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.

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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.

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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.

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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.

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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.

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

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

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• 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.

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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:

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• 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.​

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• Placenta accreta in previous pregnancy: women​ 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.

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• 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

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• Advanced maternal age

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• In vitro fertilization

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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.