However, among known causes of significant bleeding, placenta previa and placental abruption are the two most common etiologies. Placenta previa usually is associated with painless vaginal bleeding, although uterine contractions may be present. The diagnosis is best confirmed by an ultrasound scan. Factors associated with an increased risk of placenta previa include multiparity, advancing maternal age, previous cesarean deliveries, and induced abortion. Placenta previa may be associated with placenta accreta, especially if a patient has had a previous cesarean delivery.
Management depends on the amount of persistent bleeding and the gestational age at presentation.
Tocolytics of the beta-mimetic class are generally not recommended in women with significant bleeding because these tocolytics may be associated with tachycardia and hypotension and their efficacy is questionable. There are similar problems with the calcium channel blockers. The initial episode of bleeding in patients with placenta previa is often not excessive, and it is common for patients to bleed intermittently in the third trimester. Thus, in the patient remote from term, all efforts should be directed toward conservative care with restricted activity so that the fetus can mature. Because a significant number of newborns delivered after a bleeding episode caused by placenta previa have hypovolemia or anemia or both, there is an increasing tendency to deliver them by cesarean birth once they are mature.