The placenta is one of the most important parts of a pregnant woman’s body. Via the umbilical cord, it provides the oxygen and nutrients to the growing baby inside the womb, and it removes waste products from the baby’s bloodstream. During a normal pregnancy, the placenta attaches itself to the uterine wall, where it remains until after the baby is born, at which time it detaches.
When placenta accreta occurs, however, the placenta attaches itself too deeply, entangling its tissue and blood vessels in the uterine wall. This happens in perhaps one out of every 500 pregnancies. The various forms of placenta accreta are categorized according to their severity; placenta increta is when the placenta grows deeply enough into the uterus to become attached to the uterine muscle (this occurs in 15 percent of all cases of accreta). In cases of placenta percreta, the placenta penetrates the uterine wall entirely and can even invade nearby organs such as the bladder. Placenta percreta occurs in approximately 5 percent of cases of placenta accreta.
Symptoms of Placenta Accreta
Placenta accreta often presents no symptoms at all, although there can be some vaginal bleeding during the third trimester or during labor.
Causes of Placenta Accreta
Although the cause of placenta accreta is not entirely clear, some people believe placenta accreta is more likely if the patient has had previous cesarean deliveries, possibly because the placenta may attach to the site of a C-section scar, where the uterine lining that would normally prevent placenta accreta has been compromised. Note that placenta accreta can also occur even with no history of C-section, and prior myomectomy (fibroid removal) surgery can also be a risk factor if the uterine lining was involved.
The chance of having placenta accreta increases with each C-section. Researchers have noted an increase in cases of placenta accreta (a tenfold increase over the last fifty years, according to some sources) as cesarean deliveries have become more common, and more than 60 percent of cases of placenta accreta occur in women who have had multiple cesarean deliveries, according to the American Pregnancy Association.
As noted above, previous uterine surgery is the most important risk factor for placenta accreta. Other risk factors include:
- The mother’s age (placenta accreta is more common in women over the age of 35)
- Placenta previa, a condition in which the placenta partially or completely covers the cervix (placenta accreta happens to 5–10 percent of all women who have placenta previa)
- Previous pregnancies
- Mother carrying twins or multiples
- Abnormal conditions in the uterus such as uterine fibroids, or the scar tissue that may be seen with Asherman’s syndrome
Complications of Placenta Accreta
There are numerous risks associated with placenta accreta. Hemorrhaging can occur during manual attempts to detach the placenta, and if the hemorrhaging is severe enough it can lead to death. There is also a risk of damaging the uterus and other organs during the removal of the placenta.
For the baby, premature delivery is the primary concern. For the mother, there is the above-mentioned danger of excessive bleeding, which in some cases can lead to disseminated intravascular coagulopathy (DIC), a potentially life-threatening condition in which the blood begins to clot abnormally, creating blockage in smaller blood vessels throughout the body. In cases of placenta percreta, there is a danger that other organs may be damaged in the course of removing the placenta.
The tool most commonly used to diagnose placenta accreta is ultrasound, although in some cases doctors prefer magnetic resonance imaging (MRI).
If your doctor suspects placenta accreta, he or she may also take a blood sample from you to test for elevated levels of a protein known as alpha fetoprotein. This protein is produced by the baby, and inordinately high levels of it in your bloodstream may indicate placenta accreta.
It is rare for this diagnosis to be made prior to the delivery, and further, if the diagnosis is made during the pregnancy it is often wrong. This rare condition is normally not diagnosed until the delivery itself takes place, and then either hemorrhage occurs or the placenta cannot be easily removed.
Unfortunately, hysterectomies are the most common intervention. Even more unfortunate is that there is nothing that can be done to prevent placenta accreta or treat it once it has been diagnosed. Most healthcare professionals will monitor the expectant mother very closely for the remainder of her pregnancy to ensure that no further complications arise.
Ironically, considering their suspected role in causing placenta accreta, C-section deliveries—followed by hysterectomy—are often necessary. In some cases doctors prefer to schedule these procedures as early as the 35th week of pregnancy in order to avoid having to deal with the baby’s birth on an emergency basis. In cases in which hysterectomy is avoidable, subsequent pregnancies will be at elevated risk for miscarriage, preterm delivery, or recurrence of placenta accreta.