CT Pelvimetry

Pelvimetry is occasionally requested when vaginal delivery is being considered for breech presentation (especially in a primagravida) or for patients with suspected cephalopelvic disproportion, although reports on the utility of pelvimetry are conflicting and the reproducibility of pelvimetry measurements has also been questioned [1-3]. Pelvimetry can be performed by conventional radiography, CT, or MRI [4]. While MRI has the theoretical advantage of not using ionizing radiation, the fetal dose from a limited CT pelvimetry study (low doses lateral and frontal digital radiographs with a single axial slice through the femoral heads to measure interspinous diameter) is under 0.1 rad. Even assuming the worse case scenario that the dose is 0.1 rad and that such a dose is as dangerous as radiation earlier in pregnancy, the risk of fatal childhood cancer would only be increased by 2%, a minimal risk. For such reasons, if pelvimetry is considered appropriate, it is reasonable to perform pelvimetry by CT rather than MRI.

Key point: Pelvimetry can be performed either by low dose CT or by MRI, and written informed consent is not required.