Fetal iliac angle measurements by three-dimensional sonography

Objective To determine the technical reliability of fetal iliac angle measu rements by three-dimensional sonography as a prenatal marker for Down syndr ome. Methods Three-dimensional multiplanar views of the fetal pelvis were used t o standardize iliac angle measurements from 35 normal second-trimester preg nancies. Measurement reliability for a single examiner and between two diff erent examiners were analyzed by intraclass correlation. Normal iliac angle measurements were compared to those obtained from 16 fetuses with trisomy 21. Results The mean axial angle for normal fetuses was 79 +/-5.5 degrees, whic h was significantly less than that observed in fetuses with trisomy 21 (87. 7 +/-4.9 degrees) (P < 0.001). Iliac angles did not correlate with gestatio nal age. Axial angles were reproducible between two examiners who measured the same multiplanar view of the pelvis. Inter- and intraobserver reliabili ty were also acceptable after a standardized multiplanar view was independe ntly obtained by each examiner (intraclass correlation = 0.91 for both). Co ronal angles were unreliable because of difficulties with finding a reprodu cible measurement plane. For a false-positive rate of 5%, an axial angle th reshold of 87<degrees> correctly identified 56% of fetuses with trisomy 21. Conclusion Axial iliac angle measurements are reliable by standardized thre e-dimensional multiplanar views of the pelvis and can be used to identify s ome fetuses at increased risk for trisomy 21.