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INTRODUCTION: We aim to determine the fetal nasal bone length (NBL) percentile values that can be used in the prediction of the fetal anomaly at 11-14 weeks of gestation in a low-risk population. METHODS: Our prospective and cross-sectional study included four hundred and eighty-six singleton pregnancies who applied for the first-trimester aneuploidy screening test at 11-14 weeks of gestation. We excluded pregnant women with fetal structural or chromosomal anomaly, nuchal translucency >3mm, an absent nasal bone, and in utero fetal death. Reference and percentile values of the NBL were calculated separately for 11,12,13,and 14. gestational weeks. RESULTS: Standard NBL measurements were performed in 486 pregnancies according to inclusion and exclusion criteria. Median NBL values were computed for each gestational age (GA), for 11,12,13 and 14. weeks of gestation was found 1.6mm (range=1.1-2.5), 1.8mm (range=1.1-3.0), 2.0mm (range=1.4-3.1), and 2.2mm (range=1.7-2.8), respectively. A positive significant correlation was found between NBL and the crown-rump length (CRL) (NBL (mm) = [0.02xCRL(mm)] + 0.73, r=.483; p

Objective: To evaluate second trimester fetal nasal length measurement results in healthy singleton pregnancies in Turkey. Material and Methods: We analyzed the nasal bone lengths within 19-24 weeks in 661 pregnancies in our hospital. All pregnant women with a single healthy fetus who applied to our perinatology outpatient clinic for detailed obstetric ultrasonography were included in the study. All measurements were performed by the same clinician during routine mid-trimester ultrasound scan. Only the patients who were considered healthy by the examining pediatrician were included in the study. The parents of all fetuses are of Turkish ethnicity. Pearson correlation, regression analysis and P value were calculated between gestational week and nasal bone length. Results: Mean nasal length measurement was 6,21 ± 0,08; 6,66 ± 0,05; 6,88 ±0,05; 7,13 ± 0,08; 7,77 ± 0,11 and 8,33 ± 0,25 mm from 19 to 24 week of pregnancy, respectively. A significant positive correlation was observed between gestational week and nasal bone length. Normal values of nasal bone length measuremens are identified for each gestational weeks acoording to our data and previous 5 studies. Conclusion: In this study, we presented the data of our own center and the results obtained from other studies conducted in our country show significant differences. We are of the opinion that studies conducted by different researchers in different regions remain insufficient to reflect the nomogram of Turkish ethnic origin. For this purpose, multicenter studies are needed to cover the whole society. [ABSTRACT FROM AUTHOR]

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Abstract Background To establish the reference ranges and evaluate the efficacy of the fetal facial sonomarkers prenasal thickness (PT), nasal bone length (NBL), PT/NBL ratio and NBL/PT ratio for Down syndrome screening in the second trimester of high-risk pregnancies using two-dimensional (2D) ultrasound. Methods A prospective study was done in Thai pregnant women at high risk for structural and chromosomal abnormalities between May 2018 and May 2019. The main exclusion criteria were any fetal anatomical anomaly detected on ultrasonography or postpartum examination, abnormal chromosome or syndrome other than Down syndrome. Ultrasounds were performed in 375 pregnant women at 14 to 22 weeks’ gestation and the fetal facial parameters were analyzed. Down syndrome results were confirmed by karyotyping. The reference ranges of these facial ultrasound markers were constructed based on the data of our population. The Down syndrome screening performance using these facial ultrasound markers was evaluated. Results In total, 340 euploid fetuses and 11 fetuses with Down syndrome met the inclusion criteria. The PT, NBL, and PT/NBL ratios in the euploid fetuses gradually increased with gestation progression while the NBL/PT ratio gradually decreased between 14–22 weeks’ gestation. The NBL, PT/NBL ratio, and NBL/PT ratio all had 100% sensitivity and PT had 91% sensitivity. These facial markers had 100% negative predictive value for Down syndrome screening in the second trimester. The Bland–Altman analysis showed the intra- and inter-observer variations of PT and NBL had high intraclass correlation coefficients (ICC) in both operators, with ICCs of 0.98 and 0.99 and inter-observer ICCs of 0.99 for both operators. Conclusion The facial ultrasound markers are very useful for second trimester Down syndrome screening in our population. These facial ultrasound markers were easily identifiable and highly consistent either intra- or inter-operator by using widely-available 2D ultrasound. However, the reference ranges for these markers need to be constructed based on individual populations. Trial registration Registration number: REC 61–029-12–3. Date of registration: 18 May 2018.

Objective: The aim of this study was to determine the reference ranges of second trimester nasal bone length (NBL), pre-nasal thickness (PT), and PT/NBL ratios of lowrisk pregnant women in Turkish population. Material and Methods: Pregnant women of 16-28th gestational age who underwent ultrasonographic fetal screening between November 2021 and June 2022 were retrospectively analyzed. Fetuses with congenital malformations, high risk in antenatal screening tests, diagnosed with aneuploidy, and pregnant women of non-Turkish ethnic origin were excluded from the study. Fetuses were classified as =19+6 weeks, 20+0-20+6 weeks, 21+0-21+6 weeks, 22+0-22+6 weeks, 23+0-23+6 weeks, and =24+0 weeks. NBL, PT, and PT/NBL ratio was evaluated for each gestational age separately. Results: A total of 242 fetuses were included in the study. The mean NBL and mean PT increased with gestational age (6.42±0.65 at 20+0-20+6 weeks versus 7.65±0.79 at 23+0-23+6 weeks and 3.10±0.62 at 20+0-20+6 weeks vs. 3.55±0.63 at 23+0-23+6 weeks, respectively). Both NBL and PT were positively correlated with gestational age whereas the PT/NBL ratio was constant throughout the second trimester (PCC=0.81, p<0.001, PCC=0.56, p<0.001, and PCC=-0.07, p=0.255, respectively). The mean PT/NBL ratio in the second trimester was calculated as 0.46 (95% CI, 0.45-0.47, 5th p=0.35 and 95th p=0.62). Conclusion: The reference ranges for NBL, PT, and PT/NBL ratio may vary in different populations. Therefore, the use of population-specific nomograms may lead to higher success rates in Down syndrome screening. [ABSTRACT FROM AUTHOR]

Background: To establish the reference ranges and evaluate the efficacy of the fetal facial sonomarkers prenasal thickness (PT), nasal bone length (NBL), PT/NBL ratio and NBL/PT ratio for Down syndrome screening in the second trimester of high-risk pregnancies using two-dimensional (2D) ultrasound.Methods: A prospective study was done in Thai pregnant women at high risk for structural and chromosomal abnormalities between May 2018 and May 2019. The main exclusion criteria were any fetal anatomical anomaly detected on ultrasonography or postpartum examination, abnormal chromosome or syndrome other than Down syndrome. Ultrasounds were performed in 375 pregnant women at 14 to 22 weeks' gestation and the fetal facial parameters were analyzed. Down syndrome results were confirmed by karyotyping. The reference ranges of these facial ultrasound markers were constructed based on the data of our population. The Down syndrome screening performance using these facial ultrasound markers was evaluated.Results: In total, 340 euploid fetuses and 11 fetuses with Down syndrome met the inclusion criteria. The PT, NBL, and PT/NBL ratios in the euploid fetuses gradually increased with gestation progression while the NBL/PT ratio gradually decreased between 14-22 weeks' gestation. The NBL, PT/NBL ratio, and NBL/PT ratio all had 100% sensitivity and PT had 91% sensitivity. These facial markers had 100% negative predictive value for Down syndrome screening in the second trimester. The Bland-Altman analysis showed the intra- and inter-observer variations of PT and NBL had high intraclass correlation coefficients (ICC) in both operators, with ICCs of 0.98 and 0.99 and inter-observer ICCs of 0.99 for both operators.Conclusion: The facial ultrasound markers are very useful for second trimester Down syndrome screening in our population. These facial ultrasound markers were easily identifiable and highly consistent either intra- or inter-operator by using widely-available 2D ultrasound. However, the reference ranges for these markers need to be constructed based on individual populations.Trial Registration: Registration number: REC 61-029-12-3. Date of registration: 18 May 2018. [ABSTRACT FROM AUTHOR]

Purpose: To perform a multicenter prospective study of ultrasound prenasal thickness (PT), and nasal bone length (NBL) measurement at 11-14 weeks' gestation.Methods: Ultrasound PT and NBL determination was performed in 504 normal fetuses and 17 fetuses with Down's syndrome (DS). Measurements were made from mid-sagittal 2D images acquired using a standardized technique during nuchal translucency (NT) examination. PT and NBL values were expressed in multiples of the gestation-specific normal median (MoM) and as the PT/NBL ratio. Information on PT and NBL MoMs was also combined using logistic regression. Results were classified as positive according to whether they were greater than the normal 95th centile for PT, PT/NBL and the DS risk from logistic regression equation or below the 5th centile for NBL.Results: The median value in DS cases and unaffected controls were: PT 1.26 and 0.996 MoM; and NBL 0.596 and 0.993 MoM. The proportion of DS fetuses with positive results was 41% for PT, 65% for NBL, and 82% for both the PT/NBL ratio and DS risk from the logistic regression equation. PT/NBL levels did not vary according to gestational age.Conclusion: The PT/NBL ratio is a valuable first trimester DS screening marker that can be easily determined concomitant with the NT measurement. [ABSTRACT FROM AUTHOR]

Objectives: To evaluate trends of nasal bone length (NBL), prenasal thickness (PT), nuchal fold (NF), prenasal thickness to nasal bone length (PT-NBL) ratio, and prefrontal space ratio (PFSR), measured serially in second- and third-trimester Down syndrome (DS) fetuses. Methods: Prenatal databases were searched for cases of continuing DS pregnancies with serial measurements, taken at least two weeks apart. Trends were plotted on previously reported normal ranges. Results: Serial measurements were available in 25 Down syndrome fetuses. Median gestational age (GA) was 25 weeks; average number of visits per case was 2.44, with a median interval of 39 days between investigations. In DS fetuses, NBL and PT showed fairly stable trends with gestation. PFSR, but especially NF, had a more unpredictable trend. The PT-NBL ratio was the most stable marker, remaining unchanged in 95% of cases. NBL, PT, and NF showed more deviance from the normal range with advancing gestation, but MoM values remained stable. All but two fetuses had ultrasound markers or structural anomalies, especially heart defects. Conclusions: The PT-NBL ratio is the most constant DS marker throughout gestation, following a predictable trend. © 2015 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

Objective To assess the value of the prenasal thickness to nasal bone length ratio (PT/NBL) for detecting trisomy 21 (T21) after the first trimester. Method Two examiners blinded to fetal T21 status retrospectively measured prenasal thickness (PT) and nasal bone length (NBL) of T21 and control fetuses at 15–36 weeks’ gestational age on two-dimensional images from all T21-screening ultrasounds from November 2010 to April 2013. ROC curve analysis and its diagnostic values determined the best cut-off value for the ratio. Interobserver reproducibility was assessed. Results Good quality ultrasound profile images were available for 26 fetuses with T21 compared to 91 normal fetuses. The median PT/NBL ratio was 1.28 for T21 and 0.73 for control fetuses ( p < 0.0001). The PT/NBL ratio performed significantly better (AUC 0.99; 95%CI 0.97–1) than either PT (0.82; 0.73–0.91) or NBL (0.91; 0.85–0.98). The optimal PT/NBL ratio cut-off was 0.98, with a sensitivity of 88.5% [76.2–100%] and a specificity of 100%. Interobserver variability was low. Conclusion The PT/NBL ratio is a strong marker for detecting T21 in the second and third trimesters, significantly more effective than either indicator alone. [ABSTRACT FROM AUTHOR]

Objectives To evaluate nasal bone length (NBL), maxilla-nasion-mandible (MNM) angle, fetal profile (FP) line, prenasal thickness (PT), prenasal thickness to nasal bone length (PT:NBL) ratio and prefrontal space ratio (PFSR) as markers of trisomy 18 in the second and third trimesters of pregnancy. Methods The NBL, MNM angle, FP line, PT, PT:NBL ratio and PFSR were measured retrospectively from stored two-dimensional images or three-dimensional volumes of trisomy-18 fetuses, and were compared with our previously reported normal ranges for euploid fetuses. Additional ultrasound findings were noted at initial routine second-trimester scan and at subsequent advanced ultrasound examination performed after referral for karyotyping. Results A total of 43 trisomy-18 fetuses were included in the analysis. At initial examination, median gestational age was 21+2weeks. NBL and PT were correlated with gestational age (P<0.001), but the other markers were not. Mean NBL, MNM angle, PT, PT:NBL ratio and PFSR were 3.76 mm, 16.67°, 4.25 mm, 1.39 and 0.87, respectively. The FP line was zero (normal) in 53.7% of cases and negative (abnormal) in 46.3%. All markers were significantly associated with trisomy 18, with the PT:NBL ratio yielding the highest detection rate (88.4%) followed by NBL (83.7%), MNM angle (56.4%), FP line (46.3%), PT (27.9%) and the PFSR (20.5%) (for a 5% false-positive rate for the continuous variables). Various combinations of the four best markers (NBL, FP line, MNM angle and PT:NBL ratio) yielded detection rates of between 72% and 95%. Structural anomalies were not detected in 22% of fetuses at the initial scan and in 2% at the advanced scan. Conclusions The PT:NBL ratio and NBL are robust second- and third-trimester markers for trisomy 18. A negative FP line has a 0% false-positive rate and the potential to differentiate between trisomy 18 and Down syndrome, as in the latter the FP line is often positive. No major anomaly was observed at the initial scan in about a quarter of trisomy-18 fetuses, underlining the role of second-trimester facial marker evaluation. [ABSTRACT FROM AUTHOR]

ABSTRACT Objectives To evaluate nasal bone length ( NBL), prenasal thickness ( PT), prenasal thickness-to-nasal bone length ( PT-NBL) ratio and prefrontal space ratio ( PFSR) as markers for Down syndrome in the second and third trimesters. Methods NBL, PT, PT-NBL ratio and PFSR were measured retrospectively in stored two-dimensional images or three-dimensional volumes (corrected to the mid-sagittal plane) of fetuses with Down syndrome, which were retrieved from the digital databases of participating units. Measurements were performed on the stored images and volumes by two experienced operators, and the values obtained were compared to our previously reported normal ranges for euploid fetuses in order to assess the detection rates for Down syndrome. Results A total of 159 fetuses with Down syndrome were included in the analysis, six of which were excluded because of inadequate available images. Median maternal age was 36.0 years and median gestational age was 23 + 1 weeks. NBL and PT were correlated with gestational age ( P < 0.001), but the PT-NBL ratio and PFSR were not. Mean NBL, PT, PT-NBL ratio and PFSR were 4.42 mm, 5.56 mm, 1.26 and 0.34, respectively. The nasal bone was absent in 23 (15.4%) cases. As a marker for Down syndrome, the PT-NBL ratio yielded the highest detection rate (86.2%), followed by PFSR (79.7%), PT (63.4%) and NBL (61.9%). All markers were abnormal in 33.6% of cases, whilst all were normal in 4.7%. At least one of the four markers was abnormal in 95.3%, and either the PT-NBL ratio or PFSR was abnormal in 93.8%. Detection rates were not related to gestational age. Conclusions The PT-NBL ratio and PFSR are robust second- and third-trimester markers for Down syndrome. Both provide high detection rates and are easy to use, as the cut-off for normality is constant throughout gestation. Copyright © 2014 ISUOG. Published by John Wiley & Sons Ltd. [ABSTRACT FROM AUTHOR]

Objective: To investigate the ratio of prenasal thickness (PT) to nasal bone length (NBL) in normal and trisomy 21 fetuses in the second and third trimester in Chinese population. Methods: The NBL and PT were measured blindly by using 3D volumes in 143 normal fetuses and 31 trisomy 21 fetuses. Results: The mean PT ( r = 0.83, p = 0.004) and NBL ( r = 0.87, p = 0.0062) both increased with the gestation age, while the PT/NBL ratio ( r = 0.12, p > 0.10) remained stable. There was significant difference between normal and trisomy 21 fetuses ( p < 0.001). If we took the 95th of the normal fetuses as the cut-off value, the detection rate was only 46%. By using ROC curve to evaluate the screening value of PT/NBL ratio, the area under receiver operating characteristic (ROC) curve was 0.88 (95% confidence interval 0.81 to 0.94, p < 0.0001). Conclusions: In Chinese population, the PT/NBL ratio is not a very strong ultrasound marker to predict trisomy 21 fetuses. However, it can be used as an ultrasound marker for Down syndrome screening during the second and third trimester of pregnancy. [ABSTRACT FROM AUTHOR]

Objective: To determine reference range of fetal nasal bone length (NBL) during the second trime ster of pregnancy in a Brazilian population . Methods: This was a retrospective cross-sectional study with 2681 normal singleton pregnancies between 18 and 24 weeks of gestation. The NBL was obtained in the mid-sagittal plane of the fetal face profile using the following landmarks: nasal bone, overlying skin and the tip of the nose. The NBL was measured by placing the calipers in the out-to-out position. To assess the correlation between NBL and gestational age (GA), polynomial equations were calculated, with adjustments by coe fficient of determination (R2). Results: The mean of NBL ranged from 5.72± 0 .87 mm at 18-18± 6 weeks to 7.45± 1.23 mm at 24-24± 6 weeks of pregnancy. We observed a good correlation between NBL and GA, best represented by a linear equation : NBL = 0 .080±0.276*GA (R2 = 0.16). Conclusion: We established a reference range of fetal NBL in the second trim ester of pregnancy in a Brazilian population. [ABSTRACT FROM AUTHOR]

Objectives To assess the feasibility of nasal bone length (NBL), prenasal thickness (PT) and frontomaxillary facial (FMF) angle measurements performed on the same three-dimensional (3D) multiplanar-corrected profile view in healthy second- and third-trimester fetuses, to create reference ranges and to review published measurement techniques. Methods 3D volumes of 219 healthy second- and third-trimester fetuses were retrospectively analyzed. The quality of images and measurability of the markers were assessed with 5-point and 3-point scoring systems, respectively. Measurements of NBL (with care to exclude the frontal bone), PT and FMF were obtained in the exact mid-sagittal plane. Reference ranges were constructed based on measurements from images with high-quality (4 or 5 points) and high measurability (2 or 3 points) scores and compared with those in the most relevant published literature. Results A high-quality score was assigned to 111 images. Among these, a high measurability score was significantly more often achieved for NBL (98.2%) and PT (97.3%) than for the FMF angle (26.1%) ( P < 0.001). Both NBL (NBL = − 6.927 + (0.83 × GA) − (0.01 × GA 2)) and PT (PT = (0.212 × GA) − 0.873) (where GA = gestational age) showed growth with gestation, with less pronounced growth for NBL after 28 weeks. Our reference range for the NBL showed a systematically smaller length than those in other two-dimensional (2D) ultrasound-based publications. The FMF angle measurements that we obtained did not show a significant change with GA. Conclusions NBL and PT are easily measured using 3D ultrasound whereas FMF angle measurement is more challenging. When it is measured in the exact mid-sagittal plane and care is taken to exclude the frontal bone, measurements of the NBL are systematically smaller than those in previous 2D ultrasound-based publications. Copyright © 2012 ISUOG. Published by John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In this paper, the segmentation and extraction of features from ultrasound second trimester fetal images have been presented for early detection of Down syndrome. The region of interest and the edges of the segmented region have been obtained using mean shift analysis and Canny operator, respectively. The prime features such as the nasal bone, the palate and the frontal bone have been segmented for estimating the nasal bone length and frontomaxillary facial angle (FMF). It is observed from the results that the rate of growth of nasal bone length is poor and the FMF angle has been found to increase above 85° for fetus with trisomy 21. This analysis may help the physician for better clinical diagnosis. [ABSTRACT FROM AUTHOR]

Objective: The purpose of this study is to determine the association between fetal nasal bone length (NBL) and gestational age (GA), biparietal diameter (BPD) and head circumference (HC) in women undergoing prenatal assessments and Down syndrome screening. Methods: Cross-sectional data were obtained from 3,003 women with singleton pregnancies who underwent a prenatal ultrasound examination at the Department of Obstetrics and Gynecology, Cheng Hsin General Hospital between August 2006 and July 2009. Results: Statistical analyses involved linear regression. NBL with GA, BPD and HC as measured between 14 and 35 weeks of gestation were linearly related. Conclusions: Using multiple parameters(GA, BPD and HC) to estimate NBL is more accurate than using than using GA or BPD or HC alone, as indicated by the higher predictive value. [ABSTRACT FROM AUTHOR]

Objective: The purpose of the present study was to build a database of reference ranges of fetal nasal bone length (NBL) in a Chinese population. The accuracy rate of detecting Down syndrome was also analyzed using fetal NBL as a marker. Methods: The control group of fetuses included 342 normal singleton pregnancies with no chromosomal or congenital anomalies. The present study was a cross-section study and the control group was used to construct percentile values of NBL from 13 to 29 gestational weeks of age. Two-dimensional ultrasonography was used for the nasal bone studies. Measurements of NBL were collected and each fetus contributed a single value to the reference sample. During the study period, 14 fetuses with Down syndrome were examined. Measurement of fetal NBL was made during amniocentesis, with gestational age ranging from 13 to 19 weeks. Results: From 342 normal fetuses with gestational age ranging from 13 to 29 weeks, reference ranges of NBL were constructed. The reference ranges were constructed from the 100(1 − p)% reference range: , where Ŷ = 25 − exp(3.58 − 0.044 × t + 0.0006 × t2), with Ŷ being the fitted mean of regression model and t being gestational age (weeks). Using fetal NBL, the regression model was Pr(Down syndrome) = exp( W)/[1 + exp( W)], where W = 0.62–4.80 × NBL (multiples of the median) in predicting Down syndrome. Fetal NBL was found to have a sensitivity and specificity of 0.78 and 0.78, respectively, in predicting Down syndrome in the second trimester of pregnancy. Conclusions: Fetal NBL measurement can provide a simple and useful algorithm to predict Down syndrome during the second trimester of pregnancy. [ABSTRACT FROM AUTHOR]

Aim: We carried out a preliminary study to compare the nasal bone length (NBL) and biparietal diameter/NBL (BPD/NBL) ratio between the Japanese and white populations. Methods: Three hundred and fifty nine (359) singleton fetuses of healthy Japanese couples were examined from June 2004 to October 2005. NBL was measured by the strict midsagittal section. The reference range of NBL was established from cross-sectional data between 15 and 25 weeks’ gestation. Results: The success rate of obtaining reliable NBL was 93% (333/356). There were 330 fetuses (93%) available for constructing a reference range from the population. The median NBL increased from 3.2 mm at 15 weeks’ to 7.6 mm at 25 weeks’ gestation. The median of BPD/NBL ratio was 9.01. Conclusions: We demonstrated that NBL was significantly shorter and BPD/NBL was significantly greater in the Japanese population than those in the white and black populations. [ABSTRACT FROM AUTHOR]

The aim of this study was to present our preliminary data about nasal bone measurements at 11-14 weeks of pregnancy. This study was conducted in our prenatal unit between 2000 and 2003. A total of 642 pregnant women (single pregnancies) were enrolled into the study. During the first trimester of pregnancy, crown-rump length, nuchal translucency thickness, and fetal nasal bone length measurements and ductus venosus Doppler images were evaluated. The distribution of absent or small nasal bones in both normal fetuses and in those having some pathological conditions was compared by statistical analysis. p < 0.05 was considered significant. Nasal bone evaluation was successful in 600 of 642 (93.4%) ultrasound examinations. The linear regression line showed a significant positive slope with increasing crown-rump length (r = 0.54, p < 0.001). Absent or small nasal bones were more common in abnormal than in normal fetuses (p = 0.007). It is clear that the fetal nasal bone is becoming a powerful tool in prenatal screening for aneuploidy. Larger studies to be performed in a low-risk population are needed to assess whether the measurement of the nasal bone length provides additional benefits beyond the assessment of the presence or absence of the nasal bone. [ABSTRACT FROM AUTHOR]

Introduction: Sonographic measurements of nasal bone length and prenasal soft tissue thickness are ultrasonographic methods for prenatal screening of Down syndrome., Aim: The aim of the authors was to create a local normogram for nasal bone length and prenasal soft tissue thickness measurements and to test the performance of different statistical methods., Method: Euploid (N = 1500) and trisomy 21 foetuses (N = 10) studied between April 2008 and December 2013 were included. Nasal bone length and prenasal thickness measurements were performed at the Medisono Fetal and Maternal Health Research Centre, Szeged, and cytogenetic tests were performed at the Department of Medical Genetics, University of Szeged, Hungary. Normograms were created with different number of patients (N = 100, 300, 500, 750. 1000 and 1500) and using 3 different statistical methods (linear regression, square-based regression, and box-plot analysis)., Results: The results indicated that at least 1000 measurements are strongly recommended for the normograms. The increase of patient number improved the efficacy of the normograms in each of the 3 statistical methods used for analysis. In general practice box-plots provides a better performance over the other screening methods. However, advanced level screening requires local linear normograms for the best screening results., Conclusion: The use of box-plots is recommended for the use in the daily practice but regression-based normograms are necessary for advanced prenatal screening.