Placenta Accreta Spectrum
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Direct answer
Placenta accreta spectrum describes abnormal adherence of placental tissue to the uterine wall, graded as accreta, increta and percreta by depth of invasion. Its strongest risk factor is a previous caesarean section, especially when placenta praevia coexists, and it causes life-threatening haemorrhage at delivery. Ultrasound with colour Doppler, supported by MRI, establishes the diagnosis, and planned delivery in a tertiary centre, often with caesarean hysterectomy, is the usual approach.
What you must remember
- Accreta: chorionic villi attach directly to the myometrium without an intervening decidua basalis.
- Increta: villi invade into the myometrium.
- Percreta: villi penetrate through the full myometrium to the serosa or adjacent organs such as the bladder.
- Risk factors: previous caesarean section, with risk rising with the number of scars, placenta praevia, prior uterine surgery and advanced maternal age.
- Imaging: ultrasound with grey-scale and colour Doppler, looking for placental lacunae, loss of the retroplacental clear zone and bladder wall interruption, with MRI for posterior or bladder involvement.
- Timing: planned late preterm delivery in a tertiary centre, commonly around 34 to 36 weeks, with a multidisciplinary team.
- Surgery: caesarean hysterectomy is the usual definitive approach, and manual removal of the placenta is avoided because it provokes bleeding.
A comparison of the three grades
A 34-year-old with two previous caesareans has an anterior low-lying placenta at 20 weeks. The depth of invasion decides the surgical plan, so the table grades the three types and their usual management side by side.
| Type | Depth of invasion | Usual management |
|---|---|---|
| Accreta | Attached to myometrium, no decidua | Planned surgery, uterus-sparing options only selectively |
| Increta | Invades into the myometrium | Caesarean hysterectomy usually, with blood on standby |
| Percreta | Through the uterine wall to serosa or adjacent organs | Multidisciplinary surgery, often with urological or general surgical input |
The depth of invasion explains both the bleeding and the need for other surgical teams. Conservative management with the placenta left in situ is an exception, and the role of methotrexate remains uncertain.
The plan for delivery, blood arrangements and surgical team roles should be documented early in pregnancy, well before the planned date. The team should also agree beforehand whether the placenta will be left in situ or the uterus removed.
Where the exam tries to catch you
Placenta accreta questions test the link between a caesarean scar, the dangerous manoeuvre to avoid and the need for planning.
- Trap: "Remove the placenta manually once the baby is out, as routine." Correct: manual removal in accreta provokes massive bleeding, so it is avoided.
- Trap: "Ultrasound is too insensitive, so skip imaging." Correct: ultrasound with Doppler and MRI are used to plan the surgery and the team.
- Trap: "Accreta can be managed like a normal anterior placenta praevia." Correct: a previous caesarean with anterior placenta praevia is high risk and needs a planned delivery.
Frequently asked questions
What is the difference between placenta accreta, increta and percreta?
Placenta accreta is attachment of chorionic villi directly to the myometrium without an intervening decidua, increta is invasion into the myometrium, and percreta is penetration through the full uterine wall. The depth of invasion determines the bleeding risk and surgical plan.
Why does a previous caesarean increase the risk of placenta accreta spectrum?
A previous caesarean section increases placenta accreta spectrum risk because the scar leaves a defect in the decidua, allowing trophoblast to invade the myometrium. Risk rises with the number of previous caesareans and is greatest when placenta praevia coexists.
Which imaging is used to diagnose placenta accreta spectrum?
Ultrasound with colour Doppler is the first-line imaging for placenta accreta spectrum, looking for placental lacunae and loss of the retroplacental clear zone. MRI is an adjunct when findings are unclear or when the posterior placenta or bladder may be involved.
Is manual removal of the placenta advised in placenta accreta?
Manual removal of the placenta is avoided in placenta accreta, since separating the invading placenta from the myometrium provokes massive haemorrhage. The usual approach is planned caesarean hysterectomy in a centre with blood products and multidisciplinary surgical support.