Vaginal Bleeding During Late Pregnancy
During late pregnancy (after 20 weeks), 3 to 4% of women have vaginal bleeding. Such women are at risk of losing the baby or of bleeding excessively (hemorrhaging). Sometimes so much blood is lost that blood pressure becomes dangerously low (causing shock) or small blood clots form throughout the bloodstream (called disseminated intravascular coagulation).
The most common cause of bleeding during late pregnancy is
Usually, labor starts with a small discharge of blood mixed with mucus from the vagina. This discharge, called the bloody show, occurs when small veins are torn as the cervix begins to open (dilate), enabling the fetus to pass through the vagina. The amount of blood in the discharge is small.
More serious but less common causes (see Table: Some Causes and Features of Vaginal Bleeding During Late Pregnancy) include
In placental abruption, the placenta detaches from the uterus too soon. What causes this detachment is unclear, but it may occur because blood flow to the placenta is inadequate. Sometimes the placenta detaches after an injury, as may occur in a car crash. Bleeding may be more severe than it appears because some or most of the blood may be trapped behind the placenta and thus not be visible. Placental abruption is the most common life-threatening cause of bleeding during late pregnancy, accounting for about 30% of cases. Placental abruption may occur at any time but is most common during the 3rd trimester.
In placenta previa, the placenta is attached to the lower rather than the upper part of the uterus. When the placenta is lower in the uterus, it may partly or completely block the cervix (the lower part of the uterus), which the fetus must pass through. Bleeding may occur without warning, or it may be triggered when a practitioner examines the cervix to determine whether it is dilating or whether labor has started. Placenta previa accounts for about 20% of bleeding during late pregnancy and is most common during the 3rd trimester. It may occur during early pregnancy, but the placenta usually moves out of the way on its own before delivery.
In vasa previa, the blood vessels that provide blood to the fetus (through the umbilical cord) grow across the cervix, blocking the fetus's passageway. When labor starts, these small blood vessels may be torn, depriving the fetus of blood. Because the fetus has a relatively small amount of blood, loss of even a small amount can be serious, and the fetus may die.
Rupture of the uterus may occur during labor. It almost always occurs in women whose uterus has been damaged and contains scar tissue. Such damage may occur during a cesarean delivery or surgery or result from an infection or a severe abdominal injury.
Bleeding may also result from disorders unrelated to pregnancy.
Various conditions (risk factors) increase the risk of disorders that can cause bleeding during late pregnancy.
For placental abruption, risk factors include
For placenta previa, risk factors include
For vasa previa, risk factors include
For rupture of the uterus, risk factors include
Doctors focus on ruling out potentially serious causes of bleeding (such as placental abruption, placenta previa, vasa previa, and rupture of the uterus). If the evaluation rules out these more serious causes, doctors usually diagnose the most common cause—the start of labor, indicated by the bloody show.
Any vaginal bleeding late during pregnancy is considered a warning sign, except for the bloody show, which is only a small amount of blood mixed with mucus and which does not last long.
Doctors are particularly concerned about women with fainting, light-headedness, or a racing heart—symptoms that suggest very low blood pressure.
A woman with vaginal bleeding late during pregnancy should go to the hospital immediately. However, if she suspects that the bleeding is the bloody show, she should call the doctor first. The doctor can determine how quickly she needs to be seen based on the amount and duration of bleeding and the presence of signs of labor.
Doctors first ask questions about the bleeding and other symptoms and about the medical history. Doctors then do a physical examination. What they find during the history and physical examination often suggests a cause of the pain and the tests that may need to be done (see Table: Some Causes and Features of Vaginal Bleeding During Late Pregnancy).
Doctors ask about the bleeding:
The woman is asked about her pregnancies: how many times she has been pregnant, how many children she has had, and whether she has had any miscarriages or abortions or any problems in previous pregnancies. The woman is asked whether the membranes have ruptured (whether her water broke), usually a sign that labor is starting or has started.
Doctors ask about conditions that increase the risk of the most common and serious causes of bleeding and about risk factors for these causes (see above), particularly a cesarean delivery in a previous pregnancy.
During the physical examination, doctors first check for signs of substantial blood loss, such as a racing heart and low blood pressure. They also check the heart rate of the fetus and, if possible, start monitoring the fetus’s heart rate constantly (with electronic fetal heart monitoring—see Monitoring the Fetus). Doctors gently press on the abdomen to determine how large the uterus is, whether it is tender, and whether its muscle tone is normal. They then do a pelvic examination. They examine the cervix using an instrument that spreads the walls of the vagina apart (speculum).
Normally when delivery is near, doctors examine the cervix with a gloved hand to determine how dilated the cervix is and how the fetus is positioned (see Labor). However, if bleeding occurs during late pregnancy, ultrasonography is done to check for placenta previa and vasa previa before this examination is done. If either disorder is present, the examination is not done because it may make the bleeding worse.
Some Causes and Features of Vaginal Bleeding During Late Pregnancy
The following tests are done:
Ultrasonography using an ultrasound device placed in the vagina (transvaginal ultrasonography) is often necessary to diagnose the cause of bleeding during late pregnancy. It can show the location of the placenta, umbilical cord, and blood vessels. Thus, it can help doctors rule out or identify placenta previa and vasa previa. However, ultrasonography cannot reliably distinguish placental abruption from rupture of the uterus. Doctors distinguish them based on results of the examination, including information about risk factors. Laparotomy is done to confirm a ruptured uterus. For this surgical procedure, doctors make an incision into the abdomen and pelvis so that they can directly view the uterus.
A complete blood cell count is done. Blood type and Rh status are determined so that a donor with a compatible blood type can be identified in case the woman needs a transfusion. If bleeding is profuse or if placental abruption is suspected, blood tests for disseminated intravascular coagulation are done. These tests include
If the woman has Rh-negative blood, a blood test (Kleihauer-Betke test) may be done to measure how many of the fetus’s red blood cells are in the woman’s bloodstream. The results can help doctors determine how much Rh0(D) immune globulin the woman should be given to prevent her from producing antibodies that may attack the fetus's red blood cells in subsequent pregnancies.
The disorder causing the bleeding is treated.
For placental abruption or placenta previa, bed rest in the hospital is usually recommended. There, the woman and fetus can be monitored, and treatment is readily available. If the bleeding stops, the woman is encouraged to walk and may be sent home. If bleeding continues or worsens or if the pregnancy is near term, the baby is delivered. Cesarean delivery is usually used if women have placenta previa and sometimes if women have placental abruption.
If vasa previa is diagnosed before labor starts, doctors schedule a cesarean delivery before labor starts, typically a few weeks before the due date. If placenta previa is diagnosed during labor, cesarean delivery is done. If the baby has lost a lot of blood, the baby may require a blood transfusion.
If the uterus has ruptured, the baby is delivered immediately. The uterus is repaired surgically.
If the woman has lost a lot of blood, she is given fluids intravenously. If this treatment is inadequate, she is given blood transfusions.
Usually, a small vaginal discharge of blood mixed with mucus (bloody show) signals the start of labor.
The severity of the bleeding does not always indicate the seriousness of the cause.
Ultrasonography is done to help doctors identify serious disorders that can cause bleeding during late pregnancy.
A woman with bleeding during late pregnancy may be hospitalized so that she and her fetus can be monitored and treated as needed.
If bleeding is profuse, the woman may need to be given fluids intravenously or a blood transfusion.