Placental Accretion

What is placental accreta?

Placental accreta is the invasion at different depths of the myometrium by trophoblast that can cause abnormal adhesion. Its incidence increases when there is a placenta previa due to the structure found in the cervix as described in the article of Placenta Previa, or when implanted over a scar from a previous uterine incision or perforation.

The etymology of acretism comes from Latin ac + crescere: to grow from adhesion or coalescence. This abnormal implantation of the placenta is secondary to the partial or total absence of the basal decidua and the imperfect development of the fibrinoid or Nitabuch layer.

What is the incidence of placental accreta?

The incidence of placental accretacy according to the American College of Obstetricians and Gynecologists ACOG is 1 case per 533 births, this has shown that this disease has increased since 1980 where the incidence was of 1 case in every 2,500 deliveries, which informs us that it has increased in frequency. These latest data should alert doctors since pregnant women with placenta accreta, increta or percreta now have a higher morbidity and maternal mortality. In a 2010 review, it reports that of 10,000 maternal deaths in the United States, 8% were due to postpartum hemorrhage secondary to the accretion syndrome.

What is the pathophysiology of placental accreta?

During a normal pregnancy the implantation of the placenta, at a miscroscopic level, it is observed that the placental villi are attached to the decidual cells, but when a pregnant woman presents placental accreta, a junction between these placental villi and the fibers is observed in the histological study. muscles of the uterus, the latter prevents normal placental separation after delivery.

This can be due to a defect in the constitutional endometrium that can be generated by previous traumas such as cesarean, curettage, placenta previa among others.

It must be borne in mind that placental accreta is not only caused by the deficiency of the anatomical layer, but it has also been seen that cytotrophoblasts can control decidual invasion through angiogenesis factors.

How is placental accreta classified?

There are 3 types of placental accreta that differ depending on the depth of invasion of the trophoblast in the uterus.

Placenta Acreta

This is a type of adherence of the placenta that is characterized by the villi are attached to the myometrium, this is presented in 80%, being the most frequent of the three.

Placenta Increta

Here the villi of the placenta already invade the myometrium, as seen in the image, this type of placenta is presented in 15%.

Placenta Percreta

In this type of placental accretion, the villi have penetrated the entire thickness of the wall of the uterus, reaching the serosa and generating the greatest complications of this disease. The placenta percreta is present in 5%, being the least frequent of the three types of placental accreta.

Clasificación del acretismo placentario
Classification of placental accreta. Image taken from the book: Williams Obstetrics 24 ed

Abnormal adherence in these three variables can be divided into 2 types: Total accreta placenta that is when there is adherence of all focal lobules and placenta accreta that describe it when a single lobe or part of the lobe of the placenta adheres.

What are the risk factors of placental accreta?

The most important risk factors of pregnant women to present this disease are: Having presented low implantation of the placenta (placenta previa or marginal placenta), having a history of cesarean section, if it presents the two antecedents, is more likely to present the accreta.

Other risk factors are:

  • Myomectomy
  • Curettage
  • Surgical procedures that generate the loss of the basal decidua by scar.

Signs and symptoms of placental accreta

First and second trimesters

The clinic of patients who are in the periods of pregnancy usually there is bleeding as a consequence of the co-existing placenta previa. When the patient does not have vaginal bleeding, her diagnosis is delayed until the third trimester, which by means of ultrasonography (ultrasound) an adherence of the placenta is observed.

How is placental accreta diagnosed?

In order to make the diagnosis of this disease, it is mainly done through transvaginal ultrasound where the infiltration of the placenta in the myometrium can be observed.

The sensitivity of transvaginal ultrasound in placental accreta is between 77 and 87% with a specificity of 96 to 98%, with a positive and negative predictive value of 65 – 98%

Another test that can also be performed is color Doppler that has a high predictive value of myometrial invasion. It can be suspected if the distance between the serous wall and the uterine bladder has retroplacental vessels <1mm and if there are large intraplacental gaps.

For MRI Magnetic Resonance diagnosis, it should be taken into account that it is a complementary examination of transvaginal ultrasound, which should be performed only to identify the anatomy, the degree of invasion and possible ureteral or bladder involvement.

Which is the treatment?

The treatment of acretism is through surgery scheduled after 36 weeks, the treatment must be performed by an obstetrician gynecologist who will define the appropriate management (surgical technique, time of the procedure), and if it can be conservative ( maintain fertility of the woman) or radical (hysterectomy) because it can generate serious adverse consequences such as postpartum hemorrhage.


  1. Cunningham FG, Leveno KJ, Bloom SL, Spong CY, Dashe JS, Hoffman BL, et al. Obstetrical Hemorrhage. Williams Obstetrics, 24e. New York, NY: McGraw-Hill Education; 2013.