During late pregnancy (after 20 weeks), 3 to 4% of women have vaginal bleeding. Bleeding may be a signal that there is a risk of losing the baby or of bleeding excessively (hemorrhaging). In rare cases, 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).
Women with vaginal bleeding during late pregnancy should go to the doctor to be evaluated promptly, because the bleeding may be associated with complications that threaten the safety of the woman and/or the fetus.
Causes of Vaginal Bleeding in Late Pregnancy
The most common cause of bleeding during late pregnancy is
The start of labor
In late pregnancy, some women pass the mucus plug (collection of mucus in the cervix) through the vagina. The mucus plug is usually a sticky small ball and often has streaks of blood in it. Passing the mucus plug is not the start of labor, but it is often a signal that labor will begin within the next week. 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 the following:
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 approximately 20% of bleeding during late pregnancy and is most common during the 3rd trimester. The placenta may be low-lying earlier in pregnancy, but the placenta usually moves out of the way on its own before the 3rd trimester.
Vasa previa is a rare condition in which 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, or even fatal, for the fetus.
In placental abruption, the placenta detaches from the uterus before delivery. 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 approximately 30% of cases. Placental abruption may occur at any time but is most common during the 3rd trimester.
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 other uterine surgery (such as myomectomy to remove uterine fibroids).
Bleeding may also result from disorders unrelated to pregnancy.
Risk factors
Various conditions (risk factors) increase the risk of disorders that can cause bleeding during late pregnancy.
For placenta previa, risk factors include the following:
A cesarean delivery in a previous pregnancy
One or more previous pregnancies
Placenta previa in a previous pregnancy
Age over 35
Cigarette smoking
In vitro fertilization (fertilization of the egg in a laboratory and placement of the embryo in the uterus)
For vasa previa, risk factors include the following:
A placenta located low in the uterus
A placenta that is divided into sections
For placental abruption, risk factors include
Age over 35
One or more previous pregnancies
Placental abruption in a previous pregnancy
A recent abdominal injury (as may occur in a car accident)
For rupture of the uterus, risk factors include the following:
A cesarean delivery in a previous pregnancy
Any prior surgery involving the uterus
Age over 30
Previous infections of the uterus
Artificial starting (induction) of labor
Injury, as may occur in a car crash
Birth of more than five babies
Pregnancies that are too close together
Placenta accreta (a placenta that grows too deeply into or through the uterus)
Evaluation of Vaginal Bleeding in Late Pregnancy
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.
Warning signs
Any vaginal bleeding late during pregnancy is considered a warning sign, except for the mucus plug or bloody show, which only has a small amount of blood and does not last long.
Doctors are particularly concerned about women who have fainted, feel light-headed, or have a rapid heart rate—symptoms that suggest very low blood pressure.
The following symptoms are also cause for concern:
A tense, tender uterus
No heartbeat or a slow heart rate in the fetus
Labor that stops and loss of muscle tone in the uterus
When to see a doctor
A woman with vaginal bleeding during late 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.
What the doctor does
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:
How long it lasts
How severe it is
What color the blood is
Whether the woman has or has had other symptoms (such as abdominal pain, light-headedness, or fainting)
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, particularly a cesarean delivery in a previous pregnancy.
During the physical examination, doctors first check for signs of substantial blood loss, such as a rapid heart rate 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). 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 (digital cervical examination) 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. Women who know they have placenta previa or vasa previa should feel empowered to remind clinicians of their diagnosis and refuse having a digital cervical examination. (Careful speculum examination can be done.)
Testing
The following tests are done:
Fetal heart rate monitoring
Ultrasonography
A complete blood cell count
Sometimes, blood tests to determine whether blood is clotting normally
Blood type and Rh status (positive or negative)
When bleeding occurs in pregnancy, the doctor assesses maternal vital signs, does a physical examination, and evaluates the fetus with a fetal heart rate monitor or ultrasonography.
Ultrasonography is also done to try to find the cause of the bleeding. An ultrasound device placed in the vagina (transvaginal ultrasonography) may be used to determine 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 does not always detect a placental abruption. Doctors evaluate for placental abruption and uterine rupture based on results of the physical examination, including information about risk factors.
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 the bleeding is heavy or if the doctor suspects a placental abruption, blood tests for disseminated intravascular coagulation are done.
Treatment of Vaginal Bleeding in Late Pregnancy
The disorder causing the bleeding is treated, if possible.
For placental abruption or placenta previa, if delivery is not required and the pregnant woman and fetus are healthy, admission to the hospital is usually recommended. There, the woman and fetus can be monitored, and treatment is readily available. If the bleeding stops, the woman may be sent home. If bleeding continues or worsens or if the pregnancy is near term, the baby is delivered. In women with placenta previa, cesarean delivery is required. Women who have a placental abruption may have a vaginal or cesarean delivery.
If vasa previa is diagnosed, doctors schedule a cesarean delivery before labor starts, typically at 34 to 37 weeks of pregnancy. However, if bleeding is occurring in a person with a vasa previa, it may be necessary to do a cesarean delivery as soon as possible.
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 fluid treatment is inadequate, she is given blood transfusions.
Key Points
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 there is a large amount of bleeding, the woman may need to be given fluids intravenously or a blood transfusion.
