cephalopelvic disproportion (CPD) [Gk, kephale + L, pelvis, basin, dis, opposite of, proportio, similarity] , an obstetric condition in which a baby’s head is too large or a mother’s birth canal too small to permit normal labor or birth. In relative CPD, the size of the baby’s head is within normal limits but larger than average or the size of the mother’s birth canal is within normal limits but smaller than average, or both; relative CPD is often overcome by molding of the head, the forces of labor, or the use of forceps to effect delivery. In absolute CPD, the baby’s head is markedly or abnormally enlarged or the mother’s birth canal is markedly or abnormally contracted, making vaginal delivery impossible. See also clinical pelvimetry, protraction disorders, dystocia.
