Pelvimetry

Pelvimetry is the assessment of the dimensions and shape of the maternal pelvis to evaluate the capacity of the birth canal to accommodate vaginal delivery. It is used to assess the risk of cephalopelvic disproportion and to guide decisions about labor and delivery.

There are several methods. Clinical pelvimetry relies on physical examination and external measurements and, in some cases, internal measurements via digital examination to estimate the size of the pelvic inlet and outlet. Radiographic pelvimetry uses X-ray imaging to measure the obstetric conjugate, diagonal conjugate, interspinous diameter, transverse diameters, and intertuberous diameter. More recently, computed tomography (CT) pelvimetry and magnetic resonance imaging (MRI) pelvimetry provide more precise three-dimensional assessments; CT involves ionizing radiation, whereas MRI does not.

Indications for pelvimetry are now limited. It may be considered when there is concern for cephalopelvic disproportion due to known pelvic anatomy, prior pelvic fracture or malformation, or specific obstetric history. It is not routinely performed for all pregnancies because many studies show limited predictive value for labor outcome, and fetal size, position, and dynamic labor factors influence delivery.

Risks and limitations include radiation exposure (for radiographic and CT methods), cost and availability for MRI, and observer variability. Pelvimetry provides static measurements that do not capture pelvic dilation during labor. Current practice favors clinical assessment and fetal size estimation, with imaging reserved for selected cases.