Placenta Accreta Spectrum (PAS) – Types, Causes and Treatment

What is Placenta Accreta Spectrum?

Placenta Accreta Spectrum (PAS) refers to a group of obstetric complications involving abnormal attachment of the placenta to the uterine wall. The condition arises when the placenta invades and attaches itself too deeply into the uterine wall, making it difficult to separate during childbirth. PAS is categorized into three main subtypes: placenta accreta, placenta increta, and placenta percreta, each representing different degrees of invasion. Placenta accreta involves an abnormal attachment of the placenta to the uterine wall, placenta increta occurs when the placenta penetrates the uterine wall, and placenta percreta is characterized by the placenta penetrating through the uterine wall and potentially reaching nearby organs.

The prevalence of Placenta Accreta Spectrum has been on the rise, and it poses significant risks during pregnancy and childbirth. Women with previous uterine surgeries, such as cesarean sections, are at a higher risk of developing PAS. The condition can lead to severe bleeding during delivery, requiring advanced medical interventions, such as a hysterectomy. Timely diagnosis through prenatal imaging and careful planning by a multidisciplinary healthcare team are crucial to managing and mitigating the risks associated with PAS.

Types of Placenta Accreta Spectrum

There are three types of placenta accreta spectrum, determined by how deep the placenta has grown:

  1. Placenta accreta – The placenta grows into the lining of the uterus. This is the most common type, occurring in 75 percent of cases.
  2. Placenta increta – The placenta grows into the wall of the uterus.
  3. Placenta percreta – The placenta grows through the wall of the uterus, at times into nearby organs such as the bladder or colon.

This condition can be very serious and may lead to hemorrhaging, organ failure, acute respiratory distress syndrome, and even death. Providers at University of Utah Health are specifically trained to care for patients with placenta accreta.


It is the most common form of placental invasion (~75% of cases). It is thought to occur in approximately 1 in 7000 pregnancies. The incidence is increasing due to the increased practice of cesarean sections. The combination of a previous cesarean section and an anterior placenta previa should raise the possibility of a placenta accreta. This disease has maternal mortality of up to 7% depending on location.


In typical placentation, trophoblast invasion stops at the spongiosus layer of the decidua. There are many theories as to why placenta accreta may occur. One leading theory is that in patients with prior uterine surgeries, the spongiosus layer of the decidualized endometrium may not be present. Therefore, the typical stop signal is absent. Furthermore, cytotrophoblasts must also reach the spiral arterioles before differentiation into placenta tissue may occur. However, uterine scars have a relative lack of vasculature. It is important to note that, although rare, placenta accreta can occur in nulliparous women and women without prior uterine surgery.

Symptoms of Placenta Accreta Spectrum

Placenta accreta spectrum (PAS) is a serious pregnancy complication that may not cause symptoms until delivery. However, there are some signs and symptoms that may indicate the presence of PAS, including:

Abnormal vaginal bleeding: PAS may cause vaginal bleeding during pregnancy, labor, or delivery. The bleeding may be heavy or light, but it is usually painless.

Decreased fetal movement: In some cases, PAS may cause decreased fetal movement. This may be due to reduced blood flow to the fetus.

Uterine tenderness: Women with PAS may experience tenderness or discomfort in the uterus.

Pelvic pain: Women with PAS may experience pelvic pain or discomfort.

Anemia: Heavy bleeding from PAS can cause anemia (a deficiency of red blood cells).

Abnormal fetal position: PAS may cause the baby to be in a breech (bottom-first) or transverse (sideways) position.

Preterm labor: PAS may cause preterm labor (labor that occurs before 37 weeks of pregnancy).

It is important to note that not all women with PAS will experience symptoms, and some symptoms may be due to other conditions. Pregnant women who are at increased risk for PAS should be closely monitored throughout pregnancy and delivery to ensure early detection and management of any complications.

Causes of Placenta Accreta Spectrum

Placenta Accreta Spectrum (PAS) is primarily associated with factors that affect the normal implantation of the placenta into the uterine wall. Several risk factors increase the likelihood of developing PAS:

  1. Previous Uterine Surgeries: Women with a history of uterine surgeries, particularly multiple cesarean sections, are at an elevated risk of PAS. The scar tissue left by these surgeries can disrupt the normal implantation of the placenta.
  2. Advanced Maternal Age: Older maternal age is considered a risk factor for PAS. As women age, the integrity of the uterine wall may be compromised, increasing the chances of abnormal placental attachment.
  3. Uterine Abnormalities: Conditions such as uterine anomalies or a malformed uterus can create an environment conducive to abnormal placental attachment.
  4. Placenta Previa: Women with placenta previa, a condition where the placenta partially or completely covers the cervix, have an increased risk of developing PAS.
  5. Inflammation and Scarring: Inflammation or scarring within the uterine wall, often due to conditions like endometritis, can disrupt the normal implantation process, leading to PAS.
  6. Multiparity: Women who have had multiple pregnancies may be at a higher risk of developing PAS, possibly due to repeated stretching and thinning of the uterine wall.
  7. Assisted Reproductive Technologies: Women who have undergone fertility treatments, such as in vitro fertilization (IVF), may be at a slightly higher risk of PAS.
  8. Maternal Trauma: Trauma or injury to the uterus, whether from accidents or medical procedures, can increase the risk of abnormal placental attachment.

It’s important to note that the exact cause of PAS is not always clear, and often a combination of these risk factors may contribute to the development of the condition. Early detection through prenatal screening and close monitoring during pregnancy are crucial for managing and addressing potential complications associated with Placenta Accreta Spectrum.


Placenta accreta is considered a high-risk complication of pregnancy and can cause the following:

  • Excessive bleeding before, during, or after delivery that may require a blood transfusion and a stay in the intensive care unit
  • Preterm delivery
  • A prolonged hospital stay, possibly before delivery
  • Hysterectomy (surgical removal of the uterus) which prevents future childbearing
  • Surgical injury to organs including the intestines, bladder and ureter

Depending on their gestational age at the time of delivery, your baby may also need to stay in our neonatal intensive care nursery (ICN).

Risk factors of Placenta Accreta Spectrum

The estimated incidence (how often it happens) of Placenta Accreta Spectrum (PAS) pregnancies has quadrupled since the 1980s, increasing from 1 in 1250 births to 1 in 272 births. As the overall cesarean delivery rate in the United States has continued to rise, the rates of PAS have risen in parallel. Certain women are at higher risk for PAS:

  • Women who have had previous cesarean birth
  • Women with previous uterine surgery (example: myomectomy, dilation & curettage)
  • Women over the age of 35 years
  • Women who have had multiple previous pregnancies
  • The placenta position/location in the uterus – risk increases if your placenta covers your cervix (placenta previa) or sits on the lower portion of your uterus

Diagnosis and tests

Diagnosing Placenta Accreta Spectrum (PAS) involves a combination of clinical evaluation and imaging studies. The following methods are commonly employed by healthcare professionals to diagnose PAS:

Ultrasound Imaging

  • Transabdominal Ultrasound: This is a standard ultrasound procedure that involves placing a transducer on the abdomen to visualize the uterus and placenta. However, accurate diagnosis can sometimes be challenging due to the limitations of transabdominal imaging.
  • Transvaginal Ultrasound: This method involves placing a specialized ultrasound probe into the vagina for a more detailed and close-up view of the uterine wall and placenta. Transvaginal ultrasound is often more accurate in diagnosing PAS, especially in early stages of pregnancy.

Color Doppler Ultrasound

This specialized ultrasound technique assesses blood flow within the placenta and surrounding tissues. Abnormal blood flow patterns can be indicative of placental abnormalities, including PAS.

Magnetic Resonance Imaging (MRI)

MRI provides detailed images of the structures within the pelvis and can help in identifying the extent of placental invasion. It is often used when ultrasound results are inconclusive or when a more comprehensive evaluation is needed.

Prenatal Screening

Routine prenatal screenings, including a thorough review of the patient’s medical history and risk factors, are essential in identifying individuals at a higher risk for PAS. Women with a history of uterine surgeries or other risk factors may be monitored more closely.

Invasive Procedures

In certain cases, especially when there is a high suspicion of PAS, healthcare providers may opt for more invasive procedures, such as a diagnostic hysteroscopy or a saline-infusion sonogram. These procedures can provide a direct view of the uterine cavity and aid in confirming the diagnosis.

Early and accurate diagnosis of PAS is crucial for proper management and planning of the delivery. A multidisciplinary approach involving obstetricians, radiologists, and other specialists is often necessary to ensure the best possible outcome for both the mother and the baby. Regular prenatal care, especially in high-risk pregnancies, plays a key role in the timely detection and management of Placenta Accreta Spectrum.

How to treat placenta accreta spectrum?

The treatment of Placenta Accreta Spectrum (PAS) often involves a multidisciplinary approach and careful planning to minimize the risks associated with the condition. The specific treatment plan may vary depending on the severity of the placental attachment and the overall health of the mother and the baby. Here are common approaches to managing PAS:

Scheduled Cesarean Section

In many cases of PAS, a planned cesarean section is recommended to minimize the risk of uncontrolled bleeding during childbirth. The timing of the cesarean section is usually determined based on the gestational age of the fetus and the extent of placental invasion.


A hysterectomy, or the surgical removal of the uterus, is often considered a definitive treatment for severe cases of PAS. This procedure may be necessary to control life-threatening bleeding and is more likely in cases of placenta percreta, where the placenta penetrates through the uterine wall.

Uterine Artery Embolization

In some cases, uterine artery embolization may be performed to reduce blood flow to the uterus, helping to control bleeding. This procedure involves injecting material into the blood vessels supplying the uterus to block or reduce blood flow.

Selective Uterine Preservation

In situations where fertility preservation is a concern, efforts may be made to preserve a portion of the uterus while removing the affected area. This approach is generally considered in cases where the placental invasion is limited, and the woman desires future pregnancies.

Intraoperative Blood Conservation

Given the risk of significant blood loss during surgery for PAS, strategies to conserve blood, such as preoperative blood donation, cell salvage techniques, and careful monitoring, may be employed.

Neonatal Considerations

The neonatal care team may be involved to ensure the well-being of the baby, especially in cases where preterm delivery is necessary. Neonatal intensive care may be required for babies born prematurely.

It’s important to note that the choice of treatment depends on the individual case, and decisions are often made collaboratively by a team of healthcare professionals, including obstetricians, maternal-fetal medicine specialists, radiologists, and anesthesiologists.

Prevention of Placenta Accreta Spectrum

Preventing Placenta Accreta Spectrum (PAS) involves minimizing risk factors and addressing potential issues early in pregnancy. While not all cases can be prevented, certain measures can help reduce the likelihood of developing PAS. Here are some simple points for prevention:

  • Limit Cesarean Sections: When possible, aim to limit the number of cesarean sections. Discuss delivery options with your healthcare provider and explore the possibility of vaginal birth after cesarean (VBAC) if appropriate.
  • Optimize Reproductive Health: Maintain good reproductive health by managing and treating conditions such as uterine infections promptly. Seek early medical attention for any gynecological issues.
  • Healthy Pregnancy Planning: Plan pregnancies thoughtfully, allowing adequate time between pregnancies. This can help reduce the strain on the uterus and decrease the risk of PAS.
  • Regular Prenatal Care: Attend regular prenatal check-ups to monitor the progress of your pregnancy. Early detection through ultrasound and other screening methods can help identify potential issues.
  • Discuss Previous Surgeries: Inform your healthcare provider about any previous uterine surgeries, including cesarean sections. This information is crucial for assessing your risk and planning appropriate care.
  • Manage Risk Factors: If you have risk factors for PAS, such as advanced maternal age or a history of placenta previa, work closely with your healthcare team to manage these factors and monitor your pregnancy more closely.
  • Healthy Lifestyle: Adopt a healthy lifestyle with a balanced diet, regular exercise, and adequate rest. This can contribute to overall reproductive health.
  • Seek Expert Care: If you have concerns about your pregnancy or reproductive health, consult with specialists such as maternal-fetal medicine experts or obstetricians with experience in high-risk pregnancies.
  • Educate Yourself: Stay informed about PAS and its risk factors. Understanding the condition can empower you to make informed decisions and collaborate with your healthcare team.
  • Fertility Counseling: If you have undergone fertility treatments or assisted reproductive technologies, consider seeking fertility counseling to understand potential risks and make informed decisions about family planning.

It’s essential to recognize that while these measures can contribute to reducing the risk of PAS, some factors may be beyond control. Therefore, early and regular prenatal care, along with open communication with healthcare providers, remains crucial for the best possible pregnancy outcomes.

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