Placenta Previa

Placenta previa is an obstetric complication that occurs in the second and third trimesters of pregnancy. It may cause serious morbidity and mortality to both the fetus and the mother. It is one of the leading causes of vaginal bleeding in the second and third trimesters.

Placenta previa.

Placenta previa.

Placenta previa.

Placenta previa.

Placenta previa is generally defined as the implantation of the placenta over or near the internal os of the cervix.

  • Total placenta previa occurs when the internal cervical os is completely covered by the placenta.
  • Partial placenta previa occurs when the internal os is partially covered by the placenta.
  • Marginal placenta previa occurs when the placenta is at the margin of the internal os.
  • Low-lying placenta previa occurs when the placenta is implanted in the lower uterine segment. In this variation, the edge of the placenta is near the internal os but does not reach it.
  • A recent study concluded that more than two thirds of women with a distance of more than 10 mm from the placental edge to cervical os have vaginal delivery without an increased risk of hemorrhage.1

Pathophysiology

The exact etiology of placenta previa is unknown. The condition may be multifactorial and is postulated to be related to multiparity, multiple gestations, advanced maternal age, previous cesarean delivery,2 previous abortion, and possibly, smoking. Unlike first trimester bleeding, second and third trimester bleeding is usually secondary to abnormal placental implantation.

Frequency

United States

Placenta previa complicates approximately 5 of 1,000 deliveries and has a mortality rate of 0.03%. Data recorded from 1989-1997 indicated placenta previa occurs in 2.8 per 1000 live births in the United States.

Mortality/Morbidity

The maternal mortality rate secondary to placenta previa is approximately 0.03%. Babies born to women with placenta previa tend to weigh less than babies born to women without placenta previa. The risk of neonatal mortality is higher for placenta previa babies compared with pregnancies without placenta previa. The great majority of deaths are related to uterine bleeding and the complication of disseminated intravascular coagulopathy. In early pregnancy, a partial previa can often self-correct as the uterus enlarges and the placental site moves cephalad.

Race

Significance of race is somewhat controversial. Some studies suggest an increased risk of placenta previa among blacks and Asians, whereas other studies cite no difference.

Age

Women older than 30 years are 3 times more likely to have placenta previa than women younger than 20 years.

Clinical

History

Placenta previa is one of the leading causes of vaginal bleeding.

  • Vaginal bleeding is apt to occur suddenly during the third trimester.
  • Bleeding is usually bright red and painless. Some degree of uterine irritability is present in about 20% of the cases.
  • Initial bleeding is not usually profuse enough to cause death; it spontaneously ceases, only to recur later.
  • The first bleed occurs (on average) at 27-32 weeks’ gestation.
  • Contractions may or may not occur simultaneously with the bleeding.

Physical

  • Profuse hemorrhage
  • Hypotension
  • Tachycardia
  • Soft and nontender uterus
  • Normal fetal heart tones (usually)
  • Vaginal and rectal examinations
    • Do not perform these examinations in the ED because they may provoke uncontrollable bleeding.
    • Perform examinations in the operating room under double set-up conditions (ie, ready for emergent cesarean delivery).

Emergency Department Care

  • Because of the potential morbidity and mortality secondary to profuse bleeding, obtain immediate gynecologic consultation, if available. Before gynecologic consultation or transfer, the hemodynamic stability of the patient should be addressed. This includes the establishment of 2 large-bore intravenous access lines with intravenous crystalloids or blood products, as necessary.
  • Obtain continuous fetal monitoring, if available.
  • If the fetus is preterm and immediate delivery is unnecessary (eg, fetus <37 weeks’ gestation and hemorrhage not present), the patient may be treated expectantly on an outpatient basis.
  • If the fetus is reasonably mature (ie, >37 weeks’ gestation) and the patient is in labor or if severe hemorrhage is present, therapy is directed at the delivery of the fetus. The patient should receive crystalloids and/or blood, and the patient should be transferred to the operating room with double set-up conditions.
  • A trial of labor may be considered for anterior marginal previa, including oxytocin (Pitocin) augmentation.
  • Guidelines for the diagnosis and management of placenta previa have been established.3,4

Consultations

  • Consult an obstetrician.

Medication

The goal of ED treatment in patients with placenta previa should be directed at the hemodynamic stability of the patient. The primary therapeutic agents should be intravenous crystalloids and/or transfusions.

Recent studies are now using prothrombin complex and recombinant factor VII to control hemorrhage associated with obstetric complications and placenta previa.

Corticosteroids

Steroids may be administered after consultation with a gynecologist, if vaginal bleeding is mild and intermittent, if the patient is not in labor, and if gestation is less than 37 weeks.

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