Summary
Placenta accreta spectrum is a disorder of placental development in which chorionic villi abnormally attach to or invade the uterine myometrium, preventing normal placental separation after birth. It is classified as placenta accreta, increta, or percreta depending on the depth of myometrial invasion. The exact pathogenesis is unknown, but it is thought to be caused by decidual deficiency (usually at the site of prior uterine scarring) and excessive trophoblastic invasion. Major risk factors include previous cesarean delivery and placenta previa. Although placenta accreta spectrum is often asymptomatic until delivery, it can manifest with a prolonged third stage of labor and severe postpartum hemorrhage (PPH), especially during attempted manual removal of the placenta. Diagnosis is typically made during prenatal ultrasound screening, which may show findings such as loss of the retroplacental clear zone, myometrial thinning, and increased vascularity on color Doppler. A clinical diagnosis made at delivery if the placenta is retained or cannot be removed manually. A cesarean hysterectomy with the placenta left in situ is the standard treatment. Conservative management is only considered for selected patients with a strong desire for fertility-sparing approaches, as the failure rates are high. Placenta accreta spectrum and its treatment have high rates of complications, including life-threatening hemorrhage, and patients require multidisciplinary care and counseling.
Epidemiology
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Incidence [1][2]
- ∼ 0.17% of all pregnancies
- Higher in individuals with previous cesarean delivery
Epidemiological data refers to the US, unless otherwise specified.
Classification
Classification depends on the depth of trophoblast invasion into the uterine wall: [1][3]
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Placenta accreta (FIGO grade 1): most common
- Chorionic villi attach to the myometrium; rather than the decidua basalis; no myometrial penetration
- Adherent placenta: The plane of separation between the placenta and myometrium is not clearly defined.
-
Placenta increta (FIGO grade 2)
- Chorionic villi invade or penetrate the myometrium.
- Macroscopic abnormalities of the placenta (e.g., hypervascularity, bulge)
- Uterus pulls inwards on gentle traction of the cord (dimple sign).
-
Placenta percreta (FIGO grade 3): least common
- Chorionic villi penetrate the myometrium, the serosa, and in some cases, adjacent organs or structures, such as the bladder.
- Placenta is visible through the uterine surface due to the thinned-out myometrium.
The types of abnormal placental attachment: Placenta Accreta “Attaches” to the myometrium, placenta Increta “Invades” the myometrium, and placenta Percreta “Perforates” the myometrium.
Etiology
Pathophysiology [3][4]
- A disorder of placental development that causes abnormal uterine attachment, leading to insufficient placental separation during labor
- The exact underlying pathogenesis is unknown.
- Thought to be caused by a combination of:
- Decidual deficiency: complete or partial lack of decidua in an area of previous scarring within the endometrial-myometrial interface
- Excessive trophoblastic invasion: abnormal growth → uncontrolled invasion of villi through the myometrium, including its vascular system
Risk factors [1][2][4]
Risk factors include prior damage to the endometrium or scarring at the endometrial-myometrial interface.
- Prior cesarean delivery
- Placenta previa
- History of uterine surgery (e.g., endometrial ablation, hysteroscopic removal of intrauterine adhesions, dilatation, curettage)
- Other structural uterine abnormalities (e.g., fibroids, adenomyosis, bicornuate uterus)
- Multiparity
- Advanced maternal age
- Use of assisted reproductive technology
- Asherman syndrome
Placenta previa in a patient with a previous cesarean delivery is the most significant risk factor for placenta accreta spectrum. [1][2][5]
Clinical features
Placenta accreta spectrum is often asymptomatic until delivery. [2][5]
-
Common clinical manifestations (when symptomatic)
-
Prolonged third stage of labor with retained placenta
- Postpartum hemorrhage usually at the time of a failed attempt at manual removal of the placenta
- The cleavage place between the placenta and myometrium is not palpable. [6]
- Antepartum hemorrhage
-
Prolonged third stage of labor with retained placenta
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Other manifestations
- Fever
- Rarely, hematuria in placenta percreta [7]
Placenta accreta spectrum can cause PPH even when the uterus is firm and well-contracted on examination, which distinguishes it from uterine atony, another common cause of retained placenta.
Diagnosis
General principles [2][5]
- Placenta accreta spectrum is typically diagnosed during prenatal ultrasound screening in asymptomatic individuals.
- MRI can be performed if ultrasound is inconclusive.
- In patients without prenatal screening, a clinical diagnosis can be made during delivery if either of the following are present: [8]
- Clinical features of retained placenta (e.g., prolonged third stage of labor)
- Manual placenta removal is not possible (e.g., during the management of PPH or cesarean delivery).
During prenatal screening, periodically evaluate the site of placental implantation in individuals with a previous cesarean delivery. [1][2][5]
Ultrasound [2][5]
- Supportive findings
-
Color Doppler findings
- Turbulent blood flow
- Increased vascularity within and between the placenta, myometrium, and bladder wall
-
Findings specific to placenta increta and percreta [9]
- Increased number of placental vessels extending beyond the myometrium
- Placental tissue extending through the uterine serosa into adjacent organs
Maintain a high index of suspicion for placenta accreta spectrum in individuals with risk factors, even if prenatal ultrasound is normal, and refer to specialists for high-risk pregnancy management. [5]
Differential diagnoses
- Other causes of retained placenta (e.g., uterine atony)
- Other common causes of primary PPH (e.g., bleeding obstetric injuries)
The differential diagnoses listed here are not exhaustive.
Management
Prenatal management [5][8][10][11]
The main focus is to prevent bleeding, which requires high-risk pregnancy management in consultation with multidisciplinary specialists and includes:
- Counseling on the risks and consideration of induced abortion if diagnosed in the previable stage [5]
- Scheduled delivery with optimal definitive treatment [5][10]
- Consideration of pelvic rest based on individual risk (e.g., after a bleeding event to prevent recurrence)
- Preoperative planning for PPH
Management of active bleeding [5][8][10][11]
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Antepartum
- Begin management of antepartum hemorrhage.
- Consult OB/GYN and maternal fetal medicine.
-
Postpartum
- Begin initial management of PPH.
- Expedite urgent definitive treatment by an obstetrician.
- Consult neonatology.
Implement active management of the third stage of labor to minimize the risk of PPH.
In patients with antepartum hemorrhage, avoid digital pelvic examination until placenta previa has been ruled out. [12]
Definitive treatment [5][8][10][11]
Optimal management involves shared decision-making and multidisciplinary consultation.
-
Cesarean hysterectomy
- The standard method of delivery and treatment for placenta accreta spectrum
- The placenta is left in place after delivery, and a complete hysterectomy is performed.
-
Conservative fertility-sparing options: only for selected patients at centers of excellence
- Expectant management
- Gentle manual placental removal
- Conservative surgical techniques
Conservative management of placenta accreta spectrum has a significantly higher risk for short-term complications (e.g., life-threatening hemorrhage) than cesarean hysterectomy. [5]
Prognosis
- Placenta accreta spectrum and its treatment have a high risk of complications, such as hemorrhage, surgical complications, infertility, PTSD, postpartum depression, and death. [1][5]
- Placenta percreta has the highest complication rate. [5]
Given the poor prognosis, ensure multidisciplinary care is available for pre- and post-treatment counseling in patients with placenta accreta spectrum. [1][5]