B3. Placenta accreta, increta and percreta

The placenta accreta spectrum (PAS) disorders, also called abnormally invasive placenta (AIP) or placentation abnormalities, are a group of disorders where the placenta invades deeper into the uterine wall than normal. The three disorders are:

• Placenta accreta – (80%) – the placenta extends to the myometrium and attaches to it
• Placenta increta – (15%) – the placenta invades through the entire thickness of the myometrium
• Placenta percreta – (5%) – the placenta invades through the entire uterine wall, including the serosa or neighbouring organs

The problem with these disorders is that the placenta in these cases does not detach spontaneously or completely, which can cause life-threatening postpartum haemorrhage. It also increases the risk for abnormal foetal lie and premature labour.

It occurs in approx. 3 – 5 / 10 000 births.

Etiology

• Procedures causing defects in the uterine wall
  • Previous C-section
  • Previous curettage
  • Previous myomectomy
• Placenta praevia

Clinical features

These disorders are often asymptomatic and are therefore unnoticed (unless detected during screening) until the third stage of labour, at which time the placenta won’t spontaneously separate. As is routine, the clinician may attempt to manually separate it, which will either prove difficult or cause severe bleeding.

They may also cause abnormal uterine bleeding antepartum. If placenta percreta penetrates into the bladder, it may cause haematuria.

Diagnosis and evaluation

Placenta accreta spectrum disorders, especially the more severe ones, are usually discovered during routine antenatal ultrasound screening. Placenta accreta itself is not as visible on ultrasound and is often diagnosed postpartum.

In most pregnant women, normal placentation is visible and so PAS disorders can be ruled out. However, if abnormal placentation cannot be ruled out during routine antenatal ultrasound screening, the patient should return a few weeks later for repeat ultrasound. At a gestational age of 18 – 24 weeks, PAS can be ruled in or out with 90% accuracy. MRI can be used if the diagnosis with ultrasound is unclear.

Because placenta praevia is associated with PAS, patients with diagnosed placenta praevia should have an extra ultrasound control for PAS later in the pregnancy.

Treatment

Patients with antenatally diagnosed placenta increta or percreta are scheduled for early delivery (weeks 34 – 36) with C-section and hysterectomy. Rather than trying to separate the placenta from the uterus, the uterus is removed altogether with the placenta left in place.

Unexpected placenta accreta spectrum disorder, usually suspected after vaginal birth due to severe bleeding and lack of placental separation, requires hysterectomy.