placenta percreta

**Definition / Spectrum (placenta accreta spectrum, PAS):** - Placenta accreta (~75-80%): villi attach to the myometrium, with no intervening decidua (absent decidua basalis / Nitabuch layer). - Placenta increta (~15%): villi invade INTO the myometrium. - Placenta percreta (~5%): villi invade THROUGH the myometrium and serosa (perforate), and may involve the bladder, parametria, bowel, or pelvic sidewall. - Mnemonic: accreta = "attaches," increta = "invades into," percreta = "perforates through."

**Pathophysiology:** - Defective or absent decidua basalis, usually at the site of a prior uterine scar (cesarean, myomectomy, curettage). This lets trophoblast invade abnormally deeply. - The placenta cannot separate in the third stage of labor. Attempts at manual removal or traction cause massive hemorrhage.

**Risk factors:** - Prior cesarean delivery. Risk rises with the number of cesareans. - Placenta previa. Previa plus a prior cesarean carries the highest risk. - Other uterine surgery (myomectomy, D&C), Asherman syndrome, advanced maternal age, multiparity, IVF.

**Clinical presentation:** - Often asymptomatic antenatally. It may present with painless vaginal bleeding in the third trimester if previa is present. - Intrapartum or postpartum: retained placenta and severe, life-threatening postpartum hemorrhage (PPH). - Percreta with bladder invasion can cause hematuria. Uterine rupture is also possible. - Elevated maternal serum AFP can be an incidental finding.

**Diagnosis:** - Prenatal ultrasound (first-line) with Doppler. Findings include loss of the normal hypoechoic retroplacental zone, placental lacunae ("Swiss cheese"), thinned myometrium, and bladder wall interruption with increased vascularity. - MRI is used as an adjunct when the diagnosis is uncertain or to assess depth and parametrial invasion. - Definitive diagnosis is by pathology or at delivery.

**Management:** - Planned preterm cesarean hysterectomy (typically 34-36 weeks) at a center with multidisciplinary expertise, with the placenta LEFT IN SITU (do not attempt to remove it). - Blood product availability and a massive transfusion protocol should be arranged. Urology involvement is needed if the bladder is involved. - Complications: hemorrhage, DIC, transfusion reactions, bladder/ureteral injury, infection, maternal death. - Conservative management (leaving the placenta in situ and uterus in place) is an option in select cases, with risks of delayed hemorrhage, infection, and DIC. Methotrexate has been used historically but has limited evidence. - Emergency (unplanned) delivery has much worse outcomes than planned delivery.

**Board pearls:** - Classic vignette: a multiparous woman with a prior cesarean and placenta previa has a retained placenta and heavy bleeding after delivery. The next step is hysterectomy. - Differential for third-stage hemorrhage with retained placenta: PAS vs. uterine atony (most common cause of PPH overall) vs. uterine inversion. - Histology: absence of decidua basalis, with villi directly adherent to or invading myometrium.