Fetal iliac angle measurements by three-dimensional sonography.
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.


CONCLUSIONS
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.
Lee
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W
Division of Fetal Imaging, Department of Obstetrics and Gynecology, William Beaumont Hospital, 3601 West Thirteen Mile Road, Royal Oak, MI 48073-6769, USA. wlee@beaumont.edu
Blanckaert
K
K
Bronsteen
R A
RA
Huang
R
R
Romero
R
R
D000328:Adult; D004314:Down Syndrome / Q000000981:diagnostic imaging*; D005260:Female; D005865:Gestational Age; D006801:Humans; D007085:Ilium / Q000000981:diagnostic imaging* / Q000196:embryology*; D021621:Imaging, Three-Dimensional; D011247:Pregnancy; D016216:Ultrasonography, Prenatal