What Is Placenta Percreta?

Overview

Placenta percreta occurs during pregnancy and is the most severe subtype of the placenta accreta spectrum (PAS), the abnormal attachment of the placenta to the wall of the uterus.¹ The placenta is an organ that forms in the uterus during pregnancy, responsible for providing oxygen and nutrients to a developing baby. Typically in pregnancy, the placenta will detach itself from the uterine wall after your baby is born. However, in this condition, the placenta does not separate easily after delivery. 

Although rare, placenta percreta can be life-threatening, involving serious complications for pregnancy and maternal well-being. PAS is associated with a maternal morbidity of 24-67% and mortality of 7%.² It often occurs without symptoms and cannot be prevented. The incidence of this placenta percreta has increased over the years, therefore understanding this condition is important. 

This article will detail the causes, symptoms and diagnosis of placenta percreta. Read on to find out what this condition can mean for you and your baby, prognosis and the treatment options available to you. 

What is placenta percreta?

Placenta percreta is the most severe type of placenta accreta and is considered a high-risk pregnancy complication. When diagnosed with this condition during pregnancy, an early caesarean section (C-section) may be required alongside a hysterectomy (removal of the uterus). 

PAS can be categorized into three types based on placental invasion of the uterus and their severity:

• Placenta accreta –this is the most common and mildest type. The placenta attaches to the wall of the uterus, but it does not pass through the uterine wall or impact the myometrium (uterine muscles)
• Placenta increta –the placenta is embedded in the wall of the uterus where it firmly attaches itself to the myometrium. It still does not pass through the uterine wall. 17% of cases of PAS are placenta increta³
• Placenta percreta –the placenta passes through the uterine wall, growing on your uterus and impacting other organs, such as the intestines or bladder. It is the most severe type and accounts for around 5% of cases³

Causes of placenta percreta

The exact cause of placenta percreta is unknown and it cannot be prevented. However, it is associated with some clinical situations, which are known to increase the likelihood of developing the condition. 

Common risk factors

A common risk factor for developing placenta percreta includes those who have uterine scarring or damage as a result of previous uterine surgeries and placenta previa. 

Multiple C-section deliveries

Those who have had multiple C-sections have a higher risk of developing placenta percreta.⁴ This is because scarring of the uterus that results from C-sections may interfere with the normal implantation of the placenta, thus increasing the risk of abnormal placenta attachment. The incidence of developing this condition increases with the number of previous C-sections, from 0.3% with 1 previous C-section delivery to 6.7% in those with 6 previous C-section deliveries.⁵

Previous surgeries on their uterus 

Similarly to C-sections, prior surgeries on the uterus can cause uterine scarring, increasing the risk of developing placenta percreta. Uterine surgeries can include myomectomy (removal of uterine fibroids), curettage (removal of tissue from the uterus), and operative hysteroscopic procedures.⁴

Placenta previa 

Placenta previa is a condition where the placenta partially or completely blocks the cervix and occurs in an estimated 0.3 to 2% of pregnancies.⁶ The implantation of a zygote (fertilised egg) requires an oxygen and collagen-rich environment, which prior uterine scars provide.

This allows for the adherence to the uterine scar, blocking of the cervix and invasion of myometrium by the placenta.⁶ Those with placenta previa and a history of multiple C-section deliveries have a greater risk of placenta percreta.⁵ A study showed that the risk increases from 11% after 1 C-section delivery to 60% after 3 or more deliveries.⁵

Other risk factors

Other risk factors known to contribute to developing placenta percreta include⁴

• Pregnancies via IVF
• A placenta in an abnormal location in their uterus 
• Advanced maternal age
• Postpartum endometritis
• Asherman’s syndrome, characterised by a damaged uterine lining 

Symptoms of placenta percreta 

Placenta percreta mostly occurs without symptoms, especially in the early stages of pregnancy, meaning it can often go unnoticed until scans take place. However, as the condition progresses, some have noted dull and continuous lower abdominal or pelvic pain during the third trimester (weeks 28-40 of pregnancy), alongside frequent urination and blood in the urine.³ 

Diagnosis and tests

Placenta percreta is sometimes discovered at the time of delivery, accompanied by severe blood loss. It is noted to be the leading cause of postpartum haemorrhage and an indication for a hysterectomy. Several antenatal diagnosis methods can be performed by your clinician.

Ultrasounds 

Transabdominal and transvaginal ultrasounds are the primary tools used to identify features of placenta percreta during routine appointments. In the first trimester, results may show a low-lying uterine sac with a thin myometrium below 1 mm.

The second and third trimesters may show an irregular border between the bladder and myometrium, bulging of the placenta into surrounding organs of the uterus causing a mass-like lesion to protrude out of the uterine wall and the presence of several lacunar spaces (irregular vascular spaces) in the placental implantation area.^3,7 

Magnetic resonance imaging (MRI) 

MRIs are used in conjunction with ultrasounds as they better predict placental tissue invasion into nearby pelvic tissues and the bladder. They are often used to differentiate between the three subtypes of placenta accreta.⁷

Colour doppler imaging 

This method can assess the presence of a turbulent blood flow into placental lacunar spaces, thinning of the myometrium and the intervention of placental tissue into the bladder wall.⁷ 

Cystoscopy 

A cystoscopy is used in assessing the severity of placenta accreta especially when placentation is over a previous uterine scar in proximity to the bladder wall, and the presence of bulging of the bladder.⁸

Importance of early diagnosis

Early detection of placenta percreta is vital in decreasing blood loss at delivery and postpartum complications. Early diagnosis allows for proactive planning of your pregnancy and delivery with your clinician to combat risks associated with the condition. Having the correct people involved can help in planning the following:

• Postpartum haemorrhage
• Premature birth 
• Close monitoring of the growth of the baby 
• Surgical intervention, including surgical planning and preparation
• Monitoring of maternal health with regular ultrasounds to monitor the condition

The outlook of placenta percreta is generally good when a diagnosis is made early on in pregnancy. 

Placenta percreta treatment and management

Treatment options for placenta percreta can vary and often involve a multidisciplinary approach to mitigate risks and optimise maternal and neonatal outcomes.^4,9

If diagnosed before delivery, you will be closely monitored for the rest of your pregnancy. This involves: 

• Delivery planning with your obstetrician and gynaecologist. Risks and potential complications are usually discussed with the possibility of needing a blood transfusion before or after delivery and being admitted to an intensive care unit (ICU) due to severe bleeding
• C-section delivery will be scheduled between 34-37 weeks of pregnancy to minimise the risk of severe blood loss from contractions and going into labour
• Due to potential haemorrhage, it may be important to optimise pre-delivery haemoglobin levels and correct iron deficiency anaemia
• Being hospitalised or put on bed rest to prevent premature delivery from vaginal bleeding during the third trimester

Surgery for placenta percreta

In severe cases, surgical intervention may be the only option to remove the placenta and control bleeding. Surgical options include a caesarean hysterectomy or removal of the placenta whilst preserving the uterus.

Caesarean hysterectomy 

This is a non-conservative approach as the uterus is removed at the same time as delivery. Removal of the uterus with the placenta attached minimises the risk of haemorrhaging. With a hysterectomy, you can no longer become pregnant. It is typically the last resort and common in those who do not wish to conceive in the future, therefore it is important to discuss childbearing options with your clinician.⁴

Removal of the placenta whilst preserving the uterus 

This conservative option may be favourable to those with less extensive placental invasion who wish to preserve their fertility. However, it is associated with increased morbidity, infection, haemorrhage and requirement for emergency hysterectomy.² Although, studies show potential in reducing the complications associated with hysterectomy, such as injury to nearby pelvic organs and massive obstetric haemorrhage.⁴ 

What are the complications of placenta percreta?

Placenta percreta is considered a high-risk pregnancy with several complications for both mother and baby.¹

Maternal complications

• Severe bleeding before, during, or after childbirth that may require a blood transfusion
• Requirement of a C-section and other procedures to remove the placenta to avoid losing too much blood
• Lactation failure due to loss of hormones in the blood as a result of blood loss. This includes prolactin which is a protein responsible for lactation
• The requirement of a hysterectomy which may be the only solution in the removal of the placenta

Complications for the baby

• Scheduled birth 3-6 weeks early depending on the severity of placenta percreta and whether placenta previa is diagnosed
• Premature birth due to heavy bleeding. This means there is an increased risk of the baby being admitted to ICU with respiratory troubles and problems gaining weight

Summary

Placenta percreta is the most severe subtype of placenta accreta, characterised by the abnormal attachment and invasion of the placenta to the uterine wall that does not separate after delivery. Common risk factors include previous uterine surgeries such as multiple C-sections, placenta previa, pregnancy via IVF, and advanced maternal age. 

Placenta percreta usually develops without symptoms but can be detected during routine scans to avoid complications at the time of delivery, including haemorrhage and hysterectomy. 

Treatment options involve close monitoring for the duration of pregnancy with careful delivery planning, and surgical intervention such as caesarean hysterectomy or removal of the placenta whilst preserving the uterus. Early diagnosis is crucial in ensuring the best outcomes and reducing the risks of placenta percreta in a pre-planned manner.