Placenta accreta spectrum

Definition

• Placenta accreta spectrum comprises disorders of placentation with abnormal invasion of trophoblast into the myometrium.

Classification

Terms

• Placenta accreta means villi attaching directly to the myometrium because decidua is missing.
• Increta means growth into the myometrium, and percreta growth through the serosa, possibly involving bladder or parametria.
• The strongest risk factor is the combination of placenta praevia and previous caesarean, rising with the number of caesareans.

• By depth of invasion, the following are distinguished: placenta accreta (villi attach directly to the myometrium in the absence of decidua), increta (villi penetrate deeply into the myometrium) and percreta (villi reach or penetrate the serosa).
• FIGO has proposed a grading system under the umbrella term PAS that replaces the previous categorical terminology.

Occurrence & epidemiology

Epidemiology

• Its frequency has increased with the rising caesarean section rate; a US database study found placenta accreta in 1 in 272 births between 1998 and 2011.

Aetiopathogenesis

Aetiology and risk factors

• The main risk factor is previous caesarean section combined with placenta praevia; with placenta praevia the risk rises with the number of caesarean sections from 3% (none) through 11%, 40% and 61% to 67% (four or more).

Clinical features

Clinical features and complications

• PAS is associated with increased maternal morbidity and mortality; after birth of the baby the placenta often does not separate within 30 minutes, and attempts at separation typically cause massive haemorrhage.

Diagnosis

Ultrasound signs

• Typical are loss of the retroplacental clear zone, placental lacunae ("Swiss cheese"), thinning of the myometrium and interruption of the bladder wall line.
• On colour Doppler you see hypervascularity at the uterovesical interface and bridging vessels between placenta and surroundings.
• MRI is considered for a posterior placenta, unclear ultrasound findings and assessment of the extent.

• MRI has high sensitivity and specificity but has not so far proved superior to ultrasound; it is used mainly when ultrasound findings are inconclusive.

Keep learning in the app

Further reading (selection)

1. StatPearls: Placenta Accreta (NCBI Bookshelf)
2. MSD Manual Professional Edition: Placenta Accreta
3. DocCheck Flexikon, Placenta accreta

Cross-references