What is placenta accreta spectrum?

Placenta accreta spectrum, or PAS, affects approximately 1 out of every 533 to 1000 pregnant women in the U.S. – and an estimated 0.05% (up to 7%) of patients with PAS die from the condition.

Dr. Karin Fox, a maternal-fetal medicine specialist in the Division of Maternal-Fetal Medicine at Baylor College of Medicine and the Texas Children’s Pavilion for Women, discusses what causes PAS, who is at risk, and how to look out for symptoms.

Q: What is placenta accreta spectrum?
A: To understand PAS, we must start with a bit about the placenta. It is the organ usually referred to as the “afterbirth” that is unique to pregnancy. It acts as the “life support” for the growing baby by attaching to the lining of the uterus and allowing oxygen and nutrients to pass to the baby.


The placenta accreta spectrum describes a condition in which the placenta not only embeds within the endometrium (or uterine lining) but is attached directly into or deeply through the muscular wall of the uterus. It is named a spectrum, because in some patients, only a small area is involved, in others, it can be extensive. Where the placenta is abnormally attached or invasive, it does not separate normally after delivery. If the placenta shears off, or if some of the uterine wall is removed with the placenta, women may experience heavy bleeding, which can be life-threatening.

Q: Are there any risk factors?
A: The abnormal implantation in PAS occurs most often over a scarred area or endometrial thinning within the uterus that follows uterine surgery. Most often, this follows cesarean delivery, and women with multiple cesarean deliveries have increased risks. Other surgeries that have been associated with PAS include myomectomy (fibroid removal), revision or removal of a uterine septum, endometrial ablation, and radiation of the uterus. In vitro fertilization (IVF), especially with cryopreserved embryos, has also been associated with increased risk.

Q: How is it diagnosed?
A: Most often, PAS is diagnosed with ultrasound, commonly during the second trimester (usually around 18-20 weeks), in which we look at the fetal anatomy and placenta in detail.  Some ultrasound signs may be present as early as the first trimester.  In some cases, MRI may be helpful, but it is not necessarily “better” than ultrasound at detecting PAS. It’s useful, for example, if the placenta cannot be seen fully or seen well on ultrasound.

Studies have shown that in centers that manage PAS regularly and that have a standardized approach to evaluating the placenta, PAS is diagnosed up to 90% of the time prior to delivery. When looking at nationwide data, including smaller clinics and centers, the detection rate prior to delivery drops to about 50%.

We advocate for women to be screened, first based on their clinical history. Women with the risk factors mentioned above benefit from referral to a center with imaging expertise. We also advocate for use of checklists during imaging to ensure that we are looking systematically at the placenta, particularly in patients at risk.

Q: Are there any symptoms or signs?
A: There can be remarkably few symptoms, and the symptoms that women report are often seen in other conditions in pregnancy. Before the invention of ultrasound in the 1960s, there were several small, published case series. The one symptom reported was pain more than expected with normal pregnancy, and occasional bleeding prior to delivery.  Many women experience some pain or discomfort during pregnancy, so this can be a difficult symptom to use in a meaningful way.

Before ultrasound, the most common sign at delivery was abnormal bleeding and shock when the placenta would not separate after birth. The cornerstone of diagnosis is suspecting that a patient is at risk, getting high-quality imaging and planning.

Q: How is it treated?
A: Most women with PAS require delivery by cesarean section, followed immediately by hysterectomy at delivery. Delivery is usually scheduled early, before the onset of labor, to reduce the risk for severe maternal bleeding – usually between 34-36 weeks into pregnancy. About 40% of the patients who have delivered with Baylor and Texas Children’s have required delivery even earlier due to complications such as contractions or bleeding.

In select cases, we can remove the portion of the uterus that is affected and avoid a hysterectomy. The time when we can best determine this is at delivery.

Some patients may opt for true conservative management, where the placenta that is attached is left in place, and the patient is observed over time until the placenta either comes out or gets absorbed by the body. In large studies of this management, up to 58% of women will still require an emergent hysterectomy, and the time to complete resolution can range from within weeks to up to 9 months, and is not without significant, possibly delayed risks.

There is solid evidence that management and delivery in centers with dedicated, multidisciplinary teams and when PAS is detected prior to delivery improves outcomes for women and their babies.

Q: What should you do if you suspect you are at risk?
A: We recommend that patients with risk factors understand their risk and ensure they have a thorough evaluation of the placenta by ultrasound at a center with experience. If you are identified as having PAS prior to delivery, it is important to understand how severe the team anticipates your case may be, and to come in for evaluation for any contractions, bleeding, severe pain, or changes.

If you live far from the hospital, or if your travel time is long, you should consider if you need to move closer to the hospital as delivery nears. Share your questions and concerns with your healthcare team.

Q: Is there anything else you would like to share about this condition?
We may never be able to eliminate all of the clinical factors that increase a patient’s risk for PAS. Some of us will continue to need cesarean deliveries, or will only be able to conceive with IVF, for example. Our primary goal is to understand what causes PAS, research better ways to treat it, educate patients so that they can make the best choices, and advocate for optimal care and support for women.

Dr. Fox is an associate professor of obstetrics and gynecology at Baylor College of Medicine, co-chief of the Maternal-Fetal Surgery Section, and medical director of Maternal Transport at Texas Children’s Hospital. 

Call 832–826–4636 to schedule an appointment with the Maternal-Fetal Medicine team at Baylor and Texas Children’s.

Additional Resources

Learn more about PAS.

See resources at the National Accreta Foundation, the Pan-American Society for PAS, and the International Society for PAS.

-By Nicole Blanton

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