Pathophysiology
Clinical meaning
Placenta previa results from implantation of the blastocyst in the lower uterine segment, causing the placenta to partially or completely cover the internal cervical os. As the lower uterine segment thins and the cervix begins to efface in the third trimester, the anchoring placental villi are disrupted from the decidua basalis, exposing maternal spiral arteries and causing hemorrhage. The severity of bleeding depends on the degree of placental separation and the vascularity of the implantation site. Complete previa carries the highest risk of life-threatening hemorrhage. The nurse must perform comprehensive hemorrhage assessment, manage fluid resuscitation, coordinate blood product availability, maintain continuous fetal surveillance, and prepare for emergency cesarean delivery.