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Pregnant Woman
Placenta Accreta
Jovian Wat, PhD

Placenta accreta is a condition of pregnancy where the placenta attaches to the uterus in an abnormally deep manner. In normal delivery, the placenta detaches from the uterus after the delivery of the baby. In women with placenta accreta, the placenta fails to detach from the wall of the uterus, increasing the risk of bleeding complications at delivery.


Read below to learn more about placenta accreta.

Normal endometrial function


During the course of the menstrual cycle, the inner lining of the uterus (called the endometrium) prepares for pregnancy. If conception does not occur, the endometrial lining is shed as menstrual flow, and the menstrual cycle restarts.

If conception does occur, the fertilized egg attaches to the endometrial lining. This attachment stimulates the endometrium to form an area with lots of blood vessels and high levels of blood flow, known as the decidua. The decidua is the zone between the embryo and the uterus.

Following the attachment of the fertilized egg, placental cells that come from the egg anchor to the decidua. This anchoring holds the placenta and the embryo in the uterus. Blood from the mother flows to the decidua to supply the placenta and fetal growth throughout pregnancy.

In normal pregnancy, the baby is delivered before the placenta. Contractions of the uterus then slowly cause the placenta to detach from the decidua and endometrium. After the placenta is detached and delivered from the mother, the uterus contracts and becomes firm. This action compresses the blood vessels of the uterus to prevent excessive bleeding.

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What is placenta accreta?


Placenta accreta is a condition of pregnancy where the placenta attaches to the uterus in an abnormally deep manner. The placental cells that usually anchor the placenta to the decidua deeply invade the uterus and form an overly strong attachment.


Placenta accreta is a rare disease, occurring in less than 1% of pregnant women; however, rates of placenta accreta are increasing.


There are three grades of invasiveness, in order of severity:


  • Placenta accreta - placental cells invade past the decidua and anchor deeply into the endometrial layer of the uterus

  • Placenta increta - placental cells invade past the endometrium layer and into the muscular layer of the uterus, known                               as the myometrium

  • Placenta percreta - placental cells invade past the muscular layer of the uterus and into the outermost serosa layer                                   of the uterus


An abnormally strong attachment of the placenta to the uterus prevents the placenta from detaching during delivery. This attachment prevents the uterus from contracting and compressing the uterine blood vessels, increasing the risk of uncontrolled vaginal bleeding or hemorrhage.


Up to 60% of placenta accreta patients suffer significant health complications, including major blood loss requiring transfusion and intensive care hospitalization, while 1 in 15 women with placenta accreta die from the complications.

Risk factors for placenta accreta


There are a number of known risk factors that can increase the chances of developing placenta accreta. Increasing rates of placenta accreta is thought to be due to increasing rates of the following risk factors:

  • History of Caesarean sections or uterine surgery: previous surgeries or infections that involved the uterus can cause scarring and damage to the uterus. If the placenta in the current pregnancy forms over a previous scar or area of endometrial damage, placental cells are more likely to invade past the decidua. Women with 5 or more cesarean deliveries are at a 7% risk of developing placenta accreta.​

  • Placenta accreta in previous pregnancywomen​ with a history of placenta accreta are at higher risk in future pregnancies. Studies have shown that over 10% of women with placenta accreta will develop the condition again.

  • Placenta previa: placenta previa is a condition where the placenta attaches low in the uterus and covers at least part of the cervical opening. The majority of women with placenta accreta also have placenta previa.


  • Numerous previous pregnancies

  • Advanced maternal age

Symptoms of placenta accreta


Most pregnant women with placenta accreta do not have any symptoms of this condition. Some women with placenta accreta experience some bleeding during pregnancy.

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Testing & investigations for placenta accreta

Placenta accreta is not always detected in routine clinical tests for pregnant women. However, since delivery in women with placenta accreta is more complicated and commonly involves surgery, early identification and diagnosis of placenta accreta are important to help doctors properly prepare for delivery and counsel the patient regarding potential health outcomes. Pregnant women who have placenta accreta diagnosed during pregnancy are at lower risk of bleeding complications, when compared to pregnant women who had placenta accreta diagnosed at the time of delivery.

Medical imaging can detect signs of placenta accreta, typically in the second or third trimester of pregnancy. Doctors can check for placenta accreta by looking for abnormal blood low patterns or structure in the placenta and uterus of pregnant women. Doctors can also look for evidence of placenta previa through ultrasound imaging, as this condition is common in pregnant women with placenta accreta.


Transabdominal and transvaginal ultrasound may be used to investigate the placenta. Magnetic resonance imaging (MRI) may also be used if available.

Treatment & management of placenta accreta

There is no treatment for placenta accreta, as this is a structural condition that develops at the beginning of pregnancy. 


Placenta accreta is a serious condition that requires management by specialized doctors in a prepared setting. Pregnant women with suspected placenta accreta are advised to deliver at hospitals with higher levels of care that are equipped with the resources to manage potential complications at delivery. The delivery of the baby and removal of placenta in women with placenta accreta is a complicated surgery.

The timing of delivery in women with placenta accreta is important to balance the mom and baby's health. If pregnant women with placenta accreta go into natural labour, the delivery is less controlled and the risk of bleeding can be elevated. Doctors typically prefer to deliver these babies via planned Caesarean delivery between 34 to 36 weeks of pregnancy.

During delivery, women with placenta accreta commonly experience blood loss that requires a blood transfusion. As many as 90% of pregnant women with placenta accreta require blood transfusions at delivery. Depending on the level of placental invasiveness, the uterus may have to be removed through a surgical procedure called a hysterectomy to prevent maternal severe bleeding. Placenta accreta has now become the most common reason for cesarean hysterectomy in developed countries. If extensive surgery is needed, women may require intense monitoring following delivery to monitor for complications, including bleeding.

Prevention of placenta accreta


It is not possible to prevent placenta accreta. Pregnant women who have known risk factors for placenta accreta or have had placenta accreta in a previous pregnancy may be more closely followed by an obstetrician–gynecologist doctor or doctor with experience in placenta accreta in a high-level hospital with appropriate resources transfusions.



Placenta accreta is a serious condition of pregnancy where the placenta attaches deeply to the utertus wall. Pregnant women with placenta accreta are at higher risk of complications, especially increased bleeding during delivery. It is important to identify placenta accreta during pregnancy in order for specialized doctors to prepare for delivery and reduce the risk of complications.


Every woman and every pregnancy is unique. Pregnant women should speak to their healthcare provider to ensure maternal and fetal safety. This article is meant to provide readers with current information and opinions. All medical and treatment decisions should be discussed with your healthcare provider.

This article was written by Dr. Jovian Wat, and edited by Dr. Kelsey McLaughlin and Dr. Melanie Audette.

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