Placenta Accreta Spectrum
A 35-year-old woman with three previous cesarean sections is admitted at 37 weeks for elective repeat cesarean section. Antenatal ultrasound showed an anterior low-lying placenta with multiple lacunae and loss of the clear zone. At surgery the placenta is densely adherent to the uterine wall without invading the myometrium or bladder. Which of the following is the most likely diagnosis?
- A.Placenta accretaCorrect
- B.Placenta increta
- C.Placenta percreta
- D.Placenta previa
Explanation
Placenta accreta spectrum describes abnormally adherent or invasive placentation caused by a deficient decidua basalis, typically over a previous uterine scar, so that chorionic villi attach directly to or invade the myometrium. The depth of invasion defines the terminology: accreta means villi adhere to the myometrial surface without invading it, increta means villi invade into the myometrium, and percreta means villi penetrate the full thickness of the serosa and may involve the bladder or bowel. Here the placenta is densely adherent without myometrial invasion or bladder involvement, which is accreta, the commonest form, accounting for about 75 percent of cases. The two dominant risk factors are previous cesarean section and placenta previa, and their combination is multiplicative: with previa and three prior cesareans the risk approaches 40 percent. The sonographic features described, multiple placental lacunae giving a moth-eaten appearance and loss of the retroplacental clear zone, are classic, and MRI can add information for posterior or ambiguous cases. Placenta previa alone means the placenta covers or lies close to the internal os and describes position rather than adherence, so it does not explain dense adherence to the uterine wall. Recognition before delivery is critical, since planned delivery at 34 to 36 weeks in a center with an experienced multidisciplinary team, blood products, and cell salvage, usually with cesarean hysterectomy leaving the placenta in situ, markedly reduces hemorrhage and mortality.
Why each option
- A.
- Correct. Dense adherence to the uterine wall without invasion into the myometrium defines accreta, the commonest form of the spectrum.
- B.
- Increta implies villous invasion into the myometrium itself, which is explicitly absent in this description.
- C.
- Percreta means penetration through the full uterine wall and serosa, often involving the bladder, which is not present here.
- D.
- Placenta previa describes placental position over or near the internal os and is a risk factor for accreta, but it does not itself cause abnormal adherence.
Reference: ACOG Obstetric Care Consensus No. 7, Placenta Accreta Spectrum, reaffirmed 2023; RCOG Green-top Guideline No. 27a, 2018
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