Sonographic measurement of the fetal iliac angle cannot be used alone as a marker for trisomy 21

The fetal iliac wings angle was studied in 255 fetuses before amniocentesis at 16.7 weeks (+/- 1.3), using a sonographic axial view of the fetal pelvis. The measurement could be performed in 208 fetuses (81.6%), of whom 4 had trisomy 21 (T 21). The mean iliac angle was greater in fetuses with T 21 than in normal fetuses (69.8 degrees vs. 88.7 degrees; p = 0.03). This measurement is subject to significant intra- and interexaminer variability (interclass correlation coefficient: 0.65 and 0.23, respectively). When a 90 degrees value is used as a threshold, specificity, sensitivity, positive and negative predictive values are, respectively, 80, 75, 7. 0 and 99.4%. The 20% rate of false-positives rules out the use of this measurement as the sole criterion for the indication of amniocentesis for T 21 antenatal diagnosis.