|Classification and external resources|
Types of placenta accreta
Placenta accreta is a severe obstetric complication involving an abnormally deep attachment of the placenta to the myometrium (the middle, muscular layer of the uterine wall), without penetrating it. Thus, the placenta grows completely through the endometrium.
The placenta usually detaches from the uterine wall relatively easily, but women who encounter placenta accreta during childbirth are at great risk of hemorrhage during its removal. This commonly requires surgery to stem the bleeding and fully remove the placenta, and in severe forms can often lead to a hysterectomy or be fatal.
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 hemorrhaging), 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).
The placenta forms an abnormally firm 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 worst form of the condition is 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 bladder.|
Signs and symptoms
There can be recurrent vaginal spotting and overt hemorrhages. These symptoms and signs are not specific to the condition itself and are commonly seen in different obstetric conditions.
Myometrial invasion by placental villi at site of scar of previous caesarian section can lead to uterine rupture before labor, as early as 12 weeks.
Placenta accreta is very rarely recognised before birth, and is very difficult to diagnose. A Doppler ultrasound can lead to the diagnosis of a suspected accreta and an MRI will give more detail leading to further suspicion of such an abnormal placenta. However, both the ultrasound and the MRI rarely confirm an accreta with certainty. While it can lead to some vaginal bleeding during the third trimester, this is more commonly associated with the factors leading to the condition. In some cases the second trimester can see elevated maternal serum alpha-fetoprotein levels, though this is also an indicator of many other conditions. A three-dimensional power color doppler ultrasound scan has been used with good detection rates (PPV 87.5%).
During birth, placenta accreta is suspected if the placenta has not been delivered within 30 minutes of the birth. Usually in this case, manual blunt dissection or placenta traction is attempted but can cause hemorrhage in accreta.
Sometimes, placenta accreta invades bladder. Can also cause excessive hemorrhage as placenta rips myometrium during birth leading to bleeding from spiral arteries.
The safest and most common treatment is a planned caesarean section and abdominal hysterectomy if placenta accreta is diagnosed before birth. Pitocin and antibiotics are used for post-surgical management. When there is partially separated placenta with focal accreta, best option is removal of placenta and oversewing the uterine defect. 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, but there is no consensus whether this therapy is any more effective than observation.
- 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 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.
Placenta accreta affects approximately 1 in 533 pregnancies. The risk of placenta accreta in future deliveries after caesarian section is 0.4-0.8%. It occurs in 15% of patients with placenta previa. Patients above 35 years of age, who have had placenta previa and also a caesarian section have 40% chance of placenta accreta. In patients with placenta previa and multiple caesarian sections, the risk is 60-65%. In 2002, ACOG estimated that incidence has increased 10-fold over the past 50 years.
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- Interactive graphic explaining placenta accreta / Stanford Medical School Magazine article (right side)