Introduction

Placenta accreta is the abnormal growth of all or part of the placenta into the uterine wall called myometrium. This condition occurs during pregnancy and can be life-threatening because the placenta, which provides nutrients and oxygen for the baby in the womb (uterus), attaches too deeply to the uterine wall. Placenta accreta is known to be among the causes of maternal death and other associated diseases in women. It could also result in severe bleeding that would require frequent blood transfusions.¹

There are different forms of placenta accreta (placenta invasion) and they are grouped based on their severity:

• Placenta accreta: This is the mildest and most common form, with an occurrence rate of about 75%. In placenta accreta, the placenta does not invade the uterine muscle but remains attached to it.
• Placenta increta: This is the second form, occurring in approximately 25% of cases. In placenta increta, the placenta attaches itself to the uterus and partially invades the muscles of the uterine wall.
• Placenta percreta: This is the most complicated form of placenta invasion. The placenta in this case penetrates through the uterine muscles and may extend into the outermost layer of the uterus (uterine serosa). Placenta percreta has the least number of occurrences with 5% cases.

Importance of early diagnosis and treatment

Early diagnosis of placenta accreta is important for improving outcomes for both mother and child. Key benefits of early diagnosis include:^2,3,4

Better counselling and treatment options

• Early detection through diagnosis, even in the first trimester, allows for an in-depth discussion of potential risks, complications, and available treatments with the patient.
• The patient may be given a chance to decide if they would want to end the pregnancy if it is discovered early, especially if there would be many complications associated with it.

Decreased chronic illness and death among mothers

• Placenta accreta has a maternal death incidence of about 6% and is a major cause of 33% to 50% of emergency peripartum hysterectomies, a process where a part or all of the uterus is removed during or within 24 hours of delivery.
• Life threatening haemorrhage can be avoided with early identification, which also lessens the need for multiple blood transfusions.

Improved planning among multidisciplinary professionals

• Timely diagnosis gives time to an experienced multidisciplinary team comprising obstetricians, anesthesiologists, interventional radiologists, neonatologists, and blood bank specialists to prepare a comprehensive care plan that would benefit the patient. 
• Involving these teams of professionals in the early diagnosis will help them organise better delivery plans and prepare for potential complications that may arise during or after delivery. 

Management strategies

• In cases without significant bleeding, conservative therapy, such as leaving the placenta in situ, may be considered to preserve future fertility.
• Early diagnosis enables close monitoring and follow-up.

Risk factors to placenta accreta 

Previous caesarean delivery 

A history of caesarean delivery increases the risk of placenta accreta. Studies show that the risk rises from 0.3% in women with one caesarean section to 0.69% in those with five or more caesarean deliveries.^1,5 

Placenta previa 

Placenta previa, a condition where the placenta partially or completely covers the cervix, is another significant risk factor. The risk of placenta accreta is approximately 3% in women with placenta previa alone. This risk increases substantially if the woman has had both placenta previa and multiple previous caesarean deliveries.^1,6 

Smoking during pregnancy 

Smoking while pregnant is also linked to an elevated risk of placenta accreta.⁵

Uterine Anomalies

Structural abnormalities in the uterus may also increase the likelihood of placenta accreta.⁵

Maternal Age

Advanced maternal age is one of the numerous risks of placenta accreta.⁷ 

Diagnosis of placenta accreta

Placenta accreta is mostly diagnosed during pregnancy using ultrasound or MRI, although detection before delivery is not always ideal. Key diagnostic methods include:^1,6

Ultrasound 

The ultrasound (standard transabdominal ultrasonography) is the primary and most reliable tool in the early detection of placenta accreta. While ultrasound can sometimes enable healthcare professionals to identify features of placenta accreta in the first trimester, most cases are detected in the second and third trimesters. The most significant association of ultrasonographic detection of placenta accreta is the placenta previa which occurs in more than 80% of cases. Other findings that increase the chances of placenta accreta shown in the ultrasound tool include:

• Irregular vascular spaces that give a Swiss-cheese appearance (placental lacunae)
• Decreased retroplacental myometrial thickness (<1 mm)
• Abnormalities of the uterine serosa-bladder interface
• Placenta extension into the myometrium, serosa, or bladder

Magnetic Resonance Imaging (MRI)

MRIs are used mostly when the findings of ultrasound are not clear enough. It is also used when it is suspected that there is penetration or invasion of the parametrium or any surrounding organ. Findings in MRI that suggest the presence of placenta accreta include:

• The presence of black intraplacental bands on T2 weighted images
• Abnormal uterine bulging
• Heterogeneity (consisting of different elements) of signal intensity within the placenta's body

Management and treatment options available

Early diagnosis 

Timely diagnosis helps in the appropriate management of placenta accreta, allowing healthcare professionals to develop the best delivery options that would be best for the patient. This also helps to reduce bleeding and other potential complications.⁶

Caesarean hysterectomy

Studies show that this is the most effective treatment for placenta accreta. It involves performing a caesarean section to deliver the baby, followed by surgical removal of the uterus with the placenta left intact to prevent life-threatening bleeding.^6,8 

Conservative Management

This management option is considered by mothers who may want to get pregnant in the future and as such close monitoring is required. In this management plan, both the uterus and placenta are left in situ, allowing the placenta to be reabsorbed over time. The major challenge with this treatment option is that there is a high risk of infection.⁶ 

Other treatment options

• The use of medications such as methotrexate can help break down placental tissue. It can be used in some placenta accreta cases, although its effectiveness is unclear.
• Surgical removal of the placental can be employed as well, along with a portion of the uterine wall. This procedure is possible only in situations where there is limited placenta invasion. However, there is a high risk of bleeding in patients.⁶  

FAQs

What are the symptoms of placenta accreta during pregnancy? 

Placenta accreta does not show any form of symptoms but it may present bleeding during the third trimester. 

How common are placenta accretas? 

Currently, the occurrence rate of placenta accreta is recorded to be 1 in 533 pregnancies.

Does placenta accreta affect pregnancy? 

Yes, to a large extent, placenta accreta may affect pregnancy by increasing the chances of birthing a preterm baby, severe bleeding during delivery and fertility complications.

Summary 

Due to the serious complications associated with placenta accreta, including increased maternal death, and other complications linked to placenta accreta, it is important that patients with risk factors such as placenta previa and prior caesarean delivery get early screening with ultrasound to promote effective diagnosis and management. Early diagnosis of placenta accreta, even in the first trimester, promotes improved patient counselling, reduced maternal morbidity and mortality, better collaborative planning, and consideration of treatment options.