Dysmorphologic features of the fetal pelvis in Down syndrome: prenatal sonographic depiction and diagnostic implications of the iliac angle.

Abstract

To determine whether the axial pelvic profile is morphologically different in fetuses with Down syndrome from those with a normal karyotype. Pelvic images were selected from ultrasound studies in 27 fetuses with trisomy 21 and in 135 fetuses with a normal karyotype. An observer blinded to study results measured the angle formed by the convergence of lines drawn tangent to the wing of the ilium. This angle was measured prospectively in 20 normal fetuses by four independent observers to estimate variability. The iliac bones could be assessed in 19 fetuses with trisomy 21 and in 87 fetuses with a normal karyotype. Between 15 and 20 weeks of gestation, the mean iliac angle was 60 degrees in normal fetuses and 75 degrees in fetuses with Down syndrome (P < .001). Intra- and interobserver correlation coefficients were .70 and .62, respectively. The greatest variability in results was among fetuses (estimated variance, 72.5); smaller variance was seen with repeat measurements in the same fetus (34.7) and with measurements by different observers (9.1). The mean iliac angle in fetuses with Down syndrome is larger than that in fetuses without Down syndrome and may aid in weighing the risks of trisomy 21 against the risks of performing amniocentesis.