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Placenta Accreta


Key Points

  • Prior CD is the most important factor associated with PA, and the risk of PA increases with the number of prior CDs.

  • Suspected PA on prenatal imaging allows planned management of the condition and has been associated with a reduced rate of maternal morbidity.

  • Ultrasound imaging is superior to MRI for routine screening of PA in at-risk women, but the degree of invasion to adjacent pelvic tissues and organs may be better ascertained with MRI.

  • The optimum time for planned delivery for a woman with suspected PA and placenta previa is approximately 34 weeks, following a course of corticosteroid injections.

  • When a PA is suspected, it is best to avoid disturbing the placenta and to leave it attached at the time of cesarean delivery.

  • The role of interventional radiology at the time of primary caesarean delivery and hysterectomy remains uncertain.

  • A pregnancy following a previous PA that was treated with conservative management is at increased risk for adverse maternal outcomes such as recurrent PA, uterine rupture, PPH, and peripartum hysterectomy.

Overview

  • ▪

    The term placenta increta is used to describe deep myometrial invasion by trophoblast villi; placenta percreta refers to villi perforating through the full thickness of the myometrium and uterine serosa with possible involvement of adjacent organs. The difference between placenta accreta, increta, and percreta is related to the extent of invasion, and the umbrella term disorders of invasive placentation is used to encompass all three ( Fig. 21.1 ).

    Fig. 21.1, Uteroplacental relationships found with invasive placentation.

  • ▪

    When placenta accreta (PA) is present, the failure of the entire placenta to separate normally from the uterine wall after delivery is typically accompanied by severe postpartum hemorrhage.

Pathogenesis

  • ▪

    Total or partial absence of decidua is the characteristic histologic feature of PA and is relatively clear-cut in cases of implantation on a uterine scar. This results in the absence of the normal plane of cleavage above the decidua basalis, thus preventing placental separation after delivery.

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