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7/1/2011

Management of Placenta Accreta Spectrum Diagnosed at 20 Weeks

Author: Roger Smith, MD

Editor: Elizabeth Ferris-Rowe, MD

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The degree of invasion of the myometrium by the chorionic villi defines placenta accreta (adherent to the myometrium), increta (invading the myometrium) and percreta (perforating through the myometrium).  A 2016 study showed the overall rate in the United States was 1/277, and is likely due to increased cesarean delivery rates.

Placenta accreta spectrum arises when there is abnormal decidua formation at the time of placental implantation, specifically imperfect development of the fibrinoid (Nitabuch’s) layer. This failure is more common when the placenta implants at an abnormal site. The most common risk factor is prior cesarean delivery, with an increasing risk based on number of prior cesarean deliveries. Other risk factors include 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, previous uterine curettage, 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 placenta accreta spectrum, though, and clinical risk factors are equally 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.

In the absence of planned preterm delivery, most patients go to term with normal fetal development. 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 may be attempted in patients strongly desiring to retain fertility, although complications including delayed hemorrhage requiring hysterectomy are common.

Any time the diagnosis is considered, preparations for hysterectomy, including anesthesia, instruments, and adequate blood, should be ready before any attempt is made to free the placenta. If the diagnosis is suspected sufficiently far in advance, the possibility of pregnancy termination should be discussed, although there are currently no data to support the magnitude of risk reduction. When termination is not selected, 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 capabilities of current care site and plans for autologous blood donation and elective cesarean hysterectomy may be made. 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:

American College of Obstetricians and Gynecologists Committee on Practice Bulletins-Obstetrics; Practice Bulletin No. 183: Postpartum Hemorrhage. Obstet Gynecol. 2017 Oct;130(4):e168-e186. doi: 10.1097/AOG.0000000000002351.

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.

Silver RM.  Abnormal Placentation: Placenta Previa, Vasa Previa, and Placenta Accreta. Obstet Gynecol. 2015 Sep;126(3):654-68. doi: 10.1097/AOG.0000000000001005.

Initial Approval July 2011. Reviewed January 2017. Revised and renamed November 2019

 

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