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| AuthorRobert Resnik, MD | Section EditorsCharles J Lockwood, MDDeborah Levine, MD | Deputy EditorVanessa A Barss, MD |
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INTRODUCTION
Placenta accreta refers to an abnormal placental implantation in which the anchoring placental villi attach to the myometrium, rather than being contained by decidual cells. This results in a placenta that is abnormally adherent to the uterus. Related, but more severe abnormalities of placental implantation include:
INCIDENCE
The incidence of placenta accreta ranged from 1 in 533 to 1 in 2510 deliveries in the United States during the 1980s and 1990s [1,2]. By comparison, placenta accreta was a rare occurrence in 1950, occurring in 1 in 30,000 deliveries [1,3]. The marked increase in incidence has been attributed to the increased prevalence of cesarean delivery in recent years (see 'Risk factors' below).
Combined results from two series involving a total of 138 histologically confirmed, abnormally implanted placentas from hysterectomy specimens showed that 79 percent were accretas, 14 percent were incretas, and 7 percent were percretas [1,2].
RISK FACTORS
The most important risk factor for placenta accreta is previous uterine surgery and the most common setting is placenta previa after a prior pregnancy delivered by cesarean. The mechanism for the abnormal implantation is thought to be thin, poorly formed, or absent decidua basalis in the scarred area of the lower uterine segment that does not resist deep penetration by trophoblast. However, other pathophysiologic processes may be involved. (See "Cesarean delivery: Technique".)
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