What Is Placenta Accreta?

Placenta accreta—also known as placenta accreta spectrum and formerly known as morbidly adherent placenta—is a pregnancy complication where the placenta becomes firmly embedded within the uterine wall. This becomes especially problematic when the placenta does not detach spontaneously after delivery and instead must be removed from the uterus surgically—a procedure that can cause potentially life-threatening bleeding.

Doctor listening to belly of pregnant person

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Types of Placenta Accreta

There are three types—also referred to as "grades"—of the placenta accreta spectrum, categorized based on how deeply the placenta is attached to the uterus:

  • Placenta accreta (Grade I): The placenta is firmly attached to the uterine wall of the uterus. This is the most common and least serious of the three types.
  • Placenta increta (Grade II): The placenta is more deeply embedded in the uterine wall and is attached to the muscle of the uterus.
  • Placenta percreta (Grade III): The placenta grows through the uterine wall, potentially impacting other organs like the bladder or intestines. It's the most severe type of the condition.

Signs and Symptoms of Placenta Accreta

Part of what makes placenta accreta so difficult to manage is that, in most cases, there are no signs or symptoms of the condition. There are two exceptions to this:

  • Placenta previa: This is when the placenta covers all or part of the opening of the pregnant person's cervix, and it frequently develops alongside placenta accreta. Placenta previa often causes vaginal bleeding, so if a pregnant person is experiencing unexplained vaginal bleeding, it could be a sign of placenta previa and potentially placenta accreta.
  • Placenta percreta: This is the most severe of the three grades of placenta accreta when the placenta penetrates and eventually grows through the uterine wall. If this happens, it can cause bladder or pelvic pain for the pregnant person and occasional blood in the urine.

Causes and Risk Factors

While there is not, at this point, a single established cause of placenta accreta, those in the medical profession have identified several risk factors. As rates of placenta accreta have increased steadily since the 1970s, researchers have tracked the conditions that appear to correlate with these higher rates and identified the following risk factors:

  • Previous cesarean section: The risk of placenta accreta spectrum increases with the number of prior cesarean (C-section) deliveries a person has had. Specifically, one study found that the rate of placenta accreta spectrum increased from 0.3% in people with one previous cesarean delivery to 6.74% for people with five or more C-section deliveries.
  • Abnormal position of the placenta in the uterus: Including placenta previa
  • Being over 35 years of age
  • Previous uterine surgery: Including fibroid removal or treatment of uterine scar tissue
  • Pregnancy via in-vitro fertilization

Diagnosis

Like many other conditions, earlier diagnosis of placenta accreta can result in better outcomes for both the pregnant person and the fetus. In most cases, placenta accreta is diagnosed via an ultrasound.

In other cases, placenta accreta is not visible on an ultrasound, and magnetic resonance imaging (MRI) may be used instead.

When Is Placenta Accreta Typically Diagnosed?

While some features of placenta accreta may be visible using ultrasonography in the first trimester, most diagnoses are made in the second and third trimesters.

If a person is at high risk for the condition, their healthcare team should not only continuously monitor their pregnancy but also make sure that some type of imaging is done.

Potential Complications

Placenta accreta has the potential to result in several complications and/or risks for both the pregnant person and the fetus—some of which can be fatal. Possible complications for the fetus can include:

  • Premature birth: Typically between 34 and 37 weeks of gestation (or three to six weeks early), depending on the severity of the condition
  • Admission to a newborn intensive care unit: Although their overall prognosis is good
  • Unstable condition in utero: While the accreta itself is not directly harmful to the fetus, it can cause heavy bleeding in the pregnant person, making both parties unstable.

Potential risks and complications for the pregnant individual can include:

  • Hemorrhaging: Severe bleeding may occur if the pregnant person also has placenta previa and/or following attempts to remove the placenta embedded within the uterus. In some cases, the patient may require a blood transfusion, and without careful treatment by experienced healthcare professionals, the bleeding may end up being life-threatening.
  • Required C-section: Typically, when placenta accreta is diagnosed before labor begins, the medical team may recommend a C-section—a procedure that comes with its own set of risks and one that the pregnant person may not have chosen under normal delivery circumstances.
  • Hysterectomy: Sometimes, in situations where it's clear that it's impossible to safely detach the placenta from the uterus, the uterus must be surgically removed to stop blood loss.
  • Infertility: If a hysterectomy is required, it will limit a person's future reproductive options, including becoming pregnant and giving birth. However, in some cases, surgeons are able to leave the person's ovaries intact to allow different fertility options or premature menopause.
  • Pelvic organ damage: In severe cases of placenta accreta, the placenta grows through the walls of the uterus and can harm nearby organs—including the bladder, intestines, kidneys, and liver—during pregnancy as well as labor and childbirth.

Treatment

Although early diagnosis allows the pregnant person and their medical team to prepare for what could be a complicated labor and delivery, currently, there are no options to treat the condition in utero. In that case, the patient will be closely monitored throughout their pregnancy.

Sometimes, a person's healthcare provider will recommend that they schedule a C-section a few weeks ahead of their due date in order to decrease the risk of bleeding from contractions or labor.

When the time for delivery arrives, the pregnant person's medical team will assess their situation—including how difficult it would be to remove the placenta—and then determine the safest option. In some cases, that's a hysterectomy, because removing the uterus and the placenta together, while they're still attached, can reduce the risk of hemorrhaging. In others, though, it's possible to surgically remove the placenta without having to remove the uterus along with it.

A Word From Verywell

If you receive a diagnosis of placenta accreta, know that your medical team will set up a plan that is best for you and your baby.

With an ever-expanding set of tools and technologies, medical professionals have never been better equipped to safely deliver your baby.

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Article Sources
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  2. Cleveland Clinic. Placenta accreta. Updated April 18, 2018.

  3. Brigham and Women's Hospital. Placenta accreta.

  4. American College of Obstetricians and Gynecologists. Placenta accreta spectrum. Updated 2021.