Placenta accreta is a serious complication of pregnancy in which the placenta attaches to the deeper layers of the uterine wall, the uterine muscle, or organs outside of the uterus such as the bladder or intestines. In these cases it is difficult for the placenta to detach following the birth, which can lead to postpartum hemorrhage.

Placenta accreta is usually detected on prenatal ultrasound and more commonly occurs in people with a history of prior cesarean birth (c-section). Other risk factors for placenta accreta include advanced maternal age, history of uterine curettage, and placenta previa.

It is important that placenta accreta is diagnosed during prenatal care in order to plan for a scheduled c-section with hysterectomy (removal of the uterus) at the time of delivery. Making a plan for delivery can help prevent complications for both the mother and the baby.

Common symptoms

Placenta accreta does not typically cause any symptoms. It is therefore important to engage in regular prenatal care so that this condition can be recognized.

While there are often no signs or symptoms of placenta accreta, some cases will present with vaginal bleeding. This bleeding is typically painless and without any other identifiable cause. It is recommended to seek urgent medical attention for vaginal bleeding in pregnancy in order to identify the cause of the bleeding and initiate appropriate treatment.

Making a diagnosis

The diagnosis of placenta accreta is made on obstetric (prenatal) ultrasound. During an ultrasound the doctor can visualize any abnormalities of the placenta, such as hypervascularity (an increase in blood vessels), in addition to other signs of placenta accreta spectrum such as a thinning out of the uterine muscle (myometrium) or evidence of the placenta growing into the bladder.

Early diagnosis of placenta accreta can decrease the risk for maternal complications.

Ultrasound is considered a very safe procedure for both the pregnant person and the fetus. Pregnancies that are considered to be high risk may involve more frequent and detailed ultrasounds.

In some cases, a doctor may also order an MRI (magnetic resonance imaging) to aid in diagnosis. While the use of MRI in the diagnosis of placenta accreta is controversial, it may be indicated if ultrasound results are inconclusive or uncertain.

Types of placenta previa

Placenta accreta can be classified according to how deeply the placenta is attached to the uterus. The three types are known as:

Placenta accreta: the most common type, in which the placenta invades the decidua, or the inner layer of the uterine wall;
Placenta increta: in which the placenta penetrates the myometrium (the uterine muscle);
Placenta percreta: the least common type, in which the placenta passes through the uterine wall. It may grow through the uterus and can attach to other organs such as the bladder or the intestines.

The type of placenta accreta can be identified by an obstetrician through the use of diagnostic exams such as ultrasound and MRI.

Common causes

Placenta accreta most commonly results from having had a c-section in the past, which can result in loss of decidua (the mucosal lining of the uterus where the placenta normally implants) in the area of the c-section scar.

Risk factors for placenta accreta include:

Maternal age greater than 35;
Multiple pregnancies;
Uterine myomas (fibroids);
Surgery to remove fibroids;
Prior history of uterine curettage;
Prior history of uterine ablation;
History of pelvic radiotherapy (radiation).

In addition, pregnancies complicated by placenta previa or a history of placenta previa in a prior pregnancy also have an increased risk for developing placenta accreta.

Possible risks

The risks associated with placenta previa depend on when it is diagnosed. The earlier the diagnosis is made, the lower the risk for postpartum hemorrhage and other complications, such as premature birth and the need for an emergency c-section.

Complications of placenta accreta can include infection, problems with coagulation (clotting), rupture of the bladder, and loss of fertility. In addition, placenta accreta that is not diagnosed or managed properly can increase the risk for maternal mortality.

Placenta accreta can also lead to complications for the baby, such as lack of oxygen related to maternal hemorrhage, or complications related to preterm birth.

Treatment options

Treatment for placenta accreta involves a c-section followed by hysterectomy, usually between the 34th and 35th weeks of pregnancy. This is to optimize fetal maturity (development) while minimizing the risk of maternal hemorrhage.

In cases of severe vaginal hemorrhage, the doctor may recommend a blood transfusion.

In some cases, more conservative treatment may be done in order to preserve fertility. This may involve removing the placenta during the c-section but not performing a hysterectomy. These cases require monitoring for bleeding and other complications following the birth.