There are two major placental abnormalities. Placenta previa is a condition that occurs during pregnancy when the placenta is abnormally placed, and partially or totally covers the cervix.
Placental abruption occurs when the placenta separates from the wall of the uterus prior to the birth of the baby. This can result in severe, uncontrollable bleeding (hemorrhage).
The uterus is the muscular organ that contains the developing baby during pregnancy. The lowest segment of the uterus is a narrowed portion called the cervix. This cervix has an opening (the os) that leads into the vagina, or birthcanal. The placenta is the organ that attaches to the wall of the uterus during pregnancy. The placenta allows nutrients and oxygen from the mother's blood circulation to pass into the developing baby (the fetus) via the umbilicalcord.
During labor, the muscles of the uterus contract repeatedly. This allows thecervix to begin to grow thinner (called effacement) and more open (dilatation). Eventually, the cervix will become completely effaced and dilated, and thebaby can leave the uterus and enter the birth canal. Under normal circumstances, the baby will emerge through the mother's vagina during birth.
In placenta previa, the placenta develops in an abnormal location. Normally,the placenta should develop relatively high up in the uterus, on the front orback wall. In about 1 in 200 births, the placenta will be located low in theuterus, partially or totally covering the os. This causes particular problems in late pregnancy, when the lower part of the uterus begins to take on a new formation in preparation for delivery. As the cervix begins to efface and dilate, the attachments of the placenta to the uterus are damaged, resulting in bleeding.
During a normal labor and delivery, the baby is born first. Several minutes to 30 minutes later, the placenta separates from the wall of the uterus and isdelivered. This sequence is necessary because the baby relies on the placenta to provide oxygen until he or she begins to breathe independently.
Placental abruption occurs when the placenta separates from the uterus beforethe birth of the baby. Placental abruption occurs in about 1 out of every 200 deliveries. African American and Latin-American women have a greater risk of this complication than do Caucasian women. It was once believed that the risk of placental abruption increased in women who gave birth to many children,but this association is still being researched.
While the actual cause of placenta previa is unknown, certain factors increase the risk of a woman developing the condition. These factors include:
- Having abnormalities of the uterus
- Being older in age
- Having had other babies
- Having a prior delivery by cesarean section
- Smoking cigarettes.
When a pregnancy involves more than one baby (twins, triplets, etc.), the placenta will be considerably larger than for a single pregnancy. This also increases the chance of placenta previa.
Placenta previa may cause a number of problems. It is thought to be responsible for about 5% of all miscarriages. It frequently causes very light bleeding(spotting) early in pregnancy. Sometime after 28 weeks of pregnancy (most pregnancies last about 40 weeks), placenta previa can cause episodes of significant bleeding. Usually, the bleeding occurs suddenly and is bright red. The woman rarely experiences any accompanying pain, although about 10% of the timethe placenta may begin separating from the uterine wall (called abruptio placentae), resulting in pain. The bleeding usually stops on its own. About 25%of such patients will go into labor sometime in the next several days. Sometimes, placenta previa does not cause bleeding until labor has already begun.
Placenta previa puts both the mother and the fetus at high risk. The mother is at risk of severe and uncontrollable bleeding (hemorrhage), with dangerousblood loss. If the mother's bleeding is quite severe, this puts the fetus atrisk of becoming oxygen deprived. The fetus' only source of oxygen is the mother's blood. The mother's blood loss, coupled with certain changes that takeplace in response to that blood loss, decreases the amount of blood going tothe placenta, and ultimately to the fetus. Furthermore, placenta previa increases the risk of preterm labor, and the possibility that the baby will be delivered prematurely.
The cause of placental abruption is unknown. However, a number of risk factors have been identified. These factors include:
- Older age of the mother
- History of placental abruption during a previous pregnancy
- High blood pressure
- Certain disease states (diabetes, collagen vascular diseases)
- The presence of a type of uterine tumor called aleiomyoma
- Twins, triplets, or other multiple pregnancies
- Cigarette smoking
- Heavy alcohol use
- Cocaine use
- Malformations of the uterus
- Malformations of the placenta
- Injury to the abdomen (as might occur in a car accident).
Symptoms of placental abruption include bleeding from the vagina, severe painin the abdomen or back, and tenderness of the uterus. Depending on the severity of the bleeding, the mother may experience a drop in blood pressure, followed by symptoms of organ failure as her organs are deprived of oxygen. Sometimes, there is no visible vaginal bleeding. Instead, the bleeding is said tobe "concealed." In this case, the bleeding is trapped behind the placenta, orthere may be bleeding into the muscle of the uterus. Many patients will haveabnormal contractions of the uterus, particularly extremely hard, prolongedcontractions. Placental abruption can be total (in which case the fetus willalmost always die in the uterus), or partial.
Placental abruption can also cause a very serious complication called consumptive coagulopathy. A series of reactions begin that involve the elements of the blood responsible for clotting. These clotting elements are bound togetherand used up by these reactions. This increases the risk of uncontrollable bleeding and may contribute to severe bleeding from the uterus, as well as causing bleeding from other locations (nose, urinary tract, etc.).
Placental abruption is risky for both the mother and the fetus. It is dangerous for the mother because of blood loss, loss of clotting ability, and oxygendeprivation to her organs (especially the kidneys and heart). This conditionis dangerous for the fetus because of oxygen deprivation, too, since the mother's blood is the fetus' only source of oxygen. Because the abrupting placenta is attached to the umbilical cord, and the umbilical cord is an extensionof the fetus' circulatory system, the fetus is also at risk of hemorrhaging.The fetus may die from these stresses, or may be born with damage due to oxygen deprivation. If the abruption occurs well before the baby was due to be delivered, early delivery may cause the baby to suffer complications of premature birth.
Diagnosis of placenta previa is suspected whenever bright red, painless vaginal bleeding occurs during the course of a pregnancy. The diagnosis can be confirmed by performing an ultrasound examination. This will allow the location of the placenta to be evaluated.
While many conditions during pregnancy require a pelvic examination, in which the healthcare provider's fingers are inserted into the patient's vagina, such an examination should never be performed if there is any suspicionof placenta previa. Such an examination can disturb the already susceptible placenta, resulting in hemorrhage.
Sometimes placenta previa is found early in a pregnancy, during an ultrasoundexamination performed for another reason. In these cases, it is wise to havea repeat ultrasound performed later in pregnancy (during the last third of the pregnancy, called the third trimester). A large percentage of these womenwill have a low-lying placenta, but not a true placenta previa where some orall of the os is covered.
Diagnosis of placental abruption relies heavily on the patient's report of her symptoms and a the physical examination performed by a healthcare provider.Ultrasound can sometimes be used to diagnose an abruption, but there is a high rate of missed or incorrect diagnoses associated with this tool when usedfor this purpose. Blood will be taken from the mother and tested to evaluatethe possibility of life-threatening problems with the mother's clotting system.
Treatment of placenta previa depends on how far along in the pregnancy the bleeding occurs. When the pregnancy is less than 36 weeks along, the fetus is not sufficiently developed to allow delivery without a high risk of complications. Therefore, a woman with placenta previa is treated with bed rest, bloodtransfusions as necessary, and medications to prevent labor. After 36 weeks,the baby can be delivered via cesarean section. This is almost always the preferred method of delivery in order to avoid further bleeding from the low-lying placenta.
The first line of treatment for placental abruption involves replacing the mother's lost blood with blood transfusions and fluids given through a needle in a vein. Oxygen will be administered, usually by a mask or through tubes leading to the nose. When the placental separation is severe, treatment may require prompt delivery of the baby. However, delivery may be delayed when the placental separation is not as severe, and when the fetus is too immature to insure a healthy baby if delivered. The baby is delivered vaginally when possible. However, a cesarean section may be performed to deliver the baby more quickly if the abruption is quite severe or if the baby is in distress.
In cases of placenta previa, the prognosis for the mother is very good. The baby, however, has a 15-20% chance of dying. This is 10 times the death rate associated with normal pregnancies. About 60% of these deaths occur because the baby delivered was too premature to survive.
The prognosis for cases of placental abruption varies, depending on the severity of the abruption. The risk of death for the mother ranges up to 5%, usually due to severe blood loss, heart failure, and kidney failure. In cases of severe abruption, 50-80% of all fetuses die. Among those who survive, nearly half will have lifelong problems due to oxygen deprivation in the uterus and premature birth.
There are no known ways to insure the appropriate placement of the placenta in the uterus. However, careful treatment of the problem can result in the best chance for a good outcome for both mother and baby.
Some of the causes of placental abruption are preventable. These include cigarette smoking, alcohol abuse, and cocaine use. Other causes of abruption maynot be avoidable, like diabetes or high blood pressure. These diseases shouldbe carefully treated. Patients with conditions known to increase the risk ofplacental abruption should be carefully monitored for signs and symptoms ofthis complication.