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Placenta Accreta

by Julie S. Moldenhauer, MD

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 (called Nitabuch layer). In such cases, manual removal of the placenta, unless scrupulously done, results in massive postpartum hemorrhage. Prenatal diagnosis is by ultrasonography. Treatment is usually with scheduled cesarean hysterectomy.

In placenta accreta, the placental villi are not contained by uterine decidual cells, as occurs normally, but extend to the myometrium. Related abnormalities include placenta increta (invasion of chorionic villi into the myometrium) and placenta percreta (penetration of chorionic villi into or through the uterine serosa). All 3 abnormalities cause similar problems.

Etiology

The main risk factor for placenta accreta is

  • Prior uterine surgery

In the US, placenta accreta most commonly occurs in women who have placenta previa and have had a cesarean delivery in a previous pregnancy. Incidence of placenta accreta has increased from about 1/30,000 in the 1950s, to about 1/500 to 2000 in the 1980s and 1990s, and to 3/1000 in the 2000s. Risk in women who have placenta previa increases from about 10% if they have had one cesarean delivery to > 60% if they have had > 4 cesarean deliveries. For women without placenta previa, having had a previous cesarean delivery increases risk very slightly (< 1% for up to 4 cesarean deliveries).

Other risk factors include the following:

  • Maternal age > 35

  • Multiparity (risk increases as parity increases)

  • Submucosal fibroids

  • Prior uterine surgery, including myomectomy

  • Endometrial lesions such as Asherman syndrome

Symptoms and Signs

Usually, vaginal bleeding is profuse during manual separation of the placenta after delivery of the fetus. However, bleeding may be minimal or absent, but the placenta is not delivered within 30 min after delivery of the fetus.

Diagnosis

  • Ultrasonography for women at risk

Thorough evaluation of the uteroplacental interface by ultrasonography (transvaginal or transabdominal) is warranted in women at risk; it can be done periodically, beginning at 20 to 24 wk gestation. If ultrasonography is inconclusive, MRI or Doppler flow studies may help.

During delivery, the disorder is suspected if

  • The placenta has not been delivered within 30 min of the infant's delivery.

  • Attempts at manual removal cannot create a plane of separation.

  • Placental traction causes large-volume hemorrhage.

When placenta accreta is suspected, laparotomy with preparation for large-volume hemorrhage is required.

Treatment

  • Scheduled cesarean hysterectomy

Preparation for delivery is best. Usually, unless the woman objects, cesarean hysterectomy is done as soon as fetal lung maturity is confirmed (usually at about 35 to 36 wk).

If cesarean hysterectomy is done (preferably by an experienced pelvic surgeon), a fundal incision followed by immediate clamping of the cord after delivery can help minimize blood loss. The placenta is left in situ while hysterectomy is done. Balloon occlusion of the aorta or internal iliac vessels may be done preoperatively but requires a skilled angiographer and may cause serious thromboembolic complications.

Rarely (eg, when placenta accreta is focal, fundal, or posterior), clinicians can attempt to save the uterus; for example, the uterus can be left in place, and a high dose of methotrexate can be given to dissolve the placenta. Uterine artery embolization, arterial ligation, and balloon tamponade are also sometimes used.

Key Points

  • In the US, placenta accreta in the US is becoming increasingly common, occurring most often in women who have placenta previa and have had a cesarean delivery in a previous pregnancy.

  • Consider using periodic ultrasonography to screen women who are > 35 or are multiparous (particularly if placenta previa developed previously or they have had a prior cesarean delivery), who have submucosal fibroids or endometrial lesions, or who have had prior uterine surgery.

  • Suspect placenta accreta if the placenta has not been delivered within 30 min of the infant's delivery, if attempts at manual removal cannot create a plane of separation, or if placental traction causes large-volume hemorrhage.

  • If placenta accreta is diagnosed, do cesarean hysterectomy as soon as fetal lung maturity is confirmed.

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