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Normal Fetal Pelvis: Important Factors for Morphometric Characterization with US¹

¹ From the Department of Radiology, Duke University Medical Center, Box 3808, Rm 2526, Blue Zone, South, Durham, NC 27710. Received February 15, 1999; revision requested April 5; revision received August 26; accepted August 30. Address correspondence to M.A.K.

PURPOSE: To prospectively evaluate iliac angle and iliac length in a large number of normal fetuses and to identify factors that may influence these measurements.

MATERIALS AND METHODS: At antenatal ultrasonography (US) in 356 fetuses, the iliac angle and iliac length were measured at two axial levels (superior and inferior). In mixed linear models, the statistical significance and magnitude of effect on the measurement of iliac angle and iliac length were estimated for gestational age, fetal sex, maternal diabetes status, axial level, and spine position relative to the transducer.

RESULTS: Statistically significant effects were found for gestational age, axial level, and spine orientation but not for fetal sex or maternal diabetes status. The iliac angle was found to decrease by 15.7° from the superior to inferior portion of the pelvis, decrease by approximately 0.37°/wk, and decrease by as much as 15.6° when the spine is directed to the side. Iliac length was found to increase by 0.8 mm/wk from 13 weeks to term, decrease by 1.2 mm from the superior to the inferior portion of the pelvis, and increase by as much as 1.29 mm when the spine is not directly subjacent to the transducer.

CONCLUSION: The axial level of measurement, gestational age, and spine orientation must be accounted for if these morphometric indexes are used to discriminate fetuses with and those without Down syndrome.

Index terms: Down syndrome, 856.1298, 856.873 • Fetus, abnormalities, 856.873 • Fetus, skeletal system, 856.873 • Fetus, US, 85.1298 • Pelvis, measurement, 44.1298, 856.873

This article has been cited by other articles:

				M. A. Kliewer, B. S. Hertzberg, K. S. Freed, P. J. McNally, and D. M. DeLong The Anterior Iliac Separation: Alternative Index for Pelvic Morphometry in Fetuses with Down Syndrome Am. J. Roentgenol., April 1, 2001; 176(4): 1003 - 1007. [Abstract] [Full Text] [PDF]