Fetal iliac angle measurements by three-dimensional sonography

Abstract

Objective: To determine the technical reliability of fetal iliac angle measurements by three-dimensional sonography as a prenatal marker for Down syndrome.

Methods: Three-dimensional multiplanar views of the fetal pelvis were used to standardize iliac angle measurements from 35 normal second-trimester pregnancies. Measurement reliability for a single examiner and between two different 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, which 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 gestational age. Axial angles were reproducible between two examiners who measured the same multiplanar view of the pelvis. Inter- and intraobserver reliability were also acceptable after a standardized multiplanar view was independently obtained by each examiner (intraclass correlation = 0.91 for both). Coronal angles were unreliable because of difficulties with finding a reproducible measurement plane. For a false-positive rate of 5%, an axial angle threshold of 87 degrees correctly identified 56% of fetuses with trisomy 21.

Conclusion: Axial iliac angle measurements are reliable by standardized three-dimensional multiplanar views of the pelvis and can be used to identify some fetuses at increased risk for trisomy 21.