data, CRL-dependent reference centiles were constructed for NT, free β-hCG and PAPP-A by means of the Wellek & Merz (1995) method. In all three cases, the band width of the lower and upper reference curve was controlled separately, ensuring that the proportion of women with normal outcome outside the reference band in either direction corresponded exactly to 5%. For the evaluation of chromosomal defects, 312 cases with trisomy 21 and 139 cases with trisomy 13/18 were taken into account. As an appropriate measure how far outside the normal range of each woman/fetus with respect to each parameter is, we used the deviation of the actual measurement value from the center of the reference band expressed as multiples of the width of the respective section of the band (= ‘degree of extreme-ness (DOE)’). At the present stage of the data acquisition procedure, the detection rates provided by the new algorithm developed by FMF Germany are 85.25% for trisomy 21 and 83.5% for trisomy 13/18. Both values correspond to a false positive rate of 5.0%. For both categories of trisomies, our approach thus compares remarkably well with data from the literature on the diagnostic accuracy of first-trimester screening for trisomies. The new risk calculation program of FMF Germany (PRC) is based on a CE-certified algorithm and yields results that are comparable to those of the program used by FMF UK.

In den vergangenen 5 Jahren wurden von unserer Laborgruppe mehr als 40.000 Ersttrimesteruntersuchungen durchgeführt. Diese wurden nach den Richtlinien der Fetal Medicine Foundation Deutschland vorgenommen. Aufgrund der Bedeutung der fetalen Nackentransparenz für die Risikobewertung wurden die sonografischen Untersuchungen ausschließlich von FMF-zertifizierte Gynäkologen/ innen vorgenommen. Die biochemischen Bestimmungen erfolgten über das FMF zertifizierte Analyensystem Krytor und die abschließende Risikobewertung über die Astraia Ersttrimestersoftware. Alle Ergebnisse mit einem Gesamtrisiko von größer 1: 300 wurden als auffällig betrachtet. Unter alle durchgeführten Untersuchungen befanden sich 201 Fälle mit Chromosomenveränderungen. 128 Fälle hiervon wiesen eine Trisomie 21 auf. Die Gesamtdetektionsrate betrug 88,9%. In 41 Fällen wurde das erhöhte Risiko ausschließlich über Veränderungen bei den biochemischen Parametern erkannt. Diese Größenordung zeigen die Bedeutung der PAPP-A und free ß-hCG Bestimmung für die Entdeckungsrate bei Aneuploidien. Neben den Morbus Down Fällen wurden 98 Trisomien 13, 18, Triploidien, Monosomien und anderen Aberrationen analysiert. Durch das Ersttrimesterscreening konnten hierbei 92% der Fälle in eine Gruppe mit erhöhtem Risikoprofil eingeordnet werden. Die hier vorgestellten Untersuchungen belegen deutlich, dass auch bei dezentral organisierten medizinischen Strukturen, wie sie in Deutschland etabliert sind, ein hoher Qualitätsstandard im pränatalen Screening durch eine konsequente Qualitätssicherung mittels Fortbildungen und kontinuierliche Auditierung erreicht werden kann. Mit dieser Studie konnten wir die hohe Wertigkeit des Ersttrimesterscreening nach den Vorgaben der FMF-Deutschland aufzeigen.