F. I. Vos

Prenasal thickness-to-nasal bone length ratio: a strong and simple second- and third-trimester marker for trisomy 21

To study the ratio of prenasal thickness (PT) to nasal bone length (NBL) in normal and trisomy‐21 fetuses in the second and third trimesters of pregnancy.

Three-dimensional ultrasound imaging and measurement of nasal bone length, prenasal thickness and frontomaxillary facial angle in normal second- and third-trimester fetuses.

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.

Nasal bone length, prenasal thickness, prenasal thickness-to-nasal bone length ratio and prefrontal space ratio in second- and third-trimester fetuses with Down syndrome

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.

Facial profile markers in second- and third-trimester fetuses with trisomy 18

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.

Is 3D technique superior to 2D in Down syndrome screening? Evaluation of six second and third trimester fetal profile markers

The objective of this article is to investigate whether in the clinical setting of second trimester ultrasound (US) investigations, 3D multiplanar correction prior to the measurement of Down syndrome (DS) facial markers (nasal bone length, prenasal thickness, fetal profile line, maxilla‐nasion‐mandible angle, prenasal thickness to nasal bone length ratio, and prefrontal space ratio) is superior to subjective judgment of a correct midsagittal plane by 2D technique.

Trends in Serial Measurements of Ultrasound Markers in Second and Third Trimester Down Syndrome Fetuses

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.

OP09.02: How flat is the profile, measured with the MNM angle, in second and third trimester trisomy 21 fetuses?

Objectives: The MNM angle, defined as the angle between the lines maxilla-nasion and mandible-nasion in the exact median plane, enables objective evaluation of the anteroposterior relationship of the jaws. Fetuses with trisomy 21 are known to have a flat profile caused by underdevelopment of the maxilla. This study evaluates the MNM angle in second and third trimester trisomy 21 fetuses. Methods: Databases were searched for digitally stored 3D-volumes and images of the fetal profile in second and third trimester trisomy 21 fetuses. The MNM angle was measured in good median 2D images and in by multiplanar mode corrected images from 3Dvolumes. Measurements in the trisomy 21 fetuses were compared with the reference range derived from 3D-volumes of 241 euploid fetuses in an earlier study. Volumes and images were acquired by Voluson 730 Expert and Voluson E8 (GE Healthcare). Results: In the 241 euploid fetuses (median gestational age: 24+5 weeks, range: 15+4–35+4 weeks) the mean MNM angle was 13.53◦ (95% CI: 13.28◦–13.78◦, range: 8.96◦–19.58◦). The MNM angle was measured in 19 trisomy 21 fetuses (15 on 3D-volumes, 4 on 2D images) at a median of 21+6 weeks (range: 14–34+5 weeks). In trisomy 21 fetuses the mean MNM angle was 10.74◦ (95% CI: 9.38◦–12.10◦, range: 6.19◦–14.99◦) and, similarly to euploid fetuses, did not change with gestational age (r = 0.22, P = 0.36). The MNM angle was significantly smaller in trisomy 21 fetuses (P = 0.001) and was below the mean or 5th percentile in 84.2% and 36.8% of the cases, respectively. Conclusions: The MNM angle is significantly smaller in second and third trimester trisomy 21 fetuses and in 37% of the cases is below the 5th percentile. Measurement of the MNM angle may be used for counselling together with other markers, when trisomy 21 is suspected.

OP09.10: 3D ultrasound imaging and reproducibility of nasal bone length, prenasal thickness and fronto‐maxillary facial angle in normal second and third trimester fetuses

Objectives: To create reference ranges for nasal bone length (NBL) and prenasal thickness (PT) based on measurements performed on 3D to the exact median plane corrected profile views and to examine their mutual relationship in normal second and third trimester fetuses. Methods: 3D profile volumes of 200 normal fetuses at 15–33 weeks gestation were reviewed and adjusted by multiplanar mode to the correct median profile. The nasal bone was measured from the nasion to the most anterior end of the ossification line. The frontal bone extends behind the nasal bone, therefore care was taken not to add this part of the frontal bone to the measurement of NBL as this would erroneously increase the measurement. The PT was measured as the shortest distance between the nasion and the frontal skin. Results: Good visualization of the landmarks and good NBL and PT measurements were obtained in 109 cases and 108 cases, respectively. In 106 cases, both NBL and PT could be measured in the same profile. NBL increased with gestational age, from 3.2 mm at 15 weeks to 9.0 mm at 33 weeks (NBL followed a second order polynomial trend). PT increased with gestational age from 2.3 mm at 15 weeks to 6.1 mm at 33 weeks (PT followed a first order polynomial trend). NBL and PT were highly correlated (r = 0.83, P < 0.001). Linear regression analysis showed that NBL contributes to 46% of PT increase (r = 0.46, P < 0.001). Conclusions: These are the first reference range for NBL and PT constructed on by multiplanar view corrected exact median profiles of normal second and third trimester fetuses. The range extends to the third trimester and both parameters are measured in the same fetus. Redefinition of the measurement technique for the NBL by excluding erroneous inclusion of part of the frontal bone, produces systematically smaller measurements than previously published reference ranges. NBL and PT increase linearly with gestation, with less steep increase for the NBL after 28 weeks.

OP09.09: Use of 3D ultrasound in visualization and measurement of nasal bone length and prenasal thickness in normal second and third trimester fetuses

Objectives: To create reference ranges for nasal bone length (NBL) and prenasal thickness (PT) based on measurements performed on 3D to the exact median plane corrected profile views and to examine their mutual relationship in normal second and third trimester fetuses. Methods: 3D profile volumes of 200 normal fetuses at 15–33 weeks gestation were reviewed and adjusted by multiplanar mode to the correct median profile. The nasal bone was measured from the nasion to the most anterior end of the ossification line. The frontal bone extends behind the nasal bone, therefore care was taken not to add this part of the frontal bone to the measurement of NBL as this would erroneously increase the measurement. The PT was measured as the shortest distance between the nasion and the frontal skin. Results: Good visualization of the landmarks and good NBL and PT measurements were obtained in 109 cases and 108 cases, respectively. In 106 cases, both NBL and PT could be measured in the same profile. NBL increased with gestational age, from 3.2 mm at 15 weeks to 9.0 mm at 33 weeks (NBL followed a second order polynomial trend). PT increased with gestational age from 2.3 mm at 15 weeks to 6.1 mm at 33 weeks (PT followed a first order polynomial trend). NBL and PT were highly correlated (r = 0.83, P < 0.001). Linear regression analysis showed that NBL contributes to 46% of PT increase (r = 0.46, P < 0.001). Conclusions: These are the first reference range for NBL and PT constructed on by multiplanar view corrected exact median profiles of normal second and third trimester fetuses. The range extends to the third trimester and both parameters are measured in the same fetus. Redefinition of the measurement technique for the NBL by excluding erroneous inclusion of part of the frontal bone, produces systematically smaller measurements than previously published reference ranges. NBL and PT increase linearly with gestation, with less steep increase for the NBL after 28 weeks.

OP09.04: PT is 2/3 of NBL, this easy to use ratio is significant higher in trisomy 21 fetuses in the second and third trimester

Objectives: The MNM angle, defined as the angle between the lines maxilla-nasion and mandible-nasion in the exact median plane, enables objective evaluation of the anteroposterior relationship of the jaws. Fetuses with trisomy 21 are known to have a flat profile caused by underdevelopment of the maxilla. This study evaluates the MNM angle in second and third trimester trisomy 21 fetuses. Methods: Databases were searched for digitally stored 3D-volumes and images of the fetal profile in second and third trimester trisomy 21 fetuses. The MNM angle was measured in good median 2D images and in by multiplanar mode corrected images from 3Dvolumes. Measurements in the trisomy 21 fetuses were compared with the reference range derived from 3D-volumes of 241 euploid fetuses in an earlier study. Volumes and images were acquired by Voluson 730 Expert and Voluson E8 (GE Healthcare). Results: In the 241 euploid fetuses (median gestational age: 24+5 weeks, range: 15+4–35+4 weeks) the mean MNM angle was 13.53◦ (95% CI: 13.28◦–13.78◦, range: 8.96◦–19.58◦). The MNM angle was measured in 19 trisomy 21 fetuses (15 on 3D-volumes, 4 on 2D images) at a median of 21+6 weeks (range: 14–34+5 weeks). In trisomy 21 fetuses the mean MNM angle was 10.74◦ (95% CI: 9.38◦–12.10◦, range: 6.19◦–14.99◦) and, similarly to euploid fetuses, did not change with gestational age (r = 0.22, P = 0.36). The MNM angle was significantly smaller in trisomy 21 fetuses (P = 0.001) and was below the mean or 5th percentile in 84.2% and 36.8% of the cases, respectively. Conclusions: The MNM angle is significantly smaller in second and third trimester trisomy 21 fetuses and in 37% of the cases is below the 5th percentile. Measurement of the MNM angle may be used for counselling together with other markers, when trisomy 21 is suspected.