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One serious complication that may occur

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in the context of pregnancy is abnormal

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placentation or placenta accreta spectrum.

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Placenta accreta spectrum is a spectrum

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of abnormal relationships between

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the chorionic villi of the placenta

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and the uterine muscle or myometrium.

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Patients at risk for placenta accreta

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spectrum are patients who have had any

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type of trauma to the uterus that would

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interrupt or scar the uterine decidua.

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The decidua is an important structure

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in determining how far the chorionic

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villi of the placenta will travel

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when the placenta is developing.

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And there are chemical signals within the

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decidua that provide feedback to the placental

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cells to tell them when to stop migrating.

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So an absent or abnormal decidual layer

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will place the patient at increased

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risk of abnormal placentation.

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These risk factors include prior cesarean

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section, prior dilation and curettage

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of the uterus, and assisted reproductive

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technologies, including in vitro fertilization.

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Advanced maternal age and multiparity are

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also considered risk factors for placenta

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accreta spectrum, largely because patients who

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are older may have had prior pregnancies and

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because multiparity also places patients at

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greater risk for having a cesarean section.

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Within the spectrum of placenta accreta,

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we can further classify this condition

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into three different categories.

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Placenta accreta is an abnormal attachment

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of the placenta to the uterine decidua

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with abutment of the uterine myometrium.

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Placenta percreta is invasion of

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the placenta into the muscular

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layer of the uterus, the myometrium.

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And then placenta percreta is extension

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of placental tissue to or beyond

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the level of the uterine serosa,

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with the potential to invade structures in the

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pelvis adjacent to the site of uterine breach.

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A handy mnemonic that I like to use to remember

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these three classifications is that accreta

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is attachment, so abnormal attachment of

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the placenta to the decidua and myometrium.

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Increta is invasion of the myometrium by

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the placenta, and percreta is perforation of

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the uterine serosa by the placental tissue.

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Many patients with placenta

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accreta spectrum

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will also have placenta previa, which is

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a low-lying placenta that partially or

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completely covers the internal cervical os.

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We can see in this diagram that this patient

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indeed has a diagnosis of previa, with the

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placenta covering the internal cervical os.

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This patient also has placenta percreta, with

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a focal placental bulge extending outside

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of the uterus and toward the bladder dome.

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The reason that many patients with PAS

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will also have placenta previa is because

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that scarring that can act as an abnormal

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point of attachment for the placenta often

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occurs at the site of a prior cesarean

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section scar, which is intrinsically

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in the low uterine segment anteriorly.

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So that scarring will often lead to tethering

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of the uterus and a concomitant placenta previa.

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Identifying placenta accreta spectrum is

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critical to caring for this patient population.

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Because placenta accreta spectrum significantly

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increases the risk of peripartum hemorrhage.

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This is because when the placental cells

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move into the uterus during normal placental

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migration, they are remodeling and enlarging

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maternal blood vessels, including arteries.

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And so, in addition to the large volume of

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maternal blood that's circulating in the

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context of pregnancy, the placenta is also

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carrying a significant volume of blood.

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In patients with placenta accreta spectrum,

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we can also see aberrant vasculature.

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And so these patients are at significant

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risk of bleeding in the peripartum period.

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Because patients with placenta accreta

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spectrum undergo planned cesarean delivery,

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typically at 30 to 34 weeks gestation,

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there is also a significant risk of both

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maternal and fetal morbidity and mortality

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because of that premature delivery.

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And then finally, patients with placenta

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accreta spectrum are at increased risk of

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infection if the placenta is incompletely

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removed at the time of delivery.

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Management of placenta accreta spectrum

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is largely surgical, and goals of

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care for these patients center

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around creating a safe delivery plan.

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It is absolutely essential to have a

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multidisciplinary care team that's taking

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part in the management of these patients.

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And that includes OBGYN and maternal fetal

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medicine, occasionally gynecologic oncology from

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a surgical perspective, urology, interventional

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radiology, diagnostic radiology, and OR nursing.

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It's a big team.

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Operative planning for these patients

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includes review of the imaging, particularly

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if placenta percreta is suspected.

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The ultimate goal of the multidisciplinary

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care team is to decrease the

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risk of peripartum hemorrhage.

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And so we may end up doing preoperative CTA

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or MRA for these patients if indicated for

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operative planning, although this is rare.

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And then patients may also undergo

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uterine artery embolization.

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So, as I mentioned, delivery is

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planned at 30 to 34 weeks gestation.

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Typically, patients, particularly with

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placenta percreta, will undergo a midline

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abdominal incision and then a transfundal

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uterine incision, rather than the low anterior

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incision that's classic for cesarean section.

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The fetus is delivered breech,

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and then the uterus is oversewn.

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If the patient is going to undergo uterine

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artery embolization, it happens at this time,

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after the fetus is delivered and

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after the uterus has been oversewn.

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After uterine artery embolization,

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patients with placenta percreta and

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sometimes advanced cases of accreta

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and increta will undergo hysterectomy.

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The approach of the surgery is largely

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dictated by the amount of vasculature

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that has been recruited by the placenta.

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So if there is significant vascular recruitment

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in a case of percreta, the surgeons may

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have to perform a radical hysterectomy

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rather than a standard hysterectomy.

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In that case, they would take a more

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lateral and extensive vascular pedicle.