In placenta accreta, the placental villi are not contained by uterine decidual cells, as occurs normally, but extend to the myometrium.
Related abnormalities include
All three abnormalities cause similar problems.
The main risk factor for placenta accreta is
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 by the 2000s; it remains in the range of about 2/1000. In women who have placenta previa, the risk of placenta accreta 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:
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 weeks gestation. If B-mode (gray-scale) ultrasonography is inconclusive, MRI or Doppler flow studies may help.
During delivery, placenta accreta is suspected if
When placenta accreta is suspected, laparotomy with preparation for large-volume hemorrhage is required.
Preparation for delivery is best. Usually, unless the woman objects, cesarean hysterectomy is done at 34 weeks; this approach tends to result in the best balance of maternal and fetal outcomes.
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, but only if acute hemorrhage is absent. For example, the uterus can be left in place, and a high dose of methotrexate can be given to dissolve the placenta; this procedure is done only in certain centers. Uterine artery embolization, arterial ligation, and balloon tamponade are also sometimes used.
In the US, placenta accreta 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 years of age 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 minutes 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 at 34 weeks, unless the woman objects.