Also found in: Acronyms.
a radiographic examination used to determine the dimensions of the bony pelvis of a pregnant woman and, if possible, the biparietal diameter of her baby's head. It is performed when doubt exists as to whether the head can pass safely through the pelvis in labor. Images of the pelvis and the baby are projected radiographically onto film. After the film is developed, the images are measured. The measurements are corrected for distortion, and the true dimensions of the birth canal and head are calculated. Often the cephalopelvic relationship cannot be accurately evaluated from the films because the baby's head may be positioned in such a way that the biparietal diameter cannot be visualized. Because minor degrees of cephalopelvic disproportion are often overcome safely in labor by molding of the fetal skull and because major disproportions may be detected by clinical pelvimetry without x-rays, the value of x-ray pelvimetry is frequently judged to be insufficient to warrant the risk of radiation exposure. Other diagnostic tools, among them ultrasonography, often provide the necessary information with less apparent risk. Compare clinical pelvimetry. See also cephalopelvic disproportion, contraction, dystocia.