Reliability of radiographic pelvimetry. A methodological study.

The purpose of this study was to assess the reliability of radiographic pelvimetry. 48 radiologists were asked to estimate the pelvic inlet and outlet diameters from copies of 20 pelvimetry radiographs. We found that every third patient will have the sum of her pelvic outlet over- or underestimated by at least 4 mm, and 3% by more than 10 mm. The random measurement error of the sum of the pelvic outlet is about four times greater than the systematic error. The random error of the sagittal outlet diameter contributes to almost half of the total measurement error of the pelvic outlet sum. The measurement values of radiographic pelvimetry are often expressed in mm, which may give an impression of exactness that is obviously not well founded. Only in a few cases where the measurements suggest a severe feto-pelvic disproportion is it justified to do an elective cesarean section on the basis of radiographic pelvimetry only.