Management of Placenta Accreta Diagnosed at 20 Weeks
7/1/2011 - Roger Smith, MD
Editor: David Chelmow, MD
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).
Placenta accreta and its variants all arise 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. Risk factors for abnormal placentation include placenta previa (5% without previous uterine surgery, 15%–70% with previous surgery), previous cesarean delivery, 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.
When only a small part of the placental disc is involved, the diagnosis may not be made until after delivery, when there is failure of normal separation of the placenta. This is often accompanied by abnormally heavy bleeding after delivery of the placenta. Low-lying placentas noted in studies performed before 30 weeks may “migrate,” leaving the cervix free at term (up to 90% of cases) and the majority of low lying or complete placenta previa patients do not have an abnormality of implantation, only location. Placenta accreta is suspected on ultrasonography when there is 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 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.
Most patients go to term with normal fetal development. 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, discussions with the patient should include the timing of delivery and potential to transfer of care depending on capabilities of current care site, and plans for autologous blood donation and elective cesarean hysterectomy may be made. When placenta accreta 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 possible.
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Silver RM. Abnormal placentation: Placenta previa, vasa previa, and placenta accreta. Obstet Gynecol 2015;126:654-68.
Initial Approval July 2011; Revised June 2015; Updated January 2017
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