Obstetric MR pelvimetry: reference values and evaluation of inter- and intraobserver error and intraindividual variability.
OBJECTIVE
To establish obstetric magnetic resonance (MR) pelvimetric reference values in a large study population and stratify them according to delivery modality and to determine the intra- and interobserver error and intraindividual variability of MR pelvimetric assessment in volunteers.


METHODS
MR pelvimetric data were retrospectively reviewed in 781 women (mean age, 28.9 years +/- 5.2 [SD]) clinically referred, and the data were correlated to obstetric history to derive normative values. Five observers assessed results of multiple MR pelvimetric examinations in 10 female volunteers (mean age, 34.7 years +/- 6.0; eight nullipara, two primipara) to provide data for measurement error analysis.


RESULTS
All values were higher in the spontaneous vaginal delivery subgroup (n = 100) and lower in the cesarean section or vacuum extraction subgroup (n = 130; intersubgroup difference, P <.001, Mann-Whitney U test). Pelvimetric parameters in the group undergoing spontaneous vaginal delivery were as follows: obstetric conjugate, 121.7 mm +/- 8.6; interspinous distance, 112.3 mm +/- 7.9; intertuberous distance, 120.6 mm +/- 11.3; transverse diameter, 129.5 mm +/- 8.7; and sagittal outlet, 115.8 mm +/- 9.9. In the volunteer study, intraobserver, interobserver, and intraindividual reliabilities were high for the obstetric conjugate (0.94-0.96), interspinous distance (0.92-0.95), and transverse diameter (0.95-0.98) but low for intertuberous distance (0.64-0.87) and sagittal outlet (0.66-0.85).


CONCLUSIONS
Pelvimetric dimensions are smaller in women undergoing cesarean section or vacuum extraction than they are in those delivering vaginally. The pelvimetric parameters associated with the largest measurement errors are intertuberous distance and sagittal outlet.
Keller
Thomas M
TM
Institute of Diagnostic Radiology, University Hospital, Zurich, Switzerland.
Rake
Annett
A
Michel
Sven C A
SC
Seifert
Burkhardt
B
Efe
Gul
G
Treiber
Karl
K
Huch
Renate
R
Marincek
Borut
B
Kubik-Huch
Rahel A
RA
D000293:Adolescent; D000328:Adult; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D015588:Observer Variation; D010387:Pelvimetry / Q000379:methods* / Q000706:statistics & numerical data*; D011247:Pregnancy; D012016:Reference Values; D012189:Retrospective Studies