None — The Placenta
The placenta is a flat, circular-shaped organ that attaches to the inside wall of the uterus during pregnancy. The baby is connected to the placenta through the umbilical cord. By birth, the placenta weighs about one pound.
The placenta is rich in blood vessels from the mother and serves as the storehouse for the fetus. Fetal blood travels through the umbilical cord to the placenta, where nutrients and oxygen are exchanged for the baby's waste products. This exchange takes place very efficiently, even though the maternal and fetal blood supplies normally don't mix. The baby's waste products are carried into the mom's circulatory system and processed by the kidneys for disposal. The placenta also produces important hormones during pregnancy, like chorionic gonadotropin (hCG), estrogen, progesterone and relaxin.
Placenta Accreta
Placenta accreta is an abnormal condition in which the placenta attaches too deep into the uterine wall. Abdulla Al-Khan, M.D., Obstetric Surgeon with Hackensack University Medical Center in Hackensack, NJ, compares the condition to invasive cancer because the placental cells can continue to grow and invade the tissue. In the second stage, called placenta increta, the placenta invades the muscle and attaches deep inside the muscle wall. The third stage, placenta percreta, is very serious. The placenta penetrates through the uterine wall and can attach to other organs in the abdominal cavity, particularly the bladder.
According to the American Pregnancy Association, placenta accreta and its related conditions occurs in about one out of every 2,500 pregnancies. Placenta accreta is the most common, accounting for about 75 percent of cases. Placenta increta occurs in 15 percent of cases. Researchers don't know the exact cause for the abnormal placental growth and attachment. However, the condition is more common in women who have had a prior c-section and/or a pregnancy with placenta previa, in which the placenta lies too low and covers part or all of the cervix. Al-Khan says it appears the scar tissue from the c-section disrupts the natural barrier that prevents the placenta from going beyond the uterine wall.
Dealing with Placental Invasion
Al-Khan says the baby is usually not harmed by placenta accreta. However, the risk for the mom is very high. Because the placenta has invaded so deeply, it doesn't readily separate from the uterine wall after delivery. The placenta, which is full of blood vessels from the mom, can be torn or damaged, causing severe hemorrhaging. In fact, Al-Khan says hemorrhaging is now the leading cause of maternal death in the U.S.
Planning is important to protect the health of the mom after delivery. Al-Khan says doctors can use high-tech Doppler ultrasound or MRI scans to diagnose placenta accreta in women who may be at risk for the condition (because of previous c-sections, history of placenta previa or bleeding during pregnancy). If the diagnosis is confirmed, he likes to deliver the baby around 34 weeks. Early delivery enables him to have a trained team of medical staff on hand to deal with any complications in the mom or baby.
Delivery is performed through a c-section. But instead of the usual horizontal incision, Al-Khan uses a long vertical incision in the stomach. He says this type of incision is needed to be able to clearly see the uterus and the full extent of the placental attachment. Once the baby is delivered, the blood is drained from the umbilical cord and it is tied it off at the base. The uterus (with the placenta still attached) is then stitched closed.
About three days later, surgeons use X-rays to locate the extra blood vessels made by the placenta. A catheter is inserted into the circulatory system and fed up to the extra vessels in the pelvis. Those vessels are then blocked (embolized) to prevent blood from leaking out. After two to three weeks, if the patient shows no signs of bleeding or infection, a hysterectomy is done. Al-Khan says if the placenta has not breached the muscle wall (i.e., hasn't reached the second stage, or placenta increta), it's possible for a woman to avoid a hysterectomy.
For general information on placenta accrete and other pregnancy-related conditions: