partial placenta previa, placenta previa in which the placenta is implanted in the lower uterine segment and partially covers the internal os of the uterine cervix. As the cervix dilates in labor, the part of the placenta that lies over the cervix is separated, causing bleeding from the villous spaces of the uterine wall. Depending on the degree of separation, the bleeding may be scant or severe, resulting in hemorrhage that is life-threatening to the mother and the baby. Treatment may require cesarean section if the pressure of the presenting part of the baby is not sufficient to tamponade the bleeding site, stopping the hemorrhage. Diagnosis of partial placenta previa may be made before bleeding occurs by ultrasonic visualization or digital palpation in the course of prenatal examination. See also marginal placenta previa, placenta previa.
