1. Placenta previa: abnormal implantation of the placenta in the lower uterine segment; incidence is 0.1-1.0% (higher in subsequent pregnancies); presents with painless vaginal bleeding typically around the 32nd week of gestation; potential for massive blood loss; risk factors include prior uterine scar, prior placenta previa, advanced maternal age, and multiparity.
2. Abruptio placentae: premature separation of a normally implanted placenta after 20 weeks of gestation; incidence is 0.2-2.4%; may present with painful vaginal bleeding, hemorrhagic shock, fetal distress, irritable uterus; potential for massive blood loss (blood loss may be concealed), disseminated intravascular coagulation (DIC), acute renal failure; risk factors: hypertension, uterine abnormalities, history of cocaine abuse.
3. Uterine rupture: incidence: 0.008-0.1% ; majority are spontaneous without explanation; risk factors: previous uterine surgery, prolonged intrauterine manipulation, rapid spontaneous delivery, excessive oxytocin stimulation; may present with sudden onset of breakthrough pain (although most patients with uterine rupture have no pain) with or without vaginal bleeding, abnormalities in fetal heart rate, irritable uterus; potential for massive blood loss.
4. Vasa previa: a condition in which the umbilical card of the fetus passes in front of the presenting part making them vulnerable to trauma during vaginal examination or during artificial rupture of membranes; bleeding here is from the fetal circulation only.
5. Retained placenta: incidence is about 1% of all vaginal deliveries and usually requires manual exploration of the uterus; if no epidural or spinal was used analgesia can be provided with IV opioids, nitrous oxide, or small doses of ketamine; if uterine relaxation is required, and bleeding is minimal, nitroglycerin, 50-100 mcg boluses, can be given (occasionally general anesthesia is required for relaxation).
6. Uterine atony: occurs in 2-5% of patients; treated with IV oxytocin to cause uterine contractions; if this fails, methergine 0.2 mg IM should be given. If these measures fail, then emergency hysterectomy or internal iliac artery ligation may be necessary.
7. Laceration of the vagina, cervix or perineum are common.
8. Uterine inversion is very rare and is a true obstetrical emergency; general anesthesia is generally required to allow immediate uterine relaxation; these patients can exsanguinate rapidly.
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