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)
Placenta percreta (penetration of chorionic villi into or through the uterine serosa)
All three 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 Placenta Previa Placenta previa is implantation of the placenta over or near the internal os of the cervix. Typically, painless vaginal bleeding with bright red blood occurs after 20 weeks gestation. Diagnosis... read more and have had a cesarean delivery in a previous pregnancy
Incidence of placenta accreta has been increasing; it occurred in about
1/30,000 in the 1950s
1/500 to 2000 in the 1980s and 1990s
3/1000 by the 2000s
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:
Maternal age > 35
Multiparity (risk increases as parity increases)
Submucosal fibroids
Prior uterine surgery, including myomectomy
Endometrial lesions such as Asherman syndrome
Etiology reference
1. Mogos MF, Salemi JL, Ashley M, et al: Recent trends in placenta accreta in the United States and its impact on maternal–fetal morbidity and healthcare-associated costs, 1998–2011. J Matern Fetal Neonatal Med 29 (7):1077–1082, 2016, 2016. doi: 10.3109/14767058.2015.1034103
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 may not be delivered within 30 minutes 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 weeks gestation. If B-mode (gray-scale) ultrasonography is inconclusive, MRI or Doppler flow studies may help.
During delivery, placenta accreta is suspected if
The placenta has not been delivered within 30 minutes 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
If placenta accreta is suspected, clinicians should consider referring the woman to a center with expertise in managing this disorder.
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.
Key Points
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.
Consider referral to a center with expertise in managing placenta accreta.
