Interactive Transcript
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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.
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