Normally, the placenta will have a naturally occurring cleavage plane that separates it from the uterine wall. This allows for easy removal or expulsion of the placenta following a delivery either vaginally or by cesarean section.
In roughly one out of 2500 to as many as one of 500 plus pregnancies, the placenta will attach itself to the uterine wall, and will not be easily removed as is normally the case. There are different levels of penetration by the placenta into the uterine wall. A placenta accreta will have an absent cleavage plane, but will not pentrate into the uterine muscle. If the placenta penetrates into the uterine muscle (myometrium), the condition is known as a placenta increta. In fewer cases, the placenta will penetrate all the way through the uterine wall, and this condition is known as placenta percreta. The placenta percreta may even invade structures located close to the uterus like the urinary bladder.
Placenta accreta has a higher incidence of occurrence in patients who have had a previous cesarean section or who have a placenta previa. The exact reason for a placenta accreta, however, is unknown. Vaginal bleeding in the third trimester can be suggestive of a placenta accreta. The medical provider will most likely get an ultrasound to look for the cause of the bleeding, and oftentimes the placenta accreta will be diagnosed at this time. An MRI can also be performed to help diagnose placenta accreta if the ultrasound is inconclusive. Sometimes, however, the placenta accreta is discovered at the time of delivery.
Placenta accreta carries certain risks. One is premature delivery of the infant. Your provider will most likely recommend bed rest and pelvic rest to help minimize the bleeding. A course of betamethasone may be suggested as well to accelerate the fetal lung maturity. Weekly or twice weekly nonstress tests will be administered to make sure that the infant is healthy. Biophysical profiles will also be done on a weekly basis to check for fetal well being. Fetal compromise or heavy vaginal bleeding may force your provider to deliver the infant early. Your provider will most likely elect to transfer your care to a tertiary care facility due to this potentially life threatening condition. Usually, the infant is delivered electively at 34 weeks gestation after receiving steroids and without performing an amniocentesis to document fetal lung maturity.
There is also the risk of heavy uterine bleeding due to the inability to remove the placenta from the uterine wall. In the worst case scenario, this may lead to a hysterectomy. Depending on the severity of the uterine bleeding, your provider may elect to ligate the uterine arteries or the hypogastric arteries. Tying off these arteries will not compromise the uterus later as follow up imaging studies show that the arteries regain their patency over time. Using an intrauterine balloon to tamponade the bleeding is also a possibility. Embolization of the pelvic vessels by an interventional radiologist is another treatment modality. The American College of Obstetricians and Gynecologists (ACOG) recommend a planned cesarean section and hysterectomy at the time of delivery at 34 weeks as the College feels that trying to remove the placenta accreta will lead to severe uterine bleeding. The placenta is left attached to the uterus during this process. The College does state, however, that management of the placenta accreta may be individualized. Ultimately, the recommended treatment of choice for this condition, according to ACOG, is hysterectomy.
Typically, the placenta accreta is managed by a team of different specialists at the time of delivery including, but not limited to, the obstetrician, urologist, gynecologic oncologist, and an interventional radiologist. Blood will most likely be typed and crossed and ready for immediate transfusion of necessary along with other blood products. Depending on the severity of the bleeding, the patient may be followed in the intensive care unit postoperatively.
If you have been diagnosed with a placenta accreta, discuss your options carefully with your provider(s). Wishing you a successful, and problem free delivery. Feel free to leave comments or questions. Pablo