What Is Placenta Accreta?

Pregnancy is a beautiful phase of life, but it does come with some complications. Placenta accreta spectrum (PAS) or abnormal invasion of placenta (AIP)  is one of the complications that can happen during pregnancy. This condition refers to the abnormal growth of the placenta in the uterus’ muscular wall. Placenta accreta spectrum disorders can be classified by their degree of invasion in the uterus’ muscular wall, ranging from risks posed as mild to serious towards the patients and their babies.¹ 

Placenta accreta, placenta increta or placenta percreta all come under PAS.

Placenta

The placenta is a temporary organ formed in a pregnant woman's uterus during the first three months of pregnancy. It weighs around 500 grams. It is around 2.5 cm thick and 22 cm in diameter. It helps in transporting oxygen and nutrients to the foetus during the pregnancy. In the early weeks of pregnancy, there is an increase in food intake and stored energy. In the advanced weeks of pregnancy, it prepares for foetal growth. The placental membrane helps in the exchange of the following things between the mother and the foetus.²,³

• Gases
• Electrolytes
• Foetal waste
• Maternal antibodies
• Hormones
• Water
• Amino acids
• Glucose
• Vitamins
• Free fatty acids

Types of placenta accreta

Placenta accreta disorders are on the rise nowadays, especially with caesarean section deliveries.⁴,⁵

• Placenta accreta: This accounts for around 75% of the cases. Placental villi, which consists of three layers with different types of cells and these are in contact with the mother’s blood, attaching to less than 50% of the myometrium, the muscular wall of the uterus.
• Placenta increta: It accounts for around 18% of the cases. It happens when more than 50% of the myometrium is invaded.
• Placenta percreta: It accounts for around 7% of the cases. In this, the placenta attaches to the serosa (a single outer cell layer of tissue made of epithelial cells that envelop the uterus)⁶ and nearby organs.

Sometimes, invasion happens beyond the uterus. Different health conditions can be associated with the placenta and its position during pregnancy and after childbirth. 

• Low-lying placenta: If the placenta stays low and near the cervix, it may block the baby's way out of the womb. The placenta is around 2 cm away from the cervix. 
• Placenta previa:  When the placenta completely covers the cervix, it is termed placenta previa. It affects around every 1 in 200 births. 
• Retained placenta: After childbirth, the placenta is usually expelled from the body. But, in some cases, the placenta is not expelled, which might cause heavy bleeding and some complications.
• Placental abruption: In this, the placenta comes away from the uterus wall. It can cause pain and bleeding from the vagina. It increases the chances of premature birth, stillbirth or growth issues.⁵

Risk factors for placenta accreta

Placenta accreta is associated with the following risk factors.⁴,⁵

• Surgery of the endometrium
• Caesarean surgery
• Hysteroscopy (procedure to check inside the uterus)
• Endometrial ablation
• Curettage
• Placenta praevia with a history of c-section
• In vitro fertilisation
• Multiparity
• High maternal age
• Myomectomy (procedure of removing uterine fibroids but preventing infertility)
• Smoking
• Hypertension

Signs and symptoms

Signs and symptoms of placenta accreta spectrum are not so profound. Vaginal bleeding in the third trimester can be a sign of complication. Diagnostic tests can help to rule out the condition.

Diagnosis

If the patient comes under the risk category or if they are experiencing pain and bleeding, healthcare providers will perform some diagnostic procedures to rule out this condition:⁴^,7

• Ultrasound: Ultrasound is a radiological procedure that uses sound waves to produce images of the body. It can help visualise placenta praevia and invasion of the placenta into the serosa or bladder and any other abnormalities. Around 50% of cases are diagnosed antenatally in the UK. This can provide an opportunity to plan the management of this condition.
• Colour Doppler: It is a diagnostic procedure where sound waves are converted to colourful images of the body. The colours can indicate the speed and direction of blood flow. It can help reveal lacuna (irregular fluid-filled appearance within the placenta often seen as a moth-like appearance) where the placenta’s tissue has grown deeply in the uterus's muscular wall and caused a strong blood flow in the placenta.⁸
• Magnetic resonance imaging (MRI): It is a diagnostic procedure that uses magnetic fields and radio waves to create images of the body. MRI has 84% specificity and 94.4% sensitivity in diagnosing placenta accreta. It can provide more detailed information about the extent of invasion in posterior placenta cases or invasion beyond uterine serosa.

Management and treatment

If placenta accreta is diagnosed, healthcare providers must make a management and treatment plan. Chances of preterm birth are higher in such cases. If this condition is diagnosed antenatally, it becomes easier to manage than postnatally. To minimise risk and ensure maturity of the foetus, it is recommended to perform a c-section between 34-35 weeks of pregnancy. Management of the condition depends on the patient's condition, severity and extent of invasion, and availability of specialised centres nearby. In case of bleeding, arrangements should be made to have ample blood supply for transfusion purposes. The patient’s haemoglobin level should be optimised before engaging in the delivery process.⁴,⁷

• Caesarean section: Depending on the condition of the patient, a caesarean delivery is planned around 34-35 weeks of pregnancy. It would be better to have the delivery in a hospital with perinatologists, pelvic surgeons, general surgeons, neonatologists and urologists available for emergencies. The uterine incision should avoid the placenta. 
• Hysterectomy: Hysterectomy refers to a surgical procedure where the uterus is removed. It can be a total, subtotal or radical hysterectomy.  Total hysterectomy is mostly performed where the cervix and womb are completely removed. In a subtotal hysterectomy, the main body of the womb is removed with the cervix still intact. In radical hysterectomy, the womb and surrounding tissues are removed. Peripartum hysterectomy refers to a hysterectomy performed during or shortly after childbirth. This procedure carries the risk of damage to nearby organs such as ureters and bladder. It can result in loss of fertility and chances of vaginal prolapse.
• Retention of the placenta: An incision is made at the upper margin of the placenta, and the foetus is delivered. No attempt should be made to remove the placenta physically or by giving oxytocin. This procedure minimises intra-operative bleeding, but it can cause secondary haemorrhage. It can take up to 20 weeks for the placental tissue to be absorbed by necrosis. There mayt be chances of an emergency peripartum hysterectomy. Antibiotics are administered to avoid infection.
• Triple p procedure: It is a surgical procedure done to avoid the complications of peripartum hysterectomy. It has three steps - perioperative placental localisation, pelvic revascularisation and placental non-separation and myometrium excision. In simple words, it means trying not to separate the placenta from the underlying myometrium by removing as much placental tissue as possible. It might minimise the risk of bleeding and infection.⁹

Complications

The Placenta accreta spectrum can lead to postpartum haemorrhage. Blood transfusions are required in the majority of the cases. Patients need to be carefully monitored in the intensive care unit (ICU) to keep an eye out for any complications. Sometimes, surgical procedures can damage nearby organs and tissues. In some cases, ureteral injury can also happen. Sometimes, the newborn is also affected by these complications. There are chances of neonatal mortality and reduced foetal oxygen supply due to preterm birth.¹⁰

FAQs

How serious is placenta accreta?

Having placenta accreta makes the pregnancy a high risk. It might result in excessive bleeding before, during or after delivery, and patients might require a blood transfusion.

Can you survive placenta accreta?

Yes. If timely treatment is given, the patient can survive placenta accreta. Otherwise, it can turn life-threatening.

Can I have another baby after placenta accreta?

Yes. But, you will have an increased risk of preterm birth, maternal morbidity and placenta accreta spectrum in future pregnancies.

Which week will you deliver with placenta accreta?

With placenta accreta spectrum, delivery is usually done in 34-35 weeks of pregnancy. There are high chances of caesarean section delivery compared to vaginal delivery.

Summary

Placenta accreta spectrum is one of the several complications during pregnancy. It includes placenta accreta, placenta increta and placenta percreta. Placenta accreta refers to the placental attachment to less than 50% of the myometrium. Placenta increta refers to the placental attachment to more than 50% of the myometrium. Placenta percreta refers to the placental attachment to serosa and nearby organs. 

Vaginal bleeding in the third trimester is a sign of placenta accreta. Risk factors of placenta accreta include caesarean section, surgery of the endometrium, hysteroscopy, myomectomy, curettage, endometrial ablation, smoking, hypertension, placenta previa with history of c-section, in-vitro fertilisation or high maternal age.

Diagnosis is done by ultrasound, colour doppler or magnetic resonance imaging. Treatment depends on the severity of PAS, gestational age and condition of the patient. It can include a preterm delivery around 34-35 weeks of pregnancy, followed by peripartum hysterectomy. In some cases, the placenta is retained intentionally and left to absorb by necrosis. 

If timely treatment is not given, this condition can turn life-threatening.