Summarize the major causes of third-trimester bleeding.
A “bloody show” is the most common cause of bleeding during the third trimester. This occurs during labor and is due to effacement and dilatation of the cervix. Placental problems are responsible for most pathologic third-trimester bleeding, of which placental abruption and placenta previa account for the majority. Cervical bleeding due to polyps and carcinoma is much less com-mon. Vasa previa, umbilical cord vessels traveling within the placental membranes and covering the cervical os, is a rare cause of third-trimester bleeding. Other rare causes of third-trimester bleeding are maternal coagulopathy, due to preeclampsia, and intrauterine fetal demise (Table 61.1).