North American Registry of Midwives (NARM) Practice Exam

The only true test for cephalopelvic disproportion (CPD) is labor. While various imaging techniques such as ultrasound and pelvic x-rays can provide information about the size and shape of the pelvis and the fetus, they do not definitively establish whether a fetus will fit through the birth canal during the actual process of labor. In labor, the dynamics of the contractions, the position of the fetus, and the mother’s ability to progress through labor all come into play. It is in this setting that CPD can be directly observed through the progress of labor. If a woman is unable to progress despite effective contractions and a reasonable amount of time, it can then be concluded that there is a disproportion between the fetal head size and the pelvic dimensions. Patient history may provide some insights into potential risk factors for CPD, but it lacks the objective assessment that labor provides. Consequently, true determination of CPD can only be made during the labor experience, making it the definitive test.