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 between the endometrium and myometrium (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 cesarean hysterectomy.
In placenta accreta, the placental villi are not contained by uterine decidual cells, as occurs normally, but attach to the myometrium.
Placenta accreta spectrum includes 2 additional subtypes (1):
Placenta increta: Invasion of chorionic villi into the myometrium
Placenta percreta: Penetration of chorionic villi into or through the uterine serosa
All three subtypes cause similar complications.
General reference
1. American College of Obstetricians and Gynecologists; Society for Maternal-Fetal Medicine: Obstetric Care Consensus No. 7: Placenta Accreta Spectrum. Obstet Gynecol 132(6):e259-e275, 2018. doi:10.1097/AOG.0000000000002983
Etiology of Placenta Accreta
The main risk factor for placenta accreta is
Prior cesarean delivery
In the United States, rates of cesarean delivery have increased, and incidence of placenta accreta has also been increasing. One large study of hospital discharges reported an incidence of placenta accreta of 1 in 2510 deliveries in the 1970s, 1 in 4027 in the 1980s, and 1 in 533 from 1982 to 2002 (1). A clinical database study reported an incidence of placenta accreta in 1 in 272 deliveries from 1998 to 2011 (2).
Placenta accreta spectrum most commonly occurs in women who have placenta previa in the current pregnancy and have had a prior cesarean delivery. In pregnancies with placenta previa, placenta accreta spectrum risk increases with number of prior cesarean deliveries (3):
No prior cesarean delivery – 3%
1 prior cesarean delivery – 11%
2 prior cesarean deliveries – 40%
3 prior cesarean deliveries – 61%
4 prior cesarean deliveries – 67%
Other risk factors include the following:
Maternal age > 35
Multiparity (risk increases as parity increases)
Submucosal fibroids
Prior uterine surgery other than cesarean, including myomectomy
Endometrial lesions, such as Asherman syndrome
Etiology references
1. Wu S, Kocherginsky M, Hibbard JU: Abnormal placentation: twenty-year analysis. Am J Obstet Gynecol 192(5):1458-1461, 2005. doi:10.1016/j.ajog.2004.12.074
2. 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
3. Silver RM, Landon MB, Rouse DJ, et al: Maternal morbidity associated with multiple repeat cesarean deliveries. Obstet Gynecol 107(6):1226-1232, 2006. doi:10.1097/01.AOG.0000219750.79480.84
Symptoms and Signs of Placenta Accreta
Bleeding may be minimal or absent, and placenta accreta is often suspected if the placenta is not delivered within 30 minutes after delivery of the fetus. Usually, vaginal bleeding is profuse during manual separation of the placenta after delivery of the fetus.
Diagnosis of Placenta Accreta
Ultrasonography for women at risk
Thorough evaluation of the uteroplacental interface by ultrasonography (transvaginal or transabdominal) is warranted in women at risk; a consensus on definition of markers has been published. If there is diagnostic uncertainty, ultrasonography can be repeated periodically, beginning at 20 to 24 weeks gestation (1). 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.
Diagnosis reference
1. Shainker SA, Coleman B, Timor-Tritsch IE, et al: Special Report of the Society for Maternal-Fetal Medicine Placenta Accreta Spectrum Ultrasound Marker Task Force: Consensus on definition of markers and approach to the ultrasound examination in pregnancies at risk for placenta accreta spectrum [published correction appears in Am J Obstet Gynecol 2021 Jul;225(1):91]. Am J Obstet Gynecol 224(1):B2-B14, 2021. doi:10.1016/j.ajog.2020.09.001
Treatment of Placenta Accreta
Cesarean hysterectomy
If placenta accreta is suspected, clinicians should consider referring the woman to a center with pelvic surgeons experienced with cesarean hysterectomy.
If there is a high suspicion of placenta accreta, scheduled cesarean delivery is the best treatment option. Usually, cesarean hysterectomy is done at 34 to 35 6/7 weeks gestation; this approach tends to result in the best balance of maternal and fetal outcomes.
If cesarean hysterectomy is performed, 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.
Key Points
In the United States, 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 to 35 6/7 weeks, unless the woman objects.
Consider referral to a center with expertise in managing placenta accreta.
