DYSMORPHOLOGIC FEATURES OF THE FETAL PELVIS IN DOWN-SYNDROME - PRENATAL SONOGRAPHIC DEPICTION AND DIAGNOSTIC IMPLICATIONS OF THE ILIAC ANGLE

PURPOSE: To determine whether the axial pelvic profile is morphologica lly different in fetuses with Down syndrome from those with a normal k aryotype. MATERIALS AND METHODS: Pelvic images were selected from ultr asound studies in 27 fetuses with trisomy 21 and in 135 fetuses with a normal karyotype. An observer blinded to study results measured the a ngle formed by the convergence of lines drawn tangent to the wing of t he ilium. This angle was measured prospectively in 20 normal fetuses b y four independent observers to estimate variability. RESULTS: The ili ac bones could be assessed in 19 fetuses with trisomy 21 and in 87 fet uses with a normal karyotype. Between 15 and 20 weeks of gestation, th e mean iliac angle was 60 degrees in normal fetuses and 75 degrees in fetuses with Down syndrome (P < .001). Intra- and interobserver correl ation coefficients were .70 and .62, respectively. The greatest variab ility in results was among fetuses (estimated variance, 72.5); smaller variance was seen with repeat measurements in the same fetus (34.7) a nd with measurements by different observers CONCLUSION: The mean iliac angle in fetuses with Down syndrome is larger than that in fetuses wi thout Down syndrome and may aid in weighing the risks of trisomy 21 ag ainst the risks of performing amniocentesis.