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Key Terms

  1. Placenta attachment disorders (PAD): spectrum of disorders of abnormal placental implantation to the uterine wall due to an absence or deficiency of the decidua.

  2. Abnormally invasive placenta (AIP): clinical term to describe a placenta that does not separate spontaneously during delivery and that causes high blood loss if forcefully separated.

  3. Placenta accreta: abnormal adherence of the placenta to the myometrium instead of the uterine decidua.

  4. Placenta increta: abnormal invasion of placental tissue into the myometrium.

  5. Placenta percreta: abnormal placental invasion through the myometrium into the serosa and/or eventually adjacent organs.

  6. Cesarean scar pregnancy (CSP): abnormal implantation of the placenta at the site of the previous cesarean scar.

  7. Early placenta accreta: PAD in the second trimester of pregnancy.


At the end of the 19th century the first microscopic examinations of uterine-placental specimens were conducted, derived from patients, in which the placenta could not be removed during delivery. Histological evidence of an “attached placenta” was brought to light.1 In 1922, Dietrich totally traced 19 cases of placenta accreta in which the diagnosis had been histologically verified.2 He documented that all of these cases were multiparas with history of previous surgical interventions, such as manual removal of the placenta in one or more previous pregnancies, or endometrial ablation.

It was not until the year 1978 when Larsen and Solomon reported the first case of cesarean scar pregnancy (CSP). The first review article by Fylstra summarized a total of 18 cases up to 2002.3,4 Although cesarean scar pregnancy was first considered a different clinical entity, Timor-Tritsch et al showed it to be the histopathological expression of a placental attachment disorder (PAD) in the first trimester.5 Today we use the term “placenta attachment disorders” (PADs) to refer to the whole spectrum of disorders concerning abnormal placental implantation into the uterine wall. Collins et al suggested using “abnormally invasive placenta (AIP)” as the clinical term to describe any placenta that does not separate spontaneously during a delivery and that causes pathological high blood loss if forcefully separated.6

PADs present serious clinical conditions 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. With increasing depths of invasion, morbidity and mortality rate increases.7,8 The term placenta accreta is used if histopathologically the placenta attaches directly to the myometrium, placenta increta if there is deep myometrial invasion, and placenta percreta if the placenta is perforating through the full thickness of the myometrium and uterine serosa with possible involvement of adjacent organs.9 Out of all cases with PAD in the third trimester, 75% are placenta accreta, 18% placenta increta, and 7% placenta percreta.7


Worldwide the incidence of AIP has increased over the past decades. In 1977, Breen et al reported an ...

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