Interobserver variability of the measurement of fetal nasal bone length between 11+0 and 13+6 gestation weeks among experienced and inexperienced sonographers

Image-scoring system for crown-rump length measurement

OBJECTIVE

To develop and evaluate an objective image-scoring system for crown-rump length (CRL) measurements and to determine how this compares with subjective assessment.

METHODS

A total of 125 CRL ultrasound images were selected from the database of the International Fetal and Newborn Growth Consortium for the 21(st) Century study group. Two reviewers, who were blinded to the operators' and to each others' results, evaluated all images both subjectively and objectively. Subjective evaluation consisted of rating an image as acceptable or unacceptable, while objective evaluation was based on six criteria. Reviewer differences for both the subjective and objective evaluations were compared using percentage of agreement and adjusted kappa values.

RESULTS

The distribution of individual scores and differences between subjective and objective evaluation for the two reviewers was similar. Overall agreement between the reviewers was higher for objective evaluation (95.2%; adjusted κ, 0.904), than for subjective evaluation (77.6%; adjusted κ, 0.552). There was a high level of agreement for horizontal position (κ = 0.951), magnification (κ = 0.919), visualization of crown and rump (κ = 0.806) and caliper placement (κ = 0.756), while agreement for mid-sagittal section (κ = 0.629) and neutral position (κ = 0.565) were moderate and poor, respectively.

CONCLUSION

The proposed six-point scoring system for CRL image rating is more reproducible than is subjective evaluation and should be considered as a method of quality assessment and audit.

The usefulness of volume NT software in measuring the fetal nasal bone at 11 to 13 + 6 weeks of gestation

OBJECTIVE

The objective of this study is to investigate the reproducibility of 3D ultrasound to measure the fetal nasal bone (NB) at first trimester.

METHODS

A group of singleton viable pregnancies attending the 11 to 13 + 6 weeks aneuploidy screening at the University of Bologna were prospectively selected. For each patient, fetal NB was measured by 2D ultrasound. Subsequently, a 3D ultrasound of the fetal head was acquired, and fetal NB was measured by offline analysis using the volume nuchal translucency software. The correlation between 2D and 3D ultrasounds and the reproducibility of fetal NB measurement at 3D ultrasound were assessed.

RESULTS

Overall, 161 Caucasian women were included in the study. At 3D ultrasound, NB measurement showed an excellent intraobserver [Oper 1, intraclass correlation coefficient (ICC) = 0.98; Oper 2, ICC = 0.921] and interobserver agreement (rc = 0.92). The agreement between 2D and 3D measurements was moderate (rc = 0.77).

CONCLUSIONS

A 3D ultrasound supported by the volume nuchal translucency software may provide reliable measurements of the fetal NB in the first trimester.

Normative values of fetal nasal bone lengths of Turkish singleton pregnancies in the first trimester

OBJECTIVE

Evaluation of nasal bone improves the performance of first-trimester screening for trisomy 21. In this retrospective study we aimed to determine normative values related to the measurement of nasal bone length of the Turkish population during the first trimester ultrasonographic fetal screening.

MATERIAL AND METHODS

Medical records of singleton pregnancies, whose first trimester fetal screening was performed between 2004 and 2010, were evaluated retrospectively. Pregnancies with any detected/suspicious anatomical or genetic fetal anomalies, biochemical abnormalities, increased nuchal translucency measurements, and pregnancies of artificial reproduction techniques were excluded from data analyses. Mean±standard deviation, median and percentile values of the length of nasal bone were calculated separately for 11(0-6), 12(0-6) and 13(0-6) gestational weeks.

RESULTS

Nasal bone could be visualized in 99.6% of the included 1762 singleton pregnancies. In 16.5% of the cases nasal bones were only noted as present or absent. Mean maternal age was 29.67±4.50 years and mean gestational age was 12.54±0.61 weeks. Median values of nasal bone lengths were 1.7, 1.9, and 2.2 mm for 11(0-6), 12(0-6) and 13(0-6) gestational weeks respectively. Nasal bone length (NBL) increased linearly with advancing gestational age and CRL. NBL (mm)=[0.298xGestational Age (week)]-1.779, R(2)=0.318; p<0.001; NBL (mm)= [0.023 × CRL (mm)] + 0.520, R(2)=0.331; p<0.001.

CONCLUSION

The present study presents normative values of nasal bone in the first trimester screening of normal singleton pregnancies of Turkish population. Nasal bone length increases with advancing gestational age and CRL.