Vaginal bleeding in the third trimester can be very worrisome to a patient and clinician. When evaluating a patient with this problem, it is important to consider all the possible diagnoses in order to arrive at the appropriate conclusion and treatment. The most common causes of third-trimester vaginal bleeding are:
Cervical bleeding associated with cervical change will be discussed in the section on the evaluation of preterm labor and labor at term.
Abruptio placentae (placental abruption) is defined as the premature separation of the normally implanted placenta from the uterine wall after 20 weeks of gestation but prior to the delivery of the infant. It is diagnosed retrospectively, evident only when the inspection of the placenta reveals a clot over the placental bed with disruption of the underlying placental tissue. The placental tissue may not show overt evidence of disruption if the abruption-to-delivery interval is short. One-third of all antepartum bleeding in the third trimester is due to placental abruption, and it will occur in 1 in 75–225 deliveries. About 1 in 830 abruptions end in fetal demise.
Placental abruption may be the end of a chronic vascular pathologic process or may be due to a single inciting event. Bleeding due to vascular disruption accumulates and tracks along the decidua, separating the placenta from the remaining decidual layer. This may result in a partial abruption, referring to a self-limited hematoma that does not dissect the placental attachment further, or it may proceed to a complete abruption, leaving no decidual interface intact.
Abruption can be classified into 3 broad categories that allow for a description of the clinical and laboratory findings
Grade 1: A small amount of vaginal bleeding and abnormal uterine activity or irritability are usually noted. The fetal heart rate tracing is within normal limits. Maternal hemodynamic status is normal, and all coagulation studies and laboratory values are within normal limits.
Grade 2: A mild to moderate amount of vaginal bleeding is noted. Uterine activity may be tetanic or with frequent palpable and painful contractions. The fetal heart rate tracing may show decreased variability or late decelerations. Maternal hemodynamic status shows signs of compensation, including orthostatic hypotension and tachycardia, while maintaining overall blood pressure. Maternal fibrinogen may be decreased.
Grade 3: External uterine bleeding may range from mild (likely concealed) to severe. The uterus is typically painful and tetanic. Fetal death has occurred. Maternal hemodynamic status is unstable, showing signs of severe volume depletion with hypotension and tachycardia. Thrombocytopenia and coagulation panel value abnormalities are present. Fibrinogen concentration level is typically < 150 mg/dL.