What Is Placenta Accreta Spectrum? Symptoms, Risks and Treatment

There’s no easy way to tell a pregnant woman there’s something wrong with her placenta – the temporary organ that develops to connect the fetus to the uterus.

While rare, a condition called placenta accreta spectrum (PAS) can occur in women with certain risk factors and often requires an early cesarean delivery and hysterectomy. Untreated, the condition can result in hemorrhaging, a leading cause of maternal death worldwide.

“Patients who are facing this diagnosis can be very anxious and overwhelmed,” said Lauren Sayres, MD, assistant professor of OB-GYN-Maternal Fetal Medicine at the University of Colorado Anschutz School of Medicine. It’s why women with PAS receive “whole person care” from a multidisciplinary team at UCHealth University of Colorado Hospital, including specialized surgeons and mental health professionals.

In this Q&A, Sayres shares how placenta accreta spectrum is treated clinically and what her team has learned by tracking cases over the last 15 years.

What is placenta accreta spectrum?

Placenta accreta spectrum is a serious but uncommon condition in pregnancy. PAS involves abnormal invasion of the placenta into the uterine wall as the pregnancy progresses. There are three categories based on severity.

Placenta accreta involves a superficial invasion.
Placenta increta involves a more moderate invasion.
Placenta percreta involves the placenta invading all the way through the uterine wall and potentially into other structures such as the bladder.

PAS is scary, and it’s diagnosed based on ultrasound and MRI. When delivery occurs, it places the patient at high risk of hemorrhage. Patients typically have a hysterectomy after delivering.

What causes placenta accreta spectrum, and what are the risk factors?

PAS is caused by the placenta invading abnormally into the inner uterine wall. The majority of patients who have PAS will have at least one risk factor, such as prior C-section, uterine surgery or a placenta previa (when the placenta develops low in the uterus, partially or completely blocking the cervix). Patients who have multiple gestations, in vitro fertilization (IVF) and multiple pregnancy losses are also at risk. It’s exceedingly rare for a patient to have PAS if they do not have one or more of these risk factors.

How is placenta accreta diagnosed?

The only way to know with 100% certainty is to evaluate the placenta after delivery. But during pregnancy, we have imaging that can help. This includes ultrasound and in certain cases, MRI. Imaging is not 100% accurate – it’s closer to 80%. Many women don't have any signs or symptoms. Vaginal bleeding during pregnancy is the most common symptom.

How is placenta accreta spectrum treated during pregnancy?

Managing placenta accreta is about preparation. As a Placenta Accreta Spectrum Center of Excellence, our team is always prepared to care for patients whether they come in for a scheduled C-section or they come in bleeding and require delivery. Early delivery requires the right surgeons, from the C-section and hysterectomy to managing any bleeding or invasion of the placenta into other parts of the body.

For example, we may need a urologist available if we expect the placenta has invaded the bladder or ureters. We also have specialized anesthesiologists who can help if patients need a transfusion or medications to support blood pressure or control bleeding. And we are always ready to care for the preterm newborn in the neonatal intensive care unit (NICU).

How does placenta accreta spectrum affect babies?

In the PAS cases we’ve tracked over the last 15 years, the average gestational age at delivery has been around 33 to 35 weeks (normal full term is 37 to 42 weeks).

Premature birth is the primary concern for babies, who may need additional support with breathing, feeding or prematurity-related conditions. The severity of these complications depends on the baby's gestational age at birth.

Does placenta accreta always require a hysterectomy?

Typically, yes. There are cases where just a small area of the placenta is involved, and we're able to remove the placenta and use sutures or other measures to control the bleeding. But this is much less common. Most patients will require a hysterectomy.

How does your team support women with PAS?

We anticipate that patients who are facing this diagnosis will need a lot of support. For example, they may need social support if they don’t live locally. They may need help caring for a preterm baby in the NICU, or additional help with a complicated surgical recovery. We involve social workers and case managers. We also have a team in our clinic and in the hospital that attends to patients’ mental health. PAS deliveries are not easy for anyone. We want to be really supportive of the mental health aspects.

Is placenta accreta spectrum cancer?

No, placenta accreta spectrum is not considered cancer as it’s not malignant. It won’t spread through the bloodstream to other parts of the body. But it does act like a cancer where the cells of the placenta are abnormally growing into spaces where they shouldn't be growing. The reason our team includes gynecologic oncologists is because they are expert surgeons. They are able to resect tumors that invade outside of the reproductive organs, as placenta accreta spectrum also can.

Your group has been tracking outcomes data for 15 years. What have you learned?

Our research database includes 300 patients who received care for suspected or confirmed placenta accreta spectrum since 2011. We are tracking risk factors, imaging findings and maternal and neonatal outcomes. Our data show that our rate of diagnosis with ultrasound especially is excellent – though we don’t detect 100% of cases and sometimes we have a suspicion on an ultrasound or MRI that is a false positive.

We have found that patients who experience bleeding or have placenta previa are at the highest risk for unscheduled deliveries.

We've also looked at whether outcomes differ between patients who have scheduled C-sections and those who require unscheduled C-sections, often because of bleeding. About two-thirds of our PAS patients deliver via scheduled C-section.

We've found that even our PAS patients who undergo unscheduled C-sections have had very good maternal and neonatal outcomes. Rates of blood transfusion, ICU admission and maternal or newborn death, as well as length of hospital stay, have been similar between scheduled and unscheduled deliveries. All of these findings suggest that our multidisciplinary placenta accreta spectrum team is working well and is prepared to provide effective care even when patients need an unscheduled delivery.

What do you want patients diagnosed with this condition to understand?

PAS is serious, and it’s manageable. I would encourage anyone diagnosed with PAS to talk to their medical teams anytime they have questions or concerns. Our clinic’s team is always open for referrals.

Key points:

Placenta accreta spectrum (PAS) is a rare but serious pregnancy complication that increases the risk of severe bleeding.

Previous C-sections, uterine surgery and placenta previa are risk factors for PAS.

Ultrasound and sometimes MRI can help identify PAS during pregnancy, allowing specialists to plan delivery.

Treatment often involves a planned cesarean delivery and hysterectomy, with support from a multidisciplinary medical team.

CU Anschutz specialists have tracked 300 patients with suspected or confirmed PAS since 2011, helping inform care for mothers and babies.