Vaginal Bleeding in Late Pregnancy
Significant Spotting Should be Evaluated to Rule Out Serious Causes
Jul 16, 2009 Stephen Allen Christensen
Although several benign conditions can cause vaginal bleeding during the last half of pregnancy, any significant blood loss during the second and third trimesters can signal a potentially serious problem.
Unfortunately, in most cases it is not possible to determine the underlying cause of vaginal bleeding without a medical examination, and effective management of such bleeding requires prompt recognition of potentially serious conditions such as placental abruption, placenta previa, and vasa previa.
Bleeding Caused by Placental Abruption (Abruptio Placentae)
Placental abruption is the premature separation of a normally-implanted placenta from the uterine wall. Abruption can involve any degree of separation, from a few millimeters to complete detachment of the placenta.
Placental abruption is the most common cause of serious vaginal bleeding during late pregnancy, occurring in about 1 percent of all pregnancies.
Approximately one-half of abruptions occur prior to the 36th week of pregnancy, leading to additional complications associated with premature delivery. Infant death occurs in 10 to 30% of placental abruptions.
Risk factors for placental abruption include:
- Older maternal age
- Hypertension (high blood pressure)
- Tobacco, cocaine, or methamphetamine use
- Clotting abnormalities
- Abdominal trauma
- Previous placental abruption
- Uterine fibroids
- Sudden decompression of an over-distended uterus (i.e., following delivery of a first twin or rupture of membranes)
Signs and symptoms of placental abruption:
- *Vaginal bleeding (blood can be bright red, dark, or mixed with amniotic fluid)
- Sudden onset of labor, with persistent pain between contractions
- Tenderness over uterus
- Back pain
- Signs of shock if blood loss is significant (rapid heart rate, light-headedness, low blood pressure, shortness of breath, fainting, chest pain)
- Disseminated intravascular coagulation (due to release of thromboplastin into maternal circulation)
*Bleeding may be absent if the blood remains behind the placenta
Bleeding Caused by Placenta Previa
Placenta previa occurs when the placenta is implanted over or near the internal cervical os (the opening to the birth canal). Placenta previa is termed “complete” when the os is covered, “partial” when the placenta covers only part of the os, and “marginal” when the placental edge is within 2 cm of the os.
Placenta previa is commonly seen on routine ultrasound examination before 20 weeks’ gestation, but—as pregnancy progresses and the uterus expands—nearly 90% of these resolve prior to delivery.
Risk factors for placenta previa include:
- Chronic hypertension
- Multiparity (second or succeeding pregnancy)
- Multiple gestations (i.e., twins, etc.)
- Older maternal age
- Previous cesarean delivery
- Tobacco use
- Prior uterine curettage (D&C)
Signs and symptoms of placenta previa:
- Many cases are asymptomatic; these women can continue normal activities. Repeat ultrasound is performed to evaluate for persistence or resolution
- Symptomatic previa often manifests as a painless “sentinel bleed” following intercourse; this initial bleeding is usually not sufficient to induce shock or threaten the fetus
- When significant bleeding does occur, it can be spontaneous, painless, and massive, leading to maternal shock. Bleeding can be precipitated or worsened by digital vaginal examination
Bleeding Caused by Vasa Previa
Vasa previa occurs when the umbilical cord inserts in the lower section of the uterus, leading to the existence of fetal blood vessels between the fetus and the internal cervical os. Any hemorrhage arising from these vessels is fetal blood and can quickly cause fetal death, as the average blood volume in a term fetus is only 250 ml.
Vasa previa is relatively rare, occurring in 1 in 2,500 pregnancies.
Risk factors for vasa previa:
- In vitro fertilization
- Low-lying and second-trimester placenta previa
- Low-lying cord insertion
- Multiple gestation
- Placenta with multiple lobes
Signs and symptoms of vasa previa:
- If not diagnosed prior to onset of labor, usually manifests as hemorrhage at the time of amniotomy or spontaneous rupture of membranes
- Pulsating vessels may be felt in presenting membranes during cervical examination during labor
Prevention and Management of Late-Term Vaginal Bleeding
- Lifestyle changes to eliminate certain risk factors (smoking, drug use, etc.) are critical.
- Early prenatal care, including repeat ultrasound examinations, will usually identify most serious causes of late-term vaginal bleeding.
- Once placenta previa or vasa previa is diagnosed, problems can be anticipated, and cesarean delivery can be accomplished with minimal risk (infants cannot be safely delivered through a placenta previa or vasa previa).
- Bedrest and pelvic rest may be recommended for placenta previa that persists into the third trimester.
- Placental abruption often occurs without warning. Maternal evaluation and fetal monitoring are necessary to minimize life-threatening complications; emergent delivery may be indicated.
Any significant vaginal bleeding that occurs during pregnancy should prompt medical evaluation. Bleeding that is accompanied by signs of shock should be considered a medical emergency; immediate medical attention is advised so intravenous access, fluid resuscitation, transfusion, and cesarean delivery can be offered as needed.
(From Sakornbut E, et al. Late pregnancy bleeding. Am Fam Phys. 2007;75(8):1199-1206 and The Merck Manual, 18th Edition. Abnormalities of Pregnancy: Abruptio placentae; Placenta previa. 2006:2191-2; 2196-7)
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