Normal fetal pelvis: important factors for morphometric characterization with US.
OBJECTIVE
To prospectively evaluate iliac angle and iliac length in a large number of normal fetuses and to identify factors that may influence these measurements.


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 degrees from the superior to inferior portion of the pelvis, decrease by approximately 0.37 degrees /wk, and decrease by as much as 15.6 degrees 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.


CONCLUSIONS
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.
Kliewer
M A
MA
Department of Radiology, Duke University Medical Center, Rm 2526, Blue Zone, South, Durham, NC 27710, USA.
Hertzberg
B S
BS
Freed
K S
KS
McNally
P J
PJ
DeLong
D M
DM
D000649:Amniocentesis; D000886:Anthropometry; D015986:Confounding Factors, Epidemiologic; D004314:Down Syndrome / Q000000981:diagnostic imaging; D005260:Female; D005315:Fetal Diseases / Q000000981:diagnostic imaging; D005544:Forecasting; D005865:Gestational Age; D006801:Humans; D007085:Ilium / Q000000981:diagnostic imaging / Q000196:embryology*; D016014:Linear Models; D008297:Male; D010384:Pelvic Bones / Q000000981:diagnostic imaging / Q000196:embryology; D011247:Pregnancy; D011254:Pregnancy in Diabetics / Q000145:classification; D011446:Prospective Studies; D012737:Sex Factors; D013131:Spine / Q000000981:diagnostic imaging / Q000196:embryology; D014159:Transducers; D016216:Ultrasonography, Prenatal / Q000295:instrumentation / Q000379:methods