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Placenta Previa

By

Antonette T. Dulay

, MD, Main Line Health System

Reviewed/Revised Oct 2022
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Topic Resources

Placenta previa is implantation of the placenta over or near the internal os of the cervix. It typically manifests as painless vaginal bleeding after 20 weeks gestation; the source of bleeding in placenta previa is maternal. Diagnosis is by ultrasonography. Treatment is modified activity if minor vaginal bleeding occurs before 36 weeks gestation, with cesarean delivery at 36 to 37 weeks/6 days. If bleeding is severe or refractory or if fetal status is nonreassuring, immediate cesarean delivery is indicated.

Placenta previa refers to placental tissue that covers any portion of the internal cervical os. A placenta is termed low lying when the placental edge does not cover the internal os but is within 2 cm of it.

Incidence of placenta previa is approximately 5/1000 deliveries (1 General reference Placenta previa is implantation of the placenta over or near the internal os of the cervix. It typically manifests as painless vaginal bleeding after 20 weeks gestation; the source of bleeding... read more ). If placenta previa occurs during early pregnancy, it usually resolves by 28 weeks as the uterus enlarges.

Overview of Placenta Previa
VIDEO

Risk factors

Risk factors for placenta previa include the following:

  • Multiparity

  • Prior cesarean delivery

  • Uterine abnormalities that inhibit normal implantation (eg, fibroids, prior curettage)

  • Prior uterine surgery (eg, myomectomy) or procedure (eg, multiple dilation and curettage [D and C] procedures)

  • Smoking

  • Multifetal pregnancy

  • Older maternal age

Complications

In women who have had a prior cesarean delivery, placenta previa increases the risk of placenta accreta Placenta Accreta Placenta accreta is an abnormally adherent placenta, resulting in delayed delivery of the placenta. Placental function is normal, but trophoblastic invasion extends beyond the normal boundary... read more ; risk increases significantly as the number of prior cesarean deliveries increases (from about 6 to 10% for one cesarean delivery to > 60% for > 4).

General reference

Symptoms and Signs of Placenta Previa

Symptoms of placenta previa usually begin after 20 weeks gestation. It typically manifests as sudden, painless vaginal bleeding; bleeding may be heavy, sometimes resulting in hemorrhagic shock. In some patients, uterine contractions accompany bleeding. The source of bleeding in placenta previa is maternal.

Diagnosis of Placenta Previa

  • Transvaginal ultrasonography

Placenta previa is considered in all women with vaginal bleeding after 20 weeks. If placenta previa is present, pelvic examination, particularly digital cervical examination, may increase bleeding, sometimes causing sudden, massive bleeding; thus, if vaginal bleeding occurs after 20 weeks, pelvic examination is contraindicated unless placenta previa is first ruled out by ultrasonography.

Although placenta previa is more likely to cause painless bleeding than placental abruption Placental Abruption (Abruptio Placentae) Placental abruption (abruptio placentae) is premature separation of the placenta from the uterus, usually after 20 weeks gestation. It can be an obstetric emergency. Manifestations may include... read more , clinical differentiation is still not possible. Thus, ultrasonography is frequently needed to distinguish the two. Transvaginal ultrasonography is an accurate, safe way to diagnose placenta previa.

Pearls & Pitfalls

  • If vaginal bleeding occurs after 20 weeks gestation, exclude placenta previa by ultrasonography before doing a pelvic examination.

In all women with suspected symptomatic placenta previa, fetal heart rate monitoring is indicated.

Treatment of Placenta Previa

  • Hospitalization and modified activity for a first episode of bleeding before 36 weeks

  • Delivery if mother or fetus is unstable

  • If the woman is stable, cesarean delivery at 36 weeks/0 days to 37 weeks/6 days

For a first (sentinel) episode of vaginal bleeding before 36 weeks, management consists of hospitalization, modified activity (modified rest), and avoidance of sexual activity, which can cause bleeding by initiating contractions or causing direct trauma to the placenta. Modified activity involves refraining from any activity that increases intra-abdominal pressure for a long period of time—eg, women should stay off their feet most of the day. If bleeding stops, ambulation and usually hospital discharge are allowed.

Typically for a 2nd bleeding episode, patients are readmitted and may be kept for observation until delivery.

Some experts recommend giving corticosteroids to accelerate fetal lung maturity when early delivery may become necessary and gestational age is < 34 weeks. Corticosteroids may be used if bleeding occurs after 34 weeks and before 36 weeks (late preterm period) in patients who have not been given corticosteroids before 34 weeks (1 Treatment references Placenta previa is implantation of the placenta over or near the internal os of the cervix. It typically manifests as painless vaginal bleeding after 20 weeks gestation; the source of bleeding... read more ).

Timing of delivery depends on the maternal and/or fetal condition. If the patient is stable, delivery can be done at 36 weeks/0 days to 37 weeks/6 days. Documentation of lung maturity is necessary (2 Treatment references Placenta previa is implantation of the placenta over or near the internal os of the cervix. It typically manifests as painless vaginal bleeding after 20 weeks gestation; the source of bleeding... read more ).

Delivery is indicated for any of the following:

  • Heavy or uncontrolled bleeding

  • Nonreassuring results of fetal heart monitoring

  • Maternal hemodynamic instability

Delivery is cesarean for placenta previa. Vaginal delivery may be possible for women with a low-lying placenta if the placental edge is within 1.5 to 2.0 cm of the cervical os and the clinician is comfortable with this method.

Treatment references

Key Points

  • Placenta previa is implantation of the placenta over or near the internal os of the cervix.

  • Placenta previa typically manifests as painless vaginal bleeding after 20 weeks gestation, and placental abruption is usually associated with uterine pain and tenderness; however, clinical differentiation is often not possible.

  • Consider placenta previa in all women who have vaginal bleeding after 20 weeks.

  • For most first bleeding episodes before 36 weeks, recommend hospitalization, modified activity, and abstinence from sexual activity.

  • Consider corticosteroids to accelerate fetal lung maturity if delivery may be required before 34 weeks or if bleeding occurs between 34 and 36 weeks in patients who have not been given corticosteroids before 34 weeks.

  • Cesarean; delivery is indicated when the mother or fetus is unstable or, if mother and fetus are stable, at 36 weeks/0 days to 37 weeks/6 days.

Drugs Mentioned In This Article

Drug Name Select Trade
Adbeon, Alphatrex, Beta 1 Kit, Beta Derm , Betanate , Betatrex, Beta-Val, BSP 0820, Celestone, Del-Beta , Diprolene, Diprolene AF, Diprosone, Luxiq Foam, Maxivate, ReadySharp Betamethasone, Sernivo, Valisone
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