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Definitions
Placenta accreta: placental implantation in which there is an abnormally firm adherence to the uterine wall.
Placenta increta: abnormal implantation of the placenta that penetrates into the myometrium.
Placenta percreta: abnormal implantation of the placenta that penetrates through the myometrium to the serosa.
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Placenta accreta presents serious clinical problems that can lead to massive blood loss and even death. Torrential bleeding occurs when there is forceful separation of an abnormally implanted placenta from the uterine wall. Placenta accreta and its variations (placenta increta and percreta) account for 33% to 50% of all emergency peripartum hysterectomies.1,2, and 3 The major risk factor, the number of previous cesarean sections, is increasing at a rapid rate; in some hospitals in the United States, cesarean sections have reached over 40% of deliveries. At the University of Chicago, placenta accreta increased 10-fold in the years 1982 to 2002 and was present in 9.3% of women with placenta previa.4
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Because management of placenta accreta requires substantial resources, such as the ability to transfuse large amounts of blood rapidly, it would be advantageous to make the diagnosis accurately before delivery. There are also new methods of prospective management that can markedly reduce blood loss and other morbidity. Considerable progress has been made in the use of ultrasound to predict its presence in all 3 trimesters. The exact role of magnetic resonance imaging (MRI) has not been defined, but it may be important in the future to evaluate patients in whom suspicion has been raised by ultrasound.
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In placenta accreta, part or all of the decidua parietalis between the myometrium and placenta is missing, leaving the trophoblast to lie in direct contact with the myometrium. This lack of decidua means that there is no natural separation plane and the placenta is thus firmly adherent to the myometrium. In placenta increta, there is growth of the trophoblast into the myometrium, and in percreta all the way through it. In placenta percreta, the placenta may also invade the bladder, making removal of the uterus very difficult and often resulting in loss of some of the bladder. Percreta can also involve the broad ligament, cervix, or uterine artery. Usually, this lack of decidua involves only part of the placental myometrial surface, but even a limited area creates a problem if the placenta is forcefully separated from the myometrium. If complete separation of the placenta does not occur, leaving parts attached to the myometrium, the uterus does not contract well: it is uterine contraction that provides hemostasis after delivery.
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Placenta accreta, increta, and percreta are known as placental attachment disorders (PADs). In the following discussion, the term placenta accreta refers to all 3 types of placental attachment disorders. The cause is not known because implantation is under the control of many molecular and cellular mechanisms.5...