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7/1/2011

Management of Placenta Accreta Spectrum Diagnosed Antenatally

Placenta accreta spectrum (PAS) encompasses a number of diagnoses describing the failure of the placenta to detach from the myometrium at the time of delivery. Historically, the degree of invasion of the myometrium by the chorionic villi defined the ultimate diagnosis asplacenta accreta (adherent to the myometrium), increta (invading the myometrium) or percreta (perforating through the myometrium) however there are newer grading schemas which take into account clinical or pathologic findings to classify the adherent placenta.  Recent estimates show the incidence of PAS as affecting 1/588 pregnancies and this is likely increasing secondary to increased cesarean delivery rates.

The exact etiology of PAS disorders is not fully understood. Traditionally, PAS was thought to arise from abnormal trophoblastic invasion at the time of placental implantation, specifically imperfect development of the fibrinoid (Nitabuch’s) layer. New models of PAS suggest that an abnormal uterine wall may be a major factor in the development of PAS.This failure is more common when the placenta implants at an abnormal site. The most significant risk factor for PAS is a placenta previa diagnosed in  a patient with a history of cesarean delivery. Other risk factors include prior cesarean delivery, with an increasing risk based on number of prior cesarean deliveries, placenta previa (5% without previous uterine surgery, 15%–70% with previous surgery), multigravidity (1 of 500,000 for parity <3, 1 of 2500 for parity >6), older age, IVF, previous uterine curettage or myomectomy, previous endomyometritis, manual removal of the placenta, leiomyomata, uterine malformation, prior abortion, and endometrial ablation.

Placenta accreta is suspected on ultrasonography when there is placenta previa, loss or blurring of the normal placenta-uterine wall boundary, the absence of the subplacental hypoechoic zone, or the presence of lacunar blood flow patterns.  The finding of placenta previa on ultrasound is present in more than 80% of accretas. MRI may occasionally be helpful to delineate invasion into adjacent structures but is not necessary to make the diagnosis antepartum. The absence of ultrasound findings does not preclude PAS, though, and clinical risk factors are the most important predictors. The final diagnosis is established histologically by the absence of the decidua basalis (replaced by loose connective tissue). The decidua parietalis may be normal or absent. The villi may be separated from the myometrial cells by a layer of fibrin.

 When placenta accreta spectrum is diagnosed at delivery, life-threatening hemorrhage may occur; maternal mortality of 2%–6% has been reported for treatment by hysterectomy and up to 30% for conservative management. Rupture of the uterus or inversion may occur during attempts to remove the placenta. Most patients require hysterectomy. Aggressive fluid and blood support, including use of massive transfusion protocols, must be provided as necessary. Coagulopathy secondary to blood loss and replacement is common. If the placenta can be delivered, oxytocin or other uterotonic agents are used to promote uterine contractions. If invasion of the myometrium is incomplete and the bladder is spared, conservative management by uterine packing or partial resection and reconstruction may be attempted in patients strongly desiring to retain fertility, although complications including delayed hemorrhage requiring hysterectomy are common.

Any time the diagnosis is suspected transfer of the patient to a PAS center is recommended. If unavailable or not feasible then a multidisciplinary team should be assembled and preparations for hysterectomy, including anesthesia, instruments, and adequate blood, should be ready before delivery. If the diagnosis is suspected sufficiently far in advance discussions with the patient should include the timing of delivery and transfer of care to a facility with maternal level III or higher care. Depending on the capabilities of the current care site, plans for autologous blood donation and elective cesarean hysterectomy may be appropriate. Combined maternal and fetal outcomes are optimized with planned delivery at 34 0/7 – 35 6/7 weeks, although delivery timing may be individualized based on the clinical situation.

Further Reading:

Committee on Practice Bulletins-Obstetrics. Practice Bulletin No. 183: Postpartum Hemorrhage. Obstet Gynecol. 2017 Oct;130(4):e168-e186. doi: 10.1097/AOG.0000000000002351. PMID: 28937571.

American College of Obstetricians and Gynecologists, Society for Maternal Fetal Medicine, Obstetric Care Consensus No. 7: Placenta Accreta Spectrum. Obstet Gynecol. 2018 Dec;132(6):e259-e275. doi: 10.1097/AOG.0000000000002983.

Einerson BD, Gilner JB, Zuckerwise LC. Placenta Accreta Spectrum. Obstet Gynecol. 2023 Jul 1;142(1):31-50. doi: 10.1097/AOG.0000000000005229. Epub 2023 Jun 7. PMID: 37290094; PMCID: PMC10491415.

Initial Approval July 2011. Reviewed January 2017. Revised and renamed November 2019. Minor Revision July 2021. Revised March 2023. Minor Revision November 2024.

Originally titled “Management of Placenta Accreta Spectrum Diagnosed at 20 Weeks”.  Retitled July 2021. 

 

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