Placenta accreta spectrum: Clinical sciences
Introduction0:00–1:10
The placenta accreta spectrum, known as PAS, refers to a range of abnormal placental invasion and adherence into the myometrial tissue of the uterus.
It occurs when there is an abnormal interface between the uterine endometrium and myometrium. This often occurs over a uterine scar, which is why placental trophoblasts anchor deeper than normal into the uterine wall.
The spectrum ranges from placenta accreta, where the placenta attaches to the myometrium; then, placenta increta, where invasion into the myometrium occurs; and placenta percreta, where the placenta penetrates through the myometrium and attaches to the uterine serosa; sometimes adjacent organs are also invaded, like the bladder.
PAS can be suspected antenatally, but sometimes isn’t discovered until after delivery, where life-threatening hemorrhage is often encountered when placental separation is attempted, due to this abnormally deep attachment.Your first step in evaluating a patient presenting with a chief concern suggesting PAS is to do a CABCDE assessment to determine if they are stable or unstable.
Unstable Patient1:10–4:41
Then, obtain IV access, and continuously monitor their vital signs. To confirm the diagnosis of PAS, you will need to obtain a focused history, physical exam, and labs including CBC, PT, INR, PTT, and fibrinogen.
Additionally, a uterine ultrasound performed at the bedside will help with diagnosis. However, don’t delay treatment while waiting for the diagnosis, since the hemorrhage can be life-threatening!
Others include myomectomy or dilation and curettage, also referred to as D&C. The risk of PAS increases after each uterine surgery, and PAS is a significant concern in those who have had multiple c-section births.
Additional risk factors for PAS include Asherman syndrome; multifetal pregnancy; advanced maternal age; and assisted reproductive technology such as in-vitro fertilization, or IVF.
On physical exam of an unstable patient, there is often profuse vaginal bleeding during attempted placental separation, and the placenta will feel adhered to the uterine wall.
Their vital signs will show hypotension and tachycardia, and they often experience altered mental status, look pale, and their skin will feel cold or clammy due to acute blood loss.
Labs may reveal low RBCs and platelets, elevated PT, PTT, and INR, and low fibrinogen as coagulation factors are consumed, but keep in mind that labs may not reflect the degree of blood loss as a hemorrhage can rapidly evolve and it takes time for lab values to reflect that.
Therefore, the patient’s clinical picture should serve as an indicator for transfusion rather than lab values. Additionally, a uterine ultrasound performed at the bedside frequently shows a hypervascular echogenic intrauterine mass suggesting retained placental tissue.
Based on these findings, you should diagnose PAS with postpartum hemorrhage and shock. Now, remember that PAS can cause life threatening hemorrhage, so you shouldn’t delay treatment while waiting for the definitive diagnosis.
In fact, while you’re getting your diagnosis, you’re still giving acute management. Continue to monitor your patient closely, provide aggressive IV fluid resuscitation, and prepare to give blood products.
Massive transfusion protocols can be utilized to ensure both packed red blood cells and clotting factors are replaced sufficiently.
If the patient isn’t already in the operating room, relocate there. If you have time, you can attempt a D&C to remove the placental tissue, particularly if there is only a small area that is stuck.
However, if bleeding persists or the placenta cannot be removed, quickly proceed with a hysterectomy. Okay, time to talk about stable patients who present before delivery.
Stable Patient4:41–7:05
When assessing stable antepartum patients, start with a focused history and physical exam. During the antenatal period, most patients with PAS will not have symptoms, but those with a coexisting placenta previa may present with painless vaginal bleeding in the second or third trimester.
Risk factors are the same as with unstable patients, with the biggest being a prior c-section birth. As a reminder, others include a history of myomectomy or D&C; Asherman syndrome; multifetal gestation; advanced maternal age; and assisted reproductive technology.
When it comes to the physical examination, it is often unremarkable.Here’s a clinical pearl! Although the patient’s physical examination often reveals no unusual findings, do not perform a digital cervical examination if your patient has a known placenta previa, or if the placenta’s location is unknown.If you suspect PAS, take a good look at the placenta when doing an ultrasound for fetal anatomic survey and be aware of the patient’s surgical history.
The most important finding is the presence of placenta previa in a patient with a history of a c-section birth. Here’s a high-yield fact!
Patients with a placenta previa found on antenatal ultrasound have a slightly increased risk of PAS compared to those without a previa.
However, if they have a placenta previa and a history of c-section birth, the risk of PAS essentially doubles and continues to increase as the number of c-section births increase.Okay, back to the ultrasound.
Additional findings of PAS include multiple placental vascular lacunae; loss of the normal hypoechoic zone between the placenta and myometrium known as the placenta clear zone; and retroplacental myometrial thinning.
These ultrasound findings are significantly more relevant in patients with a history of previous c-section birth, compared to those with no prior uterine surgeries.In some cases, the placenta may be seen invading the myometrium, uterine serosa, or even through the serosa and into the bladder.If you see these unique ultrasound findings, expect placenta accreta spectrum.
Expected PAS 7:05–9:24
With the diagnosis made, the key is preparation. Delivering a patient with expected PAS requires a multidisciplinary team of obstetric, anesthesia, critical care, and surgical personnel experienced in managing substantial complications.
It should happen in a facility that has a 24-hour blood bank with massive transfusion protocol capability and has both a neonatal and adult ICU.
You should anticipate severe hemorrhage at delivery, so optimize maternal hemoglobin throughout the pregnancy and consider giving intravenous iron in the third trimester if your patient is anemic.
Delivery should occur in the late preterm period, so consider antenatal steroids prior to planned delivery between 34 weeks and 35 weeks, and 6 days.
At the time of surgery, be sure to place two large bore IVs, cross-match for blood products, and consider having an autologous cell saver.
Depending on how deep the placental invasion appears, ureteral stents can be inserted for intraoperative identification, and iliac artery balloons can be placed to decrease blood flow to the uterus to limit blood loss.
Antifibrinolytic therapy with tranexamic acid, or TXA, may also be used to decrease blood loss. Generally, management of expected PAS is to perform a cesarean hysterectomy if the placenta does not spontaneously separate after delivery of the fetus.
Do not attempt to force removal as this can cause bleeding! Instead, keep the placenta in place, rapidly close the uterus, and proceed with a hysterectomy.
Here’s a clinical pearl! In very specific and rare cases, you can consider excising the adherent placenta and a portion of the uterine wall, then repairing the defect, or you can ligate the cord near the placenta and close the uterus.
This may allow for a delayed hysterectomy, which is usually less risky and has lower blood loss compared to a cesarean hysterectomy.
Unexpected PAS 9:24–10:55
In this case, they receive routine antepartum care and delivery planning. During the physical exam after delivery, you might notice profuse vaginal bleeding as the placenta starts to separate.
There might be a lack of a cleavage plane between the placenta and uterine wall, making the placenta firmly adherent despite traction on the cord.
Additionally, if part of the placenta is retained in the uterus, you might find that it is incomplete during your post-delivery inspection.With these findings, you would strongly suspect PAS, so perform a bedside ultrasound.
If you see a hypervascular echogenic intrauterine mass consistent with retained placental tissue, that is unexpected PAS.
Keep in mind that PAS puts them at risk of severe and potentially life-threatening hemorrhage. In fact, even if your patient is stable at the moment, they are often bleeding heavily, so be sure to closely monitor the patient’s vital signs.
Start IV fluid resuscitation and if there’s evidence of evolving shock provide blood products. The bleeding usually persists until the placenta is completely removed, so if you are not already in the operating room, relocate there.
You can start with a D&C to remove the placenta, but if bleeding persists or the patient becomes unstable, you should proceed with a hysterectomy.
Alright, as a quick recap… The placenta accreta spectrum refers to a range of abnormal placental invasion and adherence into the myometrial tissue of the uterus.
Review10:55–11:59
Unstable patients with PAS should receive resuscitation with IV fluids and blood products while proceeding to the OR for possible D&C or hysterectomy.
When it comes to stable patients, the best way to diagnose PAS antenatally is with ultrasound in the setting of risk factors.
If PAS is expected, start by optimizing maternal hemoglobin, forming a multidisciplinary delivery team, and preparing for delivery in the late preterm period.
With expected PAS, you should have blood products, a cell saver, ureteral stents, iliac balloons, and TXA available at delivery, as the risk for hemorrhage is high.
For patients who have unexpected PAS at delivery, maintain stabilization with fluids and blood products while relocating to the OR for a D&C or possible hysterectomy.
- "Obstetric care consensus no. 7: Placenta accreta spectrum" Obstet Gynecol (2018)
- "Placenta Accreta Spectrum" Obstet Gynecol (2023)
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