Placenta accreta spectrum
|Placenta accreta spectrum|
|Other names||Placenta accreta, morbidly adherent placenta|
|Types of placenta accreta|
|Complications||Postpartum bleeding, disseminated intravascular coagulopathy, bladder injury|
|Types||Accreta, increta, percreta|
|Risk factors||Prior C-sections, high number of pregnancies, older age, uterine surgery, pelvic irradiation|
|Diagnostic method||Based on ultrasound|
|Treatment||C-section at 34 to 36 weeks, blood transfusion, hysterectomy|
|Frequency||1 in 272 pregnancies|
Placenta accreta is when the placenta attaches abnormally into the muscular layer of the uterine wall rather than just to the endometrium. The most common complication is postpartum bleeding, with other potential complications including disseminated intravascular coagulopathy (DIC) and bladder injury. The baby is also at higher risk of a poor outcome.
Risk factors include prior C-sections, a high number of prior pregnancies, older age, uterine surgery, and pelvic irradiation. Three grades of disease are defined by the depth of attachment into the muscular layers: accreta, increta, and percreta. In accreta chorionic villi attach to the myometrium, in increta they invade into the myometrium, while in percreta they invade to the outside of the uterus. Diagnosis is generally by ultrasound, though magnetic resonance imaging may occasionally be used.
Treatment often involve early delivery at 34 to 36 weeks via a C-section. Sufficient blood should be avaliable incase transfusion is required. If the placenta does not deliver, a hysterectomy is recommended though some techniques may be able to preserve fertility. Tranexamic acid may be used to try to decrease blood loss. Rates of placenta accreta have increased from the 1960s to the 2010s. As of 2016, they affect an estimated 1 in 272 pregnancies.
Signs and symptoms
- Damage to local organs (e.g., bowel, bladder,uterus and neurovascular structures in the retroperitoneum and lateral pelvic sidewalls from placental implantation and its removal;
- Postoperative bleeding requiring repeated surgery;
- Amniotic fluid embolism;
- Complications (such as dilutional coagulopathy, consumptive coagulopathy, acute transfusion reactions, transfusion-associated lung injury, acute respiratory distress syndrome, and electrolyte abnormalities) caused by transfusion of large volumes of blood products, crystalloids, and other volume expanders;
- Postoperative thromboembolism, infection, multisystem organ failure, and maternal death.
An important risk factor for placenta accreta is placenta previa in the presence of a uterine scar. Placenta previa is an independent risk factor for placenta accreta. Additional reported risk factors for placenta accreta include maternal age and multiparity, other prior uterine surgery, prior uterine curettage, uterine irradiation, endometrial ablation, Asherman syndrome, uterine leiomyomata, uterine anomalies, hypertensive disorders of pregnancy, and smoking.
The condition is increased in incidence by the presence of scar tissue i.e. Asherman's syndrome usually from past uterine surgery, especially from a past dilation and curettage, (which is used for many indications including miscarriage, termination, and postpartum hemorrhage), myomectomy, or caesarean section. A thin decidua can also be a contributing factor to such trophoblastic invasion. Some studies suggest that the rate of incidence is higher when the fetus is female. Other risk factors include low-lying placenta, anterior placenta, congenital or acquired uterine defects (such as uterine septa), leiomyoma, ectopic implantation of placenta (including cornual pregnancy).
Pregnant women above 35 years of age who have had a Caesarian section and now have a placenta previa overlying the uterine scar have a 40% chance of placenta accreta.
The placenta forms an abnormally firm and deep attachment to the uterine wall. There is absence of the decidua basalis and incomplete development of the Nitabuch's layer. There are three forms of placenta accreta, distinguishable by the depth of penetration.
|Placenta accreta||75–78%||The placenta attaches strongly to the myometrium, but does not penetrate it. This form of the condition accounts for around 75% of all cases.|
|Placenta increta||17%||Occurs when the placenta penetrates the myometrium.|
|Placenta percreta||5–7%||The highest-risk form of the condition occurs when the placenta penetrates the entire myometrium to the uterine serosa (invades through entire uterine wall). This variant can lead to the placenta attaching to other organs such as the rectum or urinary bladder.|
When the antepartum diagnosis of placenta accreta is made, it is usually based on ultrasound findings in the second or third trimester. Sonographic findings that may be suggestive of placenta accreta include:
- Loss of normal hypoechoic retroplacental zone
- Multiple vascular lacunae (irregular vascular spaces) within placenta, giving "Swiss cheese" appearance
- Blood vessels or placental tissue bridging uterine-placental margin, myometrial-bladder interface, or crossing the uterine serosa
- Retroplacental myometrial thickness of <1 mm
- Numerous coherent vessels visualized with 3-dimensional power Doppler in basal view
Unfortunately, the diagnosis is not easy and is affected by a significant interobserver variability. In doubtful cases it is possible to perform a nuclear magnetic resonance (MRI) of the pelvis, which has a very good sensitivity and specificity for this disorder. MRI findings associated with placenta accreta include dark T2 bands, bulging of the uterus, and loss of the dark T2 interface.
Although there are isolated case reports of placenta accreta being diagnosed in the first trimester or at the time of abortion <20 weeks' gestational age, the predictive value of first-trimester ultrasound for this diagnosis remains unknown. Women with a placenta previa or "low-lying placenta" overlying a uterine scar early in pregnancy should undergo follow-up imaging in the third trimester with attention to the potential presence of placenta accreta.
Treatment may be delivery by caesarean section and abdominal hysterectomy if placenta accreta is diagnosed before birth. Oxytocin and antibiotics are used for post-surgical management. When there is partially separated placenta with focal accreta, best option is removal of placenta. If it is important to save the woman's uterus (for future pregnancies) then resection around the placenta may be successful. Conservative treatment can also be uterus sparing but may not be as successful and has a higher risk of complications. Techniques include:
- Leaving the placenta in the uterus and curettage of uterus. Methotrexate has been used in this case.
- Intrauterine balloon catheterisation to compress blood vessels
- Embolisation of pelvic vessels
- Internal iliac artery ligation
- Bilateral uterine artery ligation
In cases where there is invasion of placental tissue and blood vessels into the bladder, it is treated in similar manner to abdominal pregnancy and manual placental removal is avoided. However, this may eventually need hysterectomy and/or partial cystectomy.
If the patient decides to proceed with a vaginal delivery, blood products for transfusion and an anesthesiologist are kept ready at delivery.
The reported incidence of placenta accreta has increased from approximately 0.8 per 1000 deliveries in the 1980s to 3 per 1000 deliveries in the past decade.
Incidence has been increasing with increased rates of Caesarean deliveries, with rates of 1 in 4,027 pregnancies in the 1970s, 1 in 2,510 in the 1980s, and 1 in 533 for 1982–2002. In 2002, ACOG estimated that incidence has increased 10-fold over the past 50 years. The risk of placenta accreta in future deliveries after Caesarian section is 0.4-0.8%. For patients with placenta previa, risk increases with number of previous Caesarean sections, with rates of 3%, 11%, 40%, 61%, and 67% for the first, second, third, fourth, and fifth or greater number of Caesarean sections.
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